U.S. patent application number 14/468103 was filed with the patent office on 2014-12-11 for polymer-doped vertically-aligned nematic liquid crystals.
This patent application is currently assigned to LC VISION, LLC. The applicant listed for this patent is Julia A. KORNFIELD, Zuleikha KURJI, Michael WAND. Invention is credited to Julia A. KORNFIELD, Zuleikha KURJI, Michael WAND.
Application Number | 20140362335 14/468103 |
Document ID | / |
Family ID | 45530736 |
Filed Date | 2014-12-11 |
United States Patent
Application |
20140362335 |
Kind Code |
A1 |
KORNFIELD; Julia A. ; et
al. |
December 11, 2014 |
POLYMER-DOPED VERTICALLY-ALIGNED NEMATIC LIQUID CRYSTALS
Abstract
A system having a vertically-aligned negative delta E nematic
liquid crystal host material and a small amount of liquid crystal
polymer is provided. The liquid crystal polymer improves the
switching speed of a vertically aligned nematic system without
sacrificing contrast or viewing angle.
Inventors: |
KORNFIELD; Julia A.;
(Pasadena, CA) ; WAND; Michael; (Boulder, CO)
; KURJI; Zuleikha; (Pasadena, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KORNFIELD; Julia A.
WAND; Michael
KURJI; Zuleikha |
Pasadena
Boulder
Pasadena |
CA
CO
CA |
US
US
US |
|
|
Assignee: |
LC VISION, LLC
Boulder
CO
CALIFORNIA INSTITUTE OF TECHNOLOGY
Pasadena
CA
|
Family ID: |
45530736 |
Appl. No.: |
14/468103 |
Filed: |
August 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13194297 |
Jul 29, 2011 |
8834742 |
|
|
14468103 |
|
|
|
|
61369574 |
Jul 30, 2010 |
|
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Current U.S.
Class: |
349/186 ;
252/299.62; 252/299.63; 252/299.64; 252/299.66 |
Current CPC
Class: |
C09K 19/3847 20130101;
C09K 2019/3016 20130101; C09K 2019/301 20130101; C09K 19/406
20130101; C09K 19/3842 20130101; C09K 19/3003 20130101; C09K
2019/3004 20130101; C09K 2019/3009 20130101 |
Class at
Publication: |
349/186 ;
252/299.63; 252/299.66; 252/299.64; 252/299.62 |
International
Class: |
C09K 19/38 20060101
C09K019/38 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT
[0002] This invention was made with government support under
IIP0946085 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A nematic liquid crystal composition, comprising: a negative
delta epsilon liquid crystal host; and between 0.01 and 5 wt % of a
liquid crystal polymer wherein the liquid crystal polymer has the
structure (FX1): ##STR00101## wherein PX is a polymer backbone
selected from, ##STR00102## [--(CH.sub.2--CH--S).sub.n--],
[--(NH--CH--C(.dbd.O)).sub.n--],
[--(--C(.dbd.O)--N--C(.dbd.O)).sub.n--],
[--(Si(CH.sub.3)--O).sub.n--],
[--(CH.sub.2--CH(C(O).dbd.O)).sub.n--],
[--(CH.sub.2--C(CH.sub.3)(C(O).dbd.O)).sub.n--],
[--(CH.sub.2CH).sub.n--], [--(CH(CH.sub.2CH.sub.2)).sub.n--] and
[--(CH.sub.2--CH(CH.sub.2CH.sub.2)).sub.n--] where, in each PX, n
is independently an integer between 30 to 10000; W is a
straight-chain or branched hydrocarbon group spacer having between
1 to 40 carbon atoms, wherein one or more adjacent or nonadjacent
--CH.sub.2-- groups in the hydrocarbon group can be independently
replaced with --S--, --S(.dbd.O)--, --O--, --C(.dbd.O)--,
--O--C(.dbd.O)--, --(Si--R.sup.40R.sup.41)--,
--[OSiR.sup.40R.sup.41].sub.d--, --[Si(R.sup.40R.sup.41)O].sub.d--,
--[Si(R.sup.40R.sup.41)--(OSiR.sup.40R.sup.41).sub.d]--,
--OSiR.sup.40R.sup.41O--, --CF.sub.2--, and --GeR.sup.40R.sup.41--,
where R.sup.40 and R.sup.41 are each independently a hydrogen or a
C1-C5 straight chain or branched alkyl group wherein any hydrogen
may be replaced with fluorine, and wherein d is independently an
integer from 1 to 6; M is a mesogen.
2. The nematic liquid crystal composition of claim 1 wherein M is:
##STR00103## wherein b and e are independently 0 or 1; bb is an
integer from 0 to 10; aa is an integer from 0 to 10; and each A,
R.sup.1 and R.sup.2 is independently a cycloalkane ring having from
3 to 8 carbons, independently a cycloalkene ring having from 3 to 8
carbons, an aromatic ring, or a fused two or three ring structure;
where there may be from 1 to 6 cycloalkane rings and from 0 to 5
aromatic rings in M; each L is independently selected from a direct
bond, --O--, --O--C(.dbd.O)--, --C(.dbd.O)--O--, --C.dbd.C--,
--C.ident.C--, --(CH.sub.2).sub.u--; where u is an integer from 1
to 10; wherein one or more ring carbon atoms in one or more of A,
R.sup.1 and R.sup.2 may be replaced with --N--, --S--, and --O--;
one or more hydrogens on any of A, R.sup.1 and R.sup.2 can be
independently replaced with fluorine, chlorine, bromine,
--CF.sub.3, --OCF.sub.3, --OCF.sub.2H and --OCFH.sub.2; and wherein
each T is a terminating group independently selected from hydrogen,
--CN, or a one- to fifteen-carbon alkyl, alkoxy or alkenyl chain
wherein one or more hydrogen atoms may be independently replaced
with fluorine and one or more --CH.sub.2-- groups may be
independently replaced with --O-- or --O(C.dbd.O)--.
3. The nematic liquid crystal composition of claim 1 wherein the
negative delta epsilon liquid crystal host is selected from nematic
liquid crystal compositions comprising compounds having
4'-alkylbicyclohexyl-2,3-difluoro-4-alkyloxyphenyl and
4'-cyclohexyl-2,3-difluoro-4-alkyloxyphenylbenzene groups.
4. The nematic liquid crystal composition of claim 1 wherein the
negative delta epsilon liquid crystal host has a delta epsilon of
less than 0.
5. The nematic liquid crystal composition of claim 1 wherein the
liquid crystal polymer has a delta epsilon value of between -5 and
-10.
6. The nematic liquid crystal composition of claim 1 wherein the
liquid crystal polymer has a delta epsilon value of greater than
0.
7. The nematic liquid crystal composition of claim 1 wherein the
liquid crystal polymer has a delta epsilon value of less than
0.
8. The nematic liquid crystal composition of claim 1, wherein W is
--(CR.sup.15R.sup.16).sub.y--, where y is an integer from 1 to 40;
wherein R.sup.15 and R.sup.16 are each independently hydrogen or
halogen; wherein any adjacent or nonadjacent
--(CR.sup.15R.sup.16)-- group can be independently replaced with
--S--, --S(.dbd.O)--, --O--, --C(.dbd.O)--, --O--C(.dbd.O)--,
--(Si--R.sup.40R.sup.41)--, --[OSiR.sup.40R.sup.41].sub.d--, --[Si
(R.sup.40R.sup.41)O].sub.d--, --[Si
(R.sup.40R.sup.41)--[OSiR.sup.40R.sup.41].sub.d]--,
--OSiR.sup.40R.sup.41O--, --CF.sub.2--, and --GeR.sup.40R.sup.41--,
where R.sup.40 and R.sup.41 are each independently a hydrogen or a
C1-C5 straight chain or branched alkyl group wherein any hydrogen
can be replaced with fluorine, and wherein d is independently an
integer from 1 to 6.
9. The nematic liquid crystal composition of claim 1, wherein W is
--(CH.sub.2).sub.r--[Si(CH.sub.3).sub.2].sub.m--(CH.sub.2).sub.nn--[Si(CH-
.sub.3).sub.2].sub.m--(CH.sub.2).sub.r--O--[(C.dbd.O)].sub.z--,
wherein each r and nn is independently an integer from 0 to 6, each
m is independently an integer from 0 to 6; z is 0 or 1.
10. The nematic liquid crystal composition of claim 1 wherein M is
selected from: ##STR00104## ##STR00105##
11. The nematic liquid crystal composition of claim 1, wherein in
the liquid crystal polymer, M is a fused three ring structure
having the formula: ##STR00106## where each R is independently
C1-C6 alkyl.
12. The nematic liquid crystal composition of claim 1, wherein in
the liquid crystal polymer, M has the structure ##STR00107## where
R is a C1-C6 alkyl or alkoxy or is CN.
13. The nematic liquid crystal composition of claim 2, wherein each
A, R.sup.1 and R.sup.2 is independently selected from: ##STR00108##
where each X.sup.5, X.sup.6, X.sup.7, X.sup.8, X.sup.9, X.sup.10
and X.sup.11 can be independently replaced with --N--, --S-- or
--O--; each X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.12, X.sup.13,
X.sup.14, X.sup.15, X.sup.16, X.sup.17, and X.sup.18 is
independently hydrogen, --F, or --CF.sub.3.
14. The nematic liquid crystal composition of claim 1, wherein M is
selected from: ##STR00109## where R.sup.25 is C1-C6 alkyl or C1-C6
alkoxy.
15. The nematic liquid crystal composition of claim 1, wherein the
liquid crystal polymer has the structure (FX9), (FX10) or (FX9A):
##STR00110## ##STR00111## where n is an integer from 500 to 1,000
and a is an integer from 5 to 9.
16. A nematic liquid crystal composition, comprising: a negative
delta epsilon nematic liquid crystal host; and between 0.01 and 5
wt % of a liquid crystal polymer, wherein the liquid crystal
polymer has the structure (FX11): ##STR00112## wherein PX is a
polymer backbone; W is a thiol or siloxy-containing spacer; M is a
mesogen, EG is a polystyrene end group, and each i is independently
0 or 1.
17. The liquid crystal composition of claim 16, wherein one i is 1
and one i is 0.
18. The liquid crystal composition of claim 16, wherein the liquid
crystal polymer has the structure (FX12A): ##STR00113## where i is
1; EG is ##STR00114## where d is independently an integer from 100
to 1000 and each R.sup.10, R.sup.11 and R.sup.12 is independently
hydrogen, halogen or --CN; PX is ##STR00115##
[--(CH.sub.2--CH--S).sub.n--], [--(NH--CH--C(.dbd.O)).sub.n--],
[--(--C(.dbd.O)--N--C(.dbd.O)).sub.n--],
[--(Si(CH.sub.3)--O).sub.n--],
[--(CH.sub.2--CH(C(O).dbd.O).sub.n--],
[--(CH.sub.2--C(CH.sub.3)(C(O).dbd.O).sub.n--],
[--(CH.sub.2CH).sub.n--], [--(CH(CH.sub.2CH.sub.2))--.sub.n] or
[--(CH.sub.2--CH(CH.sub.2CH.sub.2)).sub.n--] where in each PX n is
independently an integer between 50 to 10000; W is a spacer
selected from --S--, --S(.dbd.O)--, --O--, --C(.dbd.O)--,
##STR00116## where q is an integer from 0 to 10; t is an integer
from 1 to 10; R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each
independently selected from optionally substituted C.sub.1-C.sub.6
alkyl, where the optional substituents are one or more halogens;
each L is independently selected from: --O--C(.dbd.O)--,
--C(.dbd.O)--O--, --C.dbd.C--, --C.ident.C--, --(CH.sub.2).sub.u--;
and a single bond; where u is an integer from 1 to 10; R.sup.1 and
R.sup.2 are each independently selected from: ##STR00117## where
X.sup.1, X.sup.2, X.sup.3 and X.sup.4 are independently hydrogen,
halogen, methoxy, C1-C.sub.3 alkyl or --CN; where (a) each Z and
each Y is CH, or (b) each Z is N and each Y is CH, or (c) each Y is
N and each Z is CH; R.sup.7 and R.sup.8 are each independently
hydrogen, halogen, and --(O).sub.v--(CH.sub.2).sub.p--CH.sub.3
where p is an integer from 0 to 20 and v is 0 or 1 and where
R.sup.30 and R.sup.31 are each independently hydrogen or
halogen.
19. An optical device comprising: two opposing electrode surfaces;
the nematic liquid crystal composition of claim 1 disposed
therebetween.
20. A method of preparing a nematic liquid crystal composition,
comprising: contacting a nematic liquid crystal host; and between
0.01 and 5 wt % of a liquid crystal polymer which is soluble in the
nematic liquid crystal host.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/194,297, filed Jul. 29, 2011, which claims
the benefit of and priority to U.S. Provisional Application Ser.
No. 61/369,574, filed Jul. 30, 2010, each of which is incorporated
by reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to liquid crystals,
and more particularly to nematic liquid crystals.
[0004] The public's growing demand for the superior image quality
provided by high definition televisions (HDTVs) has resulted in
ongoing growth of HDTV sales. To compete in toddy's market, a
display needs to meet three main criteria: high contrast, good
viewing angle and fast response times. Vertically Aligned Nematic
(VAN) Liquid Crystal Displays (LCDs) have inherently high contrast
and, with some simple modifications, good viewing angle. Due to
their excellent high contrast relative to twisted-nematic (TN) LC
displays (familiar in laptop computers, for example), VAN-LCDs
dominate the market in large-size LCD panels for high definition
televisions (HDTVs). However, the very high contrast of VAN-LCDs
comes at the expense of the response time of the display: a pixel
in a current VAN display requires approximately 100 ms to switch
(rise-time+fall-time), compared to less than 20 ms for a TN
display.
[0005] Some attempts have been made to improve the switching speed
of a VA display by adding a small amount of reactive monomer within
the liquid crystal and polymerizing during processing. Although
polymer-stabilized vertical-alignment (PS-VA) technology improves
the switching speed in HD LCD, there are drawbacks to current PS-VA
technology. Current PS-VA technology introduces a difficult
irradiation step during processing to induce polymerization of the
monomer, which requires precise control of the uniformity and the
duration of UV irradiation. Also, the radical and ionic species
created during UV radiation have long-term deleterious effects on
the LCD (such as increasing the power consumption and reducing the
display lifetime).
[0006] There is a need for vertically aligned nematic liquid
crystal systems having faster response times without sacrificing
contrast.
BRIEF SUMMARY OF THE INVENTION
[0007] Provided is a technology that significantly improves both
the processing and device characteristics of vertically aligned
nematic liquid crystal systems. The system described here generally
uses polymers synthesized and purified outside of the display that
are added at low concentration to the nematic liquid crystal that
makes up the active medium of the LCD. The material comprising a
small concentration of polymer dissolved in a liquid crystal is
referred to as a polymer-doped LC (PD-LC). It was found that the
PD-LC system described here can increase contrast (eliminating or
reducing the problem of light leakage that plagues PS-VA
technology, for example) and improve switching speed without
introducing ionic and radical impurities produced during UV
irradiation. By using polymer dopants that dissolve uniformly in
the active medium of the display, in an aspect the system described
here maintains the optical uniformity of the LC and avoids the
polymerization-induced phase-separation that occurs during
photopolymerization of monomers in LCs. Very low concentrations of
polymer dopant are sufficient to produce improvements in the
physical properties of VAN systems.
[0008] In an aspect, polymer-doped LCs which maintain the excellent
dark state and high contrast that are the hallmarks of vertically
aligned nematic liquid crystal displays and that improve one or
more liquid crystal display properties including increasing the
switching speed, enhancing the brightness, and improving the
viewing angle of vertically-aligned nematic liquid crystal displays
(VAN-LCDs) are provided. In an aspect, the polymer dopants provided
confer these benefits without detrimental effects on the cell's
threshold voltage or saturation voltage. In an aspect, the
compositions provided are fundamentally different than existing
monomer-doped in situ polymerized LCs used in PS-VA technology
because the compositions provided eliminate exposure of the liquid
crystal to UV light and its concomitant radical contamination.
Devices free of radical contamination have increased display
lifetimes in addition to their advantageous switching speeds and
optical properties.
[0009] More specifically, provided is a system comprising a
conventional vertically aligned nematic liquid crystal ("VAN") host
material and a small amount of a liquid crystal polymer. "Liquid
crystal polymer" is defined as a polymer that comprises at least
one portion that includes a mesogen. In an embodiment, a "liquid
crystal polymer" is a polymer having one or more mesogens attached
thereto. The liquid crystal polymer does not need to be liquid
crystalline in its pure state. As used herein, "mesogenic side
group" or "mesogen" or M and other variations of the phrases is a
group which can be useful to confer characteristics to the
composition to allow the polymer to be soluble in the host and
provide orientational coupling between the polymer and host. In an
embodiment, a mesogen is a core from a liquid crystal composition.
"Liquid crystal polymer", "dopant", "side group liquid crystal
polymer" "polymer doped VAN" "polymer additive" and other
variations of the phrases are used interchangeably herein in the
contexts as provided.
[0010] The liquid crystal polymer is present in the VAN host in
small amounts (between 0.01 and 5 wt % in embodiments). The nematic
liquid crystal host and liquid crystal polymer together are a
"nematic liquid crystal composition" as used herein. In an
embodiment the nematic liquid crystal host has a negative delta
epsilon as defined elsewhere herein.
[0011] Although applicant does not wish to be bound by theory, it
is believed that the liquid crystal polymer is soluble in the VAN
host and undergoes the change in orientation order along with the
VAN host upon processing. The liquid crystal polymer can contain
any polymer, spacer and mesogenic unit or other groups which
produce the desired effect upon introduction into the VAN host.
Some specific examples of the polymer, spacer and liquid crystal
useful in the liquid crystal polymer are shown and described
herein. In an aspect of the invention, the liquid crystal polymer
is synthesized and then added to the VAN host.
[0012] In an aspect of the invention, the switching speed of a
nematic liquid crystal composition described herein is as fast
(within 5%) or faster than the switching speed of the VAN host
without the liquid crystal polymer. In an embodiment, the optical
rise time of a nematic liquid crystal composition described herein
is approximately equal to (within 5%) or faster than the optical
rise time of the VAN host without the liquid crystal polymer. In an
embodiment, the optical fall time of a nematic liquid crystal
composition described herein is approximately equal to (within 10%)
or faster than the optical fall time of the VAN host without the
liquid crystal polymer. In an aspect of the invention, the addition
of the liquid crystal polymer to the VAN host improves the contrast
of the mixture in a cell or device. In an aspect of the invention,
response speed of devices containing the nematic liquid crystal
compositions described herein is improved as compared to the
response speed of devices which do not contain the liquid crystal
polymer, as described herein. In an aspect of the invention, the
nematic liquid crystal compositions described herein have one or
more of the effects described herein. In an aspect of the
invention, either or both of the rise time and fall time of devices
containing the nematic liquid crystal compositions described herein
is improved from 0% (i.e., no decrease in rise or fall time or
both) up to more than one hundred percent, as compared to the rise
and fall time of devices which do not contain the liquid crystal
polymer, as described herein. In an embodiment, the rise time of
devices containing the nematic liquid crystal compositions
described herein is improved from 0% (i.e., no decrease in rise
time) to an improvement of about 2.times. faster, as compared to
the rise time of devices which do not contain the liquid crystal
polymer, as described herein. In an embodiment, the fall time of
devices containing the nematic liquid crystal compositions
described herein is improved from 1% to about 50%, as compared to
the fall time of devices which do not contain the liquid crystal
polymer, as described herein.
[0013] The invention includes liquid crystal cells and devices
comprising the nematic liquid crystal compositions of the invention
including small and large area displays and devices such as camera
viewfinders and home theaters. The preparation and uses of these
cells and devices are well known to one of ordinary skill in the
art.
[0014] In an embodiment, provided is a nematic liquid crystal
composition, comprising: a negative delta epsilon liquid crystal
host; and between 0.01 and 5 wt % of a liquid crystal polymer
wherein the liquid crystal polymer has the structure (FX1):
##STR00001##
wherein PX is a polymer backbone selected from
##STR00002##
[--(CH.sub.2--CH--S).sub.n--], [--(NH--CH--C(.dbd.O)).sub.n--],
[--(--C(.dbd.O)--N--C(.dbd.O)).sub.n--],
[--(Si(CH.sub.3)--O).sub.n--],
[--(CH.sub.2--CH(C(O).dbd.O)).sub.n--],
[--(CH.sub.2--C(CH.sub.3)(C(O).dbd.O)).sub.n--],
[--(CH.sub.2CH).sub.n--], [--(CH(CH.sub.2CH.sub.2)).sub.n--] and
[--(CH.sub.2--CH(CH.sub.2CH.sub.2)).sub.n--] where, in each PX, n
is independently an integer between 30 to 10000; W is a
straight-chain or branched hydrocarbon group spacer having between
1 to 40 carbon atoms, wherein one or more adjacent or nonadjacent
--CH.sub.2-- groups can be independently replaced with --S--,
--S(.dbd.O)--, --O--, --C(.dbd.O)--, --O--C(.dbd.O)--,
--(Si--R.sup.40R.sup.41)--, [--OSiR.sup.40R.sup.41].sub.d--,
--[Si(R.sup.40R.sup.41)O].sub.d--,
--[Si(R.sup.40R.sup.41)--(OSiR.sup.40R.sup.41).sub.d]--,
--OSiR.sup.40R.sup.41O--, --CF.sub.2--, and --GeR.sup.40R.sup.41--,
where R.sup.40 and R.sup.41 are each independently a hydrogen or a
C1-C5 straight chain or branched alkyl group wherein any hydrogen
may be replaced with F, Cl, Br, --CH.sub.3, --OCF.sub.3,
--OCF.sub.2H, and OCFH.sub.2; and wherein d is independently an
integer from 1 to 6; and M is a mesogen.
[0015] In an embodiment, in the liquid crystal polymer, M is:
##STR00003##
wherein b and e are independently 0 or 1; bb is an integer from 0
to 10; aa is an integer from 0 to 10; and each A, R.sup.1 and
R.sup.2 is independently either a cycloalkane ring having from 3 to
8 carbons, an aromatic ring, or a fused two or three ring
structure; where there may be from 1 to 6 cycloalkane rings and
from 0 to 5 aromatic rings in M; each L is independently selected
from a direct bond, --O--, --O--C(.dbd.O)--, --C(.dbd.O)--O--,
--C.dbd.C--, --C.ident.C--, --(CH.sub.2).sub.u--; where u is an
integer from 1 to 10; wherein one or more ring carbon atoms in one
or more of A, R.sup.1 and R.sup.2 may be replaced with --N--,
--S--, and --O--; one or more hydrogens on any of A, R.sup.1 and
R.sup.2 can be independently replaced with fluorine, chlorine,
bromine, --CF.sub.3, --OCF.sub.3, --OCF.sub.2H and --OCFH.sub.2;
and wherein one or more hydrogen atoms in M may be independently
replaced with replaced with fluorine, chlorine, bromine,
--CF.sub.3, --OCF.sub.3, --OCF.sub.2H and --OCFH.sub.2; and wherein
each T is a terminating group independently selected from hydrogen,
--CN, or a one- to fifteen-carbon alkyl, alkoxy or alkenyl chain
wherein one or more hydrogen atoms may be replaced with fluorine
and one or more --CH.sub.2-- groups may be replaced with --O-- or
--O(C.dbd.O)--. In an embodiment in any of the structures shown
herein, including FX1, n in the polymer backbone is an integer from
30 to 49. In an embodiment each A, R.sup.1 and R.sup.2 is
independently selected from:
##STR00004##
where each X.sup.5, X.sup.6, X.sup.7, X.sup.8, X.sup.9, X.sup.10
and X.sup.11 can be independently replaced with --N--, --S-- or
--O--; each X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.12, X.sup.13,
X.sup.14, X.sup.15, X.sup.16, X.sup.17, and X.sup.18 is
independently hydrogen, fluorine, chlorine, bromine, --OCF.sub.3,
--OCF.sub.2H and --OCFH.sub.2, or --CF.sub.3. In an embodiment, in
the structures shown herein, PX is independently one or more of the
polymer backbone structures shown for FX1. In the structures shown
herein, one of ordinary skill in the art will recognize that two
adjacent --O-- groups and two adjacent --S-- groups would form
unstable peroxide linkages and disulfide linkages and would not be
preferred. In an embodiment of the invention, there are not two
adjacent oxygen or two adjacent sulfur atoms present in the
compositions described here.
[0016] In embodiments, a mesogen may be present at any location in
the overall polymer. In an embodiment, a mesogen is present in the
polymer backbone. This embodiment is also called a main chain
liquid crystal polymer. In embodiment, a mesogen is present as a
side chain on the polymer backbone. This embodiment is also called
a side group liquid crystal polymer. In any embodiment there may or
may not be a spacer present between the polymer backbone and the
mesogen. In an embodiment, a mesogen may be present both in the
polymer backbone and as a side chain on the polymer backbone. In an
embodiment, the liquid crystal polymer is a copolymer having one or
more repeating groups which may be different. In an embodiment, the
liquid crystal polymer is a mixed main chain/side group polymer,
where there is a first mesogen in a first composition polymer
backbone and a second mesogen which can be the same or different as
the first mesogen attached as a side group on a second composition
polymer backbone which may be the same or different than the first
composition polymer backbone. The mesogen and polymer can be
attached at a terminal position of the mesogen group (and the
resulting structure is called an end-on liquid crystal polymer), or
the mesogen can be attached to the polymer at an internal position
of the mesogen (and the resulting structure is called a side-on
liquid crystal polymer). All combinations of locations of one or
more mesogens relative to the polymer backbone, and the use of
suitable spacers to attach the mesogen and spacer are included to
the extent as if they were specifically listed. In an aspect, in
the liquid crystal polymers, one or more of the variables PX, W and
M may be arranged in any configuration to form the various
embodiments including main chain liquid crystal polymer, side group
liquid crystal polymer, mixed main chain/side group polymer, end-on
liquid crystal polymer, side-on liquid crystal polymer and other
possible configurations.
[0017] The liquid crystal host may be chosen for the particular
purpose and physical characteristics desired, as known in the art.
Any suitable liquid crystal host, including any negative delta
epsilon liquid crystal host may be used. In an embodiment of the
nematic liquid crystal composition, the negative delta epsilon
liquid crystal host is selected from commercially available hosts
including: MLC6608; MLC6886, and mixtures thereof. The primary
chemical structures that are used in state-of-the-art VAN LCs are
bicyclohexyl difluoro and cyclohexyl biphenyl difluoro, therefore,
the polymers tested in MLC6886 are designed to be soluble in the LC
hosts that are currently used in VAN displays. VAN host mixtures
are enhanced by viscosity lowering agents and components that
enhance the negative delta epsilon, which will not adversely affect
the present polymer dopants. In an embodiment, the negative delta
epsilon liquid crystal host is selected from nematic liquid crystal
compositions having bicyclohexyl difluoro alkoxyphenyl and
cyclobiphenyldifluoro groups. In an embodiment, the negative delta
epsilon liquid crystal host is selected from nematic liquid crystal
compositions comprising compounds having
4'-alkylbicyclohexyl-2,3-difluoro-4-alkyloxyphenyl and
4'-cyclohexyl-2,3-difluoro-4-alkyloxyphenylbenzene groups.
[0018] In an embodiment of the nematic liquid crystal composition
the liquid crystal host has a delta epsilon of less than 0 (also
referred to as "negative delta epsilon"). In an embodiment of the
nematic liquid crystal composition the liquid crystal polymer has a
delta epsilon value of between about -0.5 and -10. In an embodiment
of the nematic liquid crystal composition the liquid crystal
polymer has a delta epsilon value of greater than 0. In an
embodiment of the nematic liquid crystal composition the liquid
crystal polymer has a delta epsilon value of less than 0.
[0019] In an embodiment of the liquid crystal polymer W is
--(CR.sup.15R.sup.16).sub.y--, where y is an integer from 1 to 40;
wherein R.sup.15 and R.sup.16 are each independently hydrogen or
halogen; wherein any adjacent or nonadjacent
--(CR.sup.15R.sup.16)-- group can be independently replaced with
--S--, --S(.dbd.O)--, --O--, --C(.dbd.O)--, --O--C(.dbd.O)--,
--(Si--R.sup.40R.sup.41)--, --[OSiR.sup.40R.sup.41].sub.d--, --[Si
(R.sup.40R.sup.41)O].sub.d--, --[Si
(R.sup.40R.sup.41)--[OSiR.sup.40R.sup.41].sub.d]--,
--OSiR.sup.40R.sup.41O--, --CF.sub.2--, and --GeR.sup.40R.sup.41,
where R.sup.40 and R.sup.41 are each independently a hydrogen or a
C1-C5 straight chain or branched alkyl group wherein any hydrogen
can be replaced with fluorine, and wherein d is independently an
integer from 1 to 6.
[0020] In an embodiment of the liquid crystal polymer W is
--(CH.sub.2).sub.r--[Si(CH.sub.3).sub.2].sub.m--(CH.sub.2).sub.nn--[Si(CH-
.sub.3).sub.2].sub.m--(CH.sub.2).sub.r--O--[(C.dbd.O)].sub.z--,
wherein each r and nn is independently an integer from 0 to 6, each
m is independently an integer from 0 to 6; and z is 0 or 1.
[0021] In an embodiment of the liquid crystal polymer W is selected
from the following. The following structures are not intended to be
an exhaustive list of possible structures, but merely to provide
examples.
##STR00005##
where the lines at the top of the structures shown indicate
attachment to the rest of the liquid crystal polymer structure.
[0022] In the liquid crystal polymer, M can be any suitable
structure that provides the desired function. In an embodiment of
the liquid crystal polymer, M is a fused three ring structure
having the formula:
##STR00006##
[0023] where each R is independently C1-C6 alkyl.
[0024] In an embodiment of the liquid crystal polymer, M has the
structure
##STR00007##
[0025] where R is a C1-C6 alkyl or alkoxy.
[0026] In an embodiment of the liquid crystal polymer, M has the
structure
##STR00008##
where R is a C1-C6 alkyl or alkoxy or is CN.
[0027] In separate embodiments of the liquid crystal polymer of the
invention, M is selected from:
##STR00009##
[0028] In an embodiment of the liquid crystal polymer M is selected
from:
##STR00010##
[0029] where R.sup.25 is C1-C6 alkyl or C1-C6 alkoxy.
[0030] In an embodiment of the liquid crystal polymer mesogen M is
selected from the following structures. The following structures
are not intended to be an exhaustive list of possible structures,
but merely to provide examples. Other examples are shown elsewhere
herein.
##STR00011##
where the lines at the top of the structures shown indicate
attachment to the rest of the liquid crystal polymer structure.
[0031] In embodiments, the liquid crystal polymer has one of the
structures below where n is an integer from above 20 to 10,000. In
embodiments, the liquid crystal polymer has one of the structures
below where n is an integer from 30 to 10,000. In an embodiment,
the polymer backbone has between 30 and 100 repeating units. In an
embodiment, the polymer backbone has between 30 and 49 repeating
units. In an embodiment, the polymer backbone has between 50 and
100 repeating units. In an embodiment, the polymer backbone has
between 30 and 1,000 repeating units. In an embodiment, the polymer
backbone has between 50 and 10,000 repeating units. The structures
below are intended only as examples of the liquid crystal polymer
that can be used in the methods, compositions and devices herein
and are not limiting. Other examples of liquid crystal polymers are
shown elsewhere herein.
##STR00012## ##STR00013## ##STR00014## ##STR00015##
##STR00016##
[0032] In an embodiment of the liquid crystal polymer PX is a
polymer backbone having the formula:
##STR00017##
where n is an integer from 30 to 10,000. In an embodiment of the
liquid crystal polymer PX is a polymer backbone having the
formula:
##STR00018##
where n is an integer from 50 to 10,000. In an embodiment of the
liquid crystal polymer PX is a polymer backbone having the
formula:
##STR00019##
where n is an integer from 30 to 49. In an embodiment of the liquid
crystal polymer PX is a polymer backbone having the formula:
##STR00020##
where n is an integer from 30 to 50. All intermediate ranges and
individual values of all variables and ranges are intended to be
included to the fullest extent, including specific inclusion and
exclusion in a claim.
[0033] In an embodiment, in the liquid crystal polymer, PX is a
polymer backbone having the formula: [--(CH.sub.2--CH--S).sub.n--],
where n is an integer from 50 to 10,000. In an embodiment, in the
liquid crystal polymer, PX is a polymer backbone having the
formula: [--(NH--CH--C(.dbd.O).sub.n--], where n is an integer from
50 to 10,000. In an embodiment, in the liquid crystal polymer, PX
is a polymer backbone having the formula:
[--(--C(.dbd.O)--N--C(.dbd.O)).sub.n--]-- where n is an integer
from 50 to 10,000. In an embodiment, in the liquid crystal polymer,
PX is a polymer backbone having the formula:
[--(Si(CH.sub.3)--O).sub.n--], where n is an integer from 50 to
10,000. In an embodiment, in the liquid crystal polymer, PX is a
polymer backbone having the formula:
[--(CH.sub.2--CH(C(O).dbd.O).sub.n--], where n is an integer from
50 to 10,000. In an embodiment, in the liquid crystal polymer, PX
is a polymer backbone having the formula:
[--(CH.sub.2--C(CH.sub.3)(C(O).dbd.O).sub.n--] where n is an
integer from 50 to 10,000. In an embodiment, in the liquid crystal
polymer, PX is a polymer backbone having the formula:
[--(CH.sub.2--CH(CH.sub.2CH.sub.2)).sub.n--] where n is an integer
from 50 to 10,000. In an embodiment, in the liquid crystal polymer,
PX is a polymer backbone having the formula:
[--(CH.sub.2CH).sub.n--], where n is an integer from 50 to 10,000.
In an embodiment, in the liquid crystal polymer, PX is a polymer
backbone having the formula: [--(CH(CH.sub.2CH.sub.2))--.sub.n],
where n is an integer from 50 to 10,000.
[0034] In an embodiment, in any of the possibilities for PX, n is
an integer from 100 to 5,000. In an embodiment, in any of the
possibilities for PX, n is an integer from 500 to 1,000. In an
embodiment, in any of the possibilities for PX, n is an integer
from 30 to 49.
[0035] In an embodiment, one or more polystyrene end groups are
chemically bound to the liquid crystal polymer. In an embodiment,
no polystyrene end groups are chemically bound to the liquid
crystal polymer.
[0036] In an embodiment, provided is a nematic liquid crystal
composition, comprising: a nematic liquid crystal host; and between
0.01 and 5 wt % of a liquid crystal polymer, wherein the liquid
crystal polymer has the structure (FX11):
##STR00021##
wherein PX is a polymer backbone; W is a spacer; M is a mesogen, EG
is a polystyrene end group, and each i is independently 0 or 1. In
FX11, PX, W and M take the definitions as they appear elsewhere
herein. In this embodiment, one or more polystyrene end group
polymers are included in the liquid crystal polymer. In separate
embodiments of formula (FX11), each i is 0. In separate embodiments
of formula (FX11), one i is 1 and one i is 0. In separate
embodiments of formula (FX11), each i is 1.
[0037] In an embodiment, provided is a nematic liquid crystal
composition, comprising: a nematic liquid crystal host; and between
0.01 and 5 wt % of a liquid crystal polymer, wherein the liquid
crystal polymer has the structure (FX11A):
##STR00022##
where the variables are defined as above.
[0038] Also provided is a Also provided is a nematic liquid crystal
composition, wherein the liquid crystal polymer has the structure
(FX12):
##STR00023##
each i is 0 or 1; each EG is
##STR00024##
where d is independently an integer from 100 to 1000 and each
R.sup.10, R.sup.11 and R.sup.12 is independently hydrogen, halogen
or --CN; PX is
##STR00025##
[--(CH.sub.2--CH--S).sub.n--], [--(NH--CH--C(.dbd.O)).sub.n--],
[--(--C(.dbd.O)--N--C(.dbd.O)).sub.n--],
[--(Si(CH.sub.3)--O).sub.n--],
[--(CH.sub.2--CH(C(O).dbd.O).sub.n--],
[--(CH.sub.2--C(CH.sub.3)(C(O).dbd.O).sub.n--],
[--(CH.sub.2CH).sub.n--], [--(CH(CH.sub.2CH.sub.2))--.sub.n] or
[--(CH.sub.2--CH(CH.sub.2CH.sub.2)).sub.n--] where, in each PX, n
is independently an integer between 50 to 10000; W is
--(O).sub.b--(CR.sup.13R.sup.14).sub.x--(O).sub.b--FX--(O).sub.b--(CR.sup-
.15R.sup.16).sub.y--(O).sub.b--, where x and y are each
independently integers from 0 to 20; FX is a spacer selected from
--S--, --S(.dbd.O)--, --O--, --C(.dbd.O)--,
##STR00026##
where q is an integer from 0 to 10; t is an integer from 1 to 10;
each b is independently 0 or 1; and R.sup.3, R.sup.4, R.sup.5 and
R.sup.6 are each independently selected from optionally substituted
C.sub.1-C.sub.6 alkyl, where the optional substituents are one or
more halogens; R.sup.13, R.sup.14, R.sup.15 and R.sup.16 are each
independently hydrogen or halogen; each L is independently selected
from: --O--C(.dbd.O)--, --C(.dbd.O)--O--, --C.dbd.C--,
--C.ident.C--, --(CH.sub.2).sub.u--; and a single bond; where u is
an integer from 1 to 10; R.sup.1 and R.sup.2 are each independently
selected from:
##STR00027##
where X.sup.1, X.sup.2, X.sup.3 and X.sup.4 are independently
hydrogen, halogen, methoxy, C.sub.1-C.sub.3 alkyl or --CN; where
(a) each Z and each Y is CH, or (b) each Z is N and each Y is CH,
or (c) each Y is N and each Z is CH; R.sup.7 and R.sup.8 are each
independently hydrogen, halogen, and
--(O).sub.v--(CH.sub.2).sub.p--CH.sub.3 where p is an integer from
0 to 20 and v is 0 or 1.
[0039] Also provided in an embodiment is a nematic liquid crystal
composition described herein, wherein the liquid crystal polymer
has the structure (FX12A):
##STR00028##
where i is 1 and the variables are as defined for Formula FX12 and
where R.sup.30 and R.sup.31 are each independently hydrogen or
halogen.
[0040] In the liquid crystal polymer, the polymer backbone PX can
be any suitable polymer unit as described herein. As an embodiment
of each formula described herein, provided is an aspect wherein in
the liquid crystal polymer of the nematic liquid crystal
composition, PX is a polymer backbone having the structure:
##STR00029##
where n is an integer from 50 to 10,000.
[0041] Also provided is a nematic liquid crystal composition as
described herein wherein the liquid crystal polymer has the
structure (FX13):
##STR00030##
where each d is independently an integer from 100 to 1000; and n is
an integer from 50 to 10,000 and the other variables are as defined
for formula (FX1).
[0042] Also provided in an embodiment is a nematic liquid crystal
composition as described herein wherein the liquid crystal polymer
has the structure (FX14):
##STR00031##
where d is an integer from 100 to 1000; and n is an integer from 50
to 10,000 and the other variables are as defined for formula
(FX1).
[0043] In an aspect of the invention, provided is a liquid crystal
polymer having the structure (FX14A):
##STR00032##
where d is an integer from 100 to 1000; and n is an integer from 50
to 10,000, and the other variables are as defined for formula
(FX1).
[0044] In an aspect of the invention the liquid crystal polymer
described herein is soluble in the nematic liquid crystal host at a
temperature at which the nematic liquid crystal host is nematic. In
an aspect of the invention, compounds having all combinations of
the structures and all other components herein are intended to be
described to the fullest extent, including to provide the ability
to include or delete particular structures or components from the
claims, for example. If any variable is not defined, it is
understood that variable can take any definition that is
synthetically possible and functions in the manner described
herein.
[0045] In an embodiment the liquid crystal polymer has the
structure
##STR00033##
[0046] In an embodiment the liquid crystal polymer has the
structure
##STR00034##
[0047] In an embodiment the liquid crystal polymer has the
structure (Polymer 6):
##STR00035##
[0048] In an embodiment the liquid crystal polymer has the
structure (Polymer 7):
##STR00036##
[0049] In an embodiment of the nematic liquid crystal composition
the liquid crystal polymer has the structure (FX9), (FX10) or
(FX9A):
##STR00037## ##STR00038##
where n is an integer from 500 to 1,000 and a is an integer from 5
to 9.
[0050] In an embodiment of the nematic liquid crystal composition
the liquid crystal polymer is soluble in the nematic liquid crystal
host at a temperature at which the nematic liquid crystal host is
nematic.
[0051] Also provided is an optical device comprising two opposing
electrode surfaces which have a nematic liquid crystal composition
described herein disposed therebetween. In an embodiment, the
optical device has improved contrast as compared to an optical
device containing no crystal polymer. In an embodiment, the optical
device has improved switching speed as compared to an optical
device containing no liquid crystal polymer. In an embodiment, the
optical device has improved viewing-angle symmetry as compared to
an optical device containing no liquid crystal polymer.
[0052] Also provided is a method of preparing a nematic liquid
crystal composition, comprising: contacting a nematic liquid
crystal host; and between 0.01 and 5 wt % of a liquid crystal
polymer.
[0053] In an embodiment of the invention, the liquid crystal
polymer is present in the nematic liquid crystal composition at a
concentration below 1% by weight. In an embodiment of the
invention, the liquid crystal polymer is present in the nematic
liquid crystal composition at a concentration below 5% by weight.
In an embodiment of the invention, the liquid crystal polymer is
present in the nematic liquid crystal composition at a
concentration below 0.1% by weight. In an embodiment of the
invention, the liquid crystal polymer is present in the nematic
liquid crystal composition at a concentration below 0.05% by
weight. In an embodiment, n in the polymer backbone PX is an
integer from 50 to 5,000. In an embodiment of the invention, the
liquid crystal polymer has a molecular weight between 30,000 g/mol
and 5,000,000 g/mol and all intermediate values and ranges therein.
In an embodiment of the invention, the liquid crystal polymer has a
molecular weight between 30,000 g/mol and 50,000 g/mol. In an
embodiment of the invention, the liquid crystal polymer has a
molecular weight between 1,000,000 g/mol and 3,000,000 g/mol.
[0054] The liquid crystal polymer used in the liquid crystal device
can be either surface-active or bulk-active, or may have some
combination of effects. The number of chains required to confer a
surface-active effect is small as compared to a bulk-active effect.
This allows use of concentrations from 0.1% down to 0.01 wt %
polymer. Higher concentrations of dopants can also be used.
[0055] As used herein, when the liquid crystal polymer is "soluble"
or "solvated" in the nematic liquid crystal host, this means that
at least a portion of the liquid crystal polymer is solvated by the
host. In an embodiment, the liquid crystal polymer is soluble in
the nematic liquid crystal host. In an embodiment, the liquid
crystal polymer is soluble in the nematic liquid crystal host at
some temperatures and not at other temperatures. In an embodiment,
the liquid crystal polymer is reversibly soluble in the host. As
used herein, "soluble liquid crystal polymer" and other forms of
the phrase means the liquid crystal polymer forms a homogeneous
composition of host and liquid crystal polymer and there are not
phase separated layers or portions thereof. In an aspect of the
invention, the liquid crystal polymers of the invention are soluble
liquid crystal polymers. At least a portion of the liquid crystal
polymer is solvated by the host at least under some temperature and
concentration conditions. In the invention, the association between
the liquid crystal polymer and host is a physical association, not
chemical bonding between the liquid crystal polymer and host. In an
aspect of the invention where there are no end groups, there is no
physical crosslinking between liquid crystal polymer groups. In an
embodiment, there is physical crosslinking between liquid crystal
polymer groups.
[0056] As used herein "core" refers to a central portion of a
mesogen that contributes to important attributes (including but not
limited to shape, size, polarizability, dipole magnitude and dipole
orientation). In an embodiment, a mesogen M includes a core having
one or more six membered aromatic or nonaromatic rings which can
include one or more heteroatoms in the rings and one or more
substituents, including alkyl, alkoxy and halogen and one or more
tails, including the structures described herein and alkylsilane,
perfluoroalkylsliane, and silylfluoro tails.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] FIG. 1 shows that in a Vertically Aligned Nematic (VAN) cell
with no applied field, the liquid crystal molecules (rod shaped)
are oriented perpendicular to the plane of the glass plates,
sandwiched between crossed polarizers that cause the cell to appear
dark (left). When an electric field is applied, the liquid crystal
rotates to maximize its dipole in the direction of the electric
field, producing the bright state of the cell (right). With zero
pretilt (top, left), the liquid crystals can rotate in any
azimuthal direction, significantly lengthening the rise time. A
slight pretilt (lower, left) dramatically improves the rise
time--as observed with the polymer dopant described here.
[0058] FIG. 2 illustrates the traditional polymer-stabilized VA LCD
manufacture (top) involves costly electrode fabrication and
expensive, time-consuming damaging UV irradiation that are avoided
entirely in this approach using soluble polymers (bottom). The
system described here has short processing times, in some examples
as short as 10 minutes. The concentration of dopant and time used
for the "controlled cooling step" can reduce the processing time
further.
[0059] FIG. 3 shows conoscopic measurements of the pure VA liquid
crystal (MLC6886) in the left-hand column, and 0.25 wt % Polymer 5
(LCV20137) in MLC6886 (annealed at 8V, then cooled at 5.degree.
C./min at 8V) in the right-hand column, measured in an unrubbed
with 0V to 6V applied AC voltage at 1 kHz. The numbers in the
right-hand columns represent brightness, units are Cd/m.sup.2. When
polymer is added, the threshold voltage remains between 2V and 4V,
and at 4V the switching is more uniform and symmetrical than that
of the pure VA liquid crystal.
[0060] FIG. 4 shows the voltage-transmittance data for 0.25 wt %
Polymer 5 (LCV21037) in an unrubbed cell.
[0061] FIG. 5 shows the voltage-transmittance data for 0.25 wt %
Polymer 5 (LCV21037) and 0.25 wt % Polymer 6 (LCV20141) in unrubbed
cells.
[0062] FIG. 6 shows the voltage-transmittance data for 0.1 wt %
Polymer 7 (LCV20162) in rubbed and unrubbed cells.
[0063] FIG. 7 shows the voltage-transmittance data for 0.1 wt % and
0.25 wt % Polymer 7 (LCV20162) in a rubbed cell.
[0064] FIG. 8 shows the rise time data of pure VA liquid crystal
MLC6886 and VA LC with 0.25 wt % Polymer 5 (LCV20137).
[0065] FIG. 9 shows the fall time data of pure VA liquid crystal
MLC6886 and VA LC with 0.25 wt % Polymer 5 (LCV20137).
[0066] FIG. 10 shows the rise and fall time data of pure VA liquid
crystal MLC6886 and VA liquid crystal with 0.25 wt % Polymer 6
(LCV20141).
[0067] FIG. 11 shows the rise and fall time data of pure VA liquid
crystal MLC6886 and VA liquid crystal with 0.25 wt % Polymer 6
(LCV20141).
[0068] FIG. 12 shows temperature degradation data for 0.1 wt %
Polymer 7 (LCV20162) in MLC6886 in rubbed and unrubbed cells.
[0069] FIG. 13 shows the voltage-transmittance data for and 0.25 wt
% LCV20141 in a rubbed cell in MLC6886.
[0070] FIG. 14 shows the voltage-transmission curve for 0.1 wt %
LCV20141 in MLC6886.
[0071] FIG. 15 shows the voltage-transmission curve for 0.1 wt %
and 0.25 wt % LCV20162 in MLC6886.
[0072] FIGS. 16-1 and 16-2 shows Contrast ratio of LCV20141--0.25
wt % (without rubbing); Contrast ratio of LCV20141--0.25 wt % (with
rubbing); Contrast ratio of LCV20141--0.1 wt % (without rubbing);
Contrast ratio of LCV20141--0.1 wt % (with rubbing).
DETAILED DESCRIPTION OF THE INVENTION
[0073] Without wishing to be bound by any particular theory, there
can be discussion herein of beliefs or understandings of underlying
principles or mechanisms relating to the invention. It is
recognized that regardless of the ultimate correctness of any
explanation or hypothesis, an embodiment of the invention can
nonetheless be operative and useful.
[0074] In general, the terms and phrases used herein have their
art-recognized meaning, which can be found by reference to standard
texts, journal references and contexts known to those skilled in
the art. The definitions are provided to clarify their specific use
in the context of the invention.
[0075] As used throughout the present description, the expression
"a group corresponding to" or a "group" an indicated species
expressly includes a radical, including monovalent, divalent and
polyvalent radicals for example, an aromatic or heterocyclic
aromatic radical, of the groups listed provided in a covalently
bonded configuration, optionally with one or more substituents,
including but not limited to electron donating groups, electron
withdrawing groups and/or other groups.
[0076] As used herein, "alkyl" groups include straight-chain,
branched and cyclic alkyl groups. Alkyl groups include those having
from 1 to 30 carbon atoms. Alkyl groups include small alkyl groups
having 1 to 3 carbon atoms. Alkyl groups include medium length
alkyl groups having from 4-10 carbon atoms. Alkyl groups include
long alkyl groups having more than 10 carbon atoms, particularly
those having 10-30 carbon atoms. An alkoxy group is an alkyl group
that has been modified by linkage to oxygen and can be represented
by the formula R--O and may also be referred to as an alkyl ether
group. Examples of alkoxy groups include, but are not limited to,
methoxy, ethoxy, propoxy, butoxy and heptoxy. Alkoxy groups include
substituted alkoxy groups wherein the alky portion of the groups is
substituted as provided herein in connection with the description
of alkyl groups. As used herein MeO-- refers to CH.sub.3O--.
[0077] Aryl groups include groups having one or more 5- or 6-member
aromatic or heteroaromatic rings. Heteroaryl groups are aryl groups
having one or more heteroatoms (N, O or S) in the ring. Aryl groups
can contain one or more fused aromatic rings. Heteroaromatic rings
can include one or more N, O, or S atoms in the ring.
Heteroaromatic rings can include those with one, two or three N,
those with one or two O, and those with one or two S, or
combinations of one or two or three N, O or S. Aryl groups are
optionally substituted. Substituted aryl groups include among
others those which are substituted with alkyl or alkenyl groups,
which groups in turn can be optionally substituted. Specific aryl
groups include phenyl groups, biphenyl groups, pyridinyl groups,
and naphthyl groups, all of which are optionally substituted.
Substituted aryl groups include fully halogenated or
semihalogenated aryl groups, such as aryl groups having one or more
hydrogens replaced with one or more fluorine atoms, chlorine atoms,
bromine atoms and/or iodine atoms. Substituted aryl groups include
fully fluorinated or semifluorinated aryl groups, such as aryl
groups having one or more hydrogens replaced with one or more
fluorine atoms.
[0078] Optional substitution of any group includes substitution
with one or more of the following substituents: halogen, --CN
groups, --OCH.sub.3, --OCF.sub.3, --CFH.sub.2, --CF.sub.2H,
--CF.sub.2CF.sub.3, --CH.sub.2CF.sub.3, CH.sub.3, NO.sub.2,
CH.sub.2R, CH.sub.2OR, where R is a C1-C3 alkyl, and other
substituents known in the art.
[0079] Deuterium can be substituted for any H in the polymer
backbone or spacer or mesogenic side groups.
[0080] As used herein, the term "halo" or "halogen" refers to a
halogen group such as a fluoro (--F), chloro (--Cl), bromo (--Br)
or iodo (--I).
[0081] As is customary and well known in the art, hydrogen atoms in
the formulas shown herein are not always explicitly shown.
[0082] It should be noted that as used herein and in the appended
claims, the singular forms "a", "an", and "the" include plural
reference unless the context clearly dictates otherwise. Thus, for
example, reference to "an item" includes a plurality of such items
and equivalents thereof known to those skilled in the art, and so
forth. As well, the terms "a" (or "an"), "one or more" and "at
least one" can be used interchangeably herein. It is also to be
noted that the terms "comprising", "including", and "having" can be
used interchangeably.
[0083] As to any of the groups described herein which contain one
or more substituents, it is understood, that such groups do not
contain any substitution or substitution patterns which are
sterically impractical and/or synthetically non-feasible. In
addition, the compounds of this invention include all
stereochemical isomers arising from the substitution of these
compounds.
[0084] The compounds of this invention may contain one or more
chiral centers. Accordingly, this invention is intended to include
racemic mixtures, diasteromers, enantiomers and mixture enriched in
one or more steroisomer. The scope of the invention as described
and claimed encompasses the racemic forms of the compounds as well
as the individual enantiomers and non-racemic mixtures thereof.
[0085] The compounds and formulas of the invention may be used in
liquid crystal display devices as known in the art. Methods of
preparing and using liquid crystal display devices, including
preparation and use of cells is well known in the art.
[0086] The invention is further detailed in the Examples, which are
offered by way of illustration and are not intended to limit the
scope of the invention in any manner.
[0087] Instead of in situ polymerization, a polymer additive that
is soluble in the VAN is used here. Specifically, a liquid crystal
polymer (LCP), i.e., a polymer that includes a mesogen group and
can undergo the change in orientational order along with the LC
host (solvent) is used. For a chosen LC host, a mesogen group can
be designed to confer solubility in the LC phase(s) using the
methods described here. In nematic solvents, small quantities of
polymer have a large effect on the switching speed.
[0088] Liquid crystal polymers with molecular weight ranging from
30,000 g/mol to 5,000,000 g/mol are particularly useful in separate
embodiments. A shorter polymer gives rise to the desired effects
but this would require more polymer, making the use less
economical. The longer the polymer, the less soluble it is in the
VAN host and the polymer may undergo phase separation. The optimal
molecular weight depends upon variables that include the chemical
structure of the mesogens and the composition of the VAN host.
[0089] In an embodiment, a liquid crystal polymer tested had a
molecular weight of about 1.2 Million g/mol (a degree of
polymerization of about 900 repeat units). In an embodiment, liquid
crystal polymers described here have about 888 repeating units. In
an embodiment, liquid crystal polymers described here have about
900 repeating units.
[0090] In an embodiment, liquid crystal polymers described here
have about 2000 repeating units. It is to be understood that when
the number of repeating units is specified in a particular
structure, the number shown can be replaced with another number and
a compound having the resulting structure is intended to be
included in the description to the same extent as if it were
specifically drawn. For example, where a specific structure
indicates 888 repeating units in a polymer backbone, there can be
900 or 2000 repeating units in that polymer backbone and all those
resulting embodiments are intended to be included in this
description.
[0091] In an aspect of the invention, portions of the liquid
crystal polymer are not cross-linked with other portions of the
liquid crystal polymer or other liquid crystal polymers. In an
aspect of the invention, the polymer backbone is not a polyoxetane.
In an aspect of the invention, the polymer backbone is
polyethylene. In an aspect of the invention, the polymer backbone
is polybutadiene. In an aspect of the invention, the composition of
any portion of any liquid crystal polymer described herein can be
combined with the composition of another portion of the liquid
crystal polymer to form a different liquid crystal polymer which is
intended to be disclosed individually to the extent as if it were
shown explicitly, for the purpose of inclusion or exclusion in a
claim. For example, any group provided herein as PX can be combined
with any spacer W and any mesogen M described to form a liquid
crystal polymer which is useful in the invention, even if the
combination is not explicitly shown.
[0092] The materials and devices of the invention do not contain
"microdomains" of polymer interspersed with liquid crystals.
Rather, the materials and devices of the invention comprise liquid
crystal with polymer solubilized by the liquid crystal. The liquid
crystal polymer of the invention is compatible and at least
substantially homogeneous with the liquid crystal host.
[0093] In the compounds and methods of the invention, the liquid
crystal polymer is not polymerized after contact with the nematic
liquid crystal host, but is polymerized before contact with the
nematic liquid crystal host.
[0094] As used herein, "dissolve" or "soluble" when referring to
the liquid crystal polymer of the invention and liquid crystal host
means the liquid crystal polymer does not phase separate from the
liquid crystal host. Therefore, the liquid crystal polymer can
undergo the change in orientation order along with the liquid
crystal host.
[0095] As used herein, "single bond" means that two groups are
directly attached to each other. For example, when a ring is
attached to a substituent with a single bond, there are no
intervening groups between the ring and the substituent.
[0096] As used herein, the use of a line coming off of a
substituent when used as a portion of a molecule is standard in the
art and indicates that there is another substituent attached, not
necessarily that there is a carbon unit terminating. For example,
in the group
##STR00039##
the line attached to the phenyl ring does not mean there is a
terminal --CH.sub.3 group attached or a --CH.sub.2-- linker unless
those interpretations are consistent with the chemical usage, but
rather the group is attached to another group in the molecule. In
the group
##STR00040##
the two lines terminating the repeating unit are intended to be a
carbon unit (--CH.sub.3 groups) and the line exiting the repeating
unit vertically is intended to indicate attachment to another
group. This usage is standard in the art.
[0097] In an embodiment of the invention, the liquid crystal
polymers of the invention are not copolymers or block copolymers,
and have only one polymeric backbone group, generally designated as
"PX" in an embodiment. A repeating unit in a spacer group is not
considered a polymer in the context of distinguishing the molecules
here from copolymers or block copolymers.
1. Vertically Aligned Nematic (VAN) Technology
[0098] Vertically aligned (VA, also known as vertical alignment)
displays have high contrast because the liquid crystal is almost
completely vertically aligned (parallel to the path of the light,
perpendicular to the glass plates) at zero voltage, giving the cell
an excellent dark state under crossed polarizers (FIG. 1, left).
More specifically, a VAN cell uses a special nematic liquid
crystal, referred to as a "negative delta E" nematic (because the
dielectric constant along the short axis of the liquid crystal
molecule is larger than along the long axis). "Negative delta
epsilon" generally refers to a material property (i.e., of a bulk
material), usually describing a mixture of small molecules that
forms a liquid crystal with negative dielectric anisotropy (i.e.,
that have "delta epsilon" less than zero). As used herein, the term
"negative delta epsilon" is used to also describe mesogenic groups
that have a molecular dipole transverse to the long axis of the
group.
[0099] "Delta E" and "delta epsilon" are used interchangeable
herein and indicate the dielectric anisotropy.
[0100] When a voltage is applied (typically a 1 kHz sine wave), the
liquid crystal molecules reorient such that their dipoles rotate
toward the direction of the electric field (i.e., their molecular
axes rotate toward being parallel to the glass plates), resulting
in the bright state (FIG. 1, right, note arrows labeled "dipole"
and "E").
[0101] Scheme 1 shows the chemical structures of some examples of
mesogens useful in the invention. In some of the examples below,
the electron withdrawing character of fluorine is used to create a
transverse dipole by placing fluorine atoms asymmetrically on the
rings that lie along the long-axis of the molecules.
##STR00041##
[0102] On a molecular level, the key to VAN is the orientation of
the dipole orthogonal to the long axis of the molecule. It is a
delicate matter to incorporate such molecules in a liquid crystal,
because these molecules tend to have high melting temperatures. For
example, the structures shown in Scheme 1 have strongly negative
.DELTA..di-elect cons. ranging from -2.7 for 3 to -8.6 for 8.
However, all of them are crystalline solids at room temperature;
their melting points range from 4500 for 1 to 99.degree. C. for 7.
Furthermore, if the pure compound has a nematic phase, it tends to
have high viscosity coefficients (i.e., slow response). Eutectic
mixtures have been developed that maintain nematic order over a
broad range of temperature near ambient conditions and compromise
between having highly negative .DELTA..di-elect cons. and having
low viscosity. It is important that any polymer dopants used
dissolve in negative delta E nematic mixtures without slowing their
switching response.
[0103] The transverse dipoles on the individual molecules give the
nematic phase an unusually high polarizability in the plane
orthogonal to the director. While VA nematics depend upon molecules
that possess a transverse dipole, the nematic phase does not have a
transverse dipole until the electric field is applied. In the
absence of a field, the dipoles of the individual molecules are
symmetrically distributed about the "director" (the direction of
the average orientation of the long axis of the molecules). When an
electric field is imposed in the plane orthogonal to the director,
it breaks symmetry and the orientation distribution of transverse
dipoles becomes biased along the direction of the applied
field.
[0104] One of the challenges intrinsic to vertical alignment is
that the usual electrode arrangement (on opposite sides of the
liquid crystal) applies an electric field orthogonal to the cell
(as shown in FIG. 1 by the arrow "E")--parallel to the director. If
the director is perfectly homeotropically aligned, the applied
field does not couple to the high polarizability plane of the
negative delta E nematic (FIG. 1, top). Consequently, switching is
slow.
[0105] Current approaches to improve the response time involve
special alignment layers and complex patterns of electrodes in the
display structure itself. Surface layers that orient the director
slightly away from the cell normal (i.e., introduce a slight
pretilt) improve switching speed by dictating a uniform "fall
direction" (FIG. 1, bottom). However, the pretilt must be kept
small to maintain the very dark "off state" that is a hallmark of
VAN-LCDs. Often the pretilt is combined with complicated electrode
patterning, nanofabricated protrusions, or complex and costly
driving schemes to achieve acceptable response time. In addition to
the added production cost required for these extra fabrication
steps, the common side effect of these attempts is loss of contrast
due to light leakage.
[0106] In prior methods to use polymers in VAN, the polymerization
is performed in the LC cell: monomers are introduced into the
active medium of the display and polymerized in situ, either on the
surface or throughout the bulk by exposing the cell to ultraviolet
(UV) light for a specific duration. The motivation for including
this costly step traces back to a discovery in 2007: the switching
speed of a VA display can be significantly improved by
photopolymerizing a small amount of reactive monomer within the VAN
liquid crystal cell. The polymer dopants described herein
represents a major departure from previous polymer structures that
sustain a pretilt angle in VAN LCDs.
2. Polymer-Doped VA Approach
[0107] In general, the technology described here uses liquid
crystals (LCs) doped with liquid crystal polymers (LCPs). Liquid
crystal polymers (LCPs) are flexible-chain polymers that are
functionalized with mesogens. They exhibit unique properties that
arise from the coupling of the orientational order inherent in the
mesogen group to the flexible backbone of the polymer. When they
are dissolved in a small-molecule LC, liquid crystal LCPs adopt an
anisotropic conformation because the mesogen moieties couple
locally to the director of the nematic solvent, leading to a
synergistic ordering effect that has no counterpart in random coil
polymers in conventional solvents. In contrast to in-situ
polymerized gels, polymer dopants dissolve homogeneously in the
liquid crystal, giving materials with exceptional optical
uniformity. When the concentration of polymer is kept low, the
switching speed of the LC remains rapid.
[0108] FIG. 2 compares the typical PS-VA approach with the
polymer-doped VA approach described here. Instead of performing a
radical step polymerization inside the display (FIG. 2, top), this
approach uses LCPs synthesized and purified outside of the display
that are added at low concentration to the VA nematic liquid
crystal before it is loaded into the LCD (FIG. 2, bottom). As will
be further described herein, the polymer dopants described here can
dramatically improve switching speed without introducing ionic and
radical impurities produced during UV irradiation. In addition, the
polymer dopants described here can actually increase contrast. By
using polymers that dissolve uniformly in the active medium of the
display, the approach described here maintains the optical
uniformity of the LC and avoids the polymerization-induced
phase-separation that occurs during the in situ UV
photopolymerization of monomers in LCs. Very low concentrations of
polymers are sufficient: data shown here use 0.25% dopant, but as
will be apparent to one of skill in the art by a review of the
materials here, even lower concentrations or higher concentrations
can be used.
3. Liquid Crystal Polymer Design
[0109] In order to show polymeric stabilization of the polymer
dopants described here, including "negative delta E" liquid
crystals (LCs with .DELTA..di-elect cons.<0), several LCP
homopolymers having various structures were chosen and synthesized
having different molecular weights and linking groups of
cyanobiphenyl side groups (Polymers 1, 2 and 3 in Scheme 2) as well
as phenylpyrimidine side groups with different linking groups
(Polymers 4 and 5 in Scheme 2) and 2,3 difluorophenyl
bicyclohexylgroup attached with a siloxane linking group (Polymer 6
in Scheme 2) were synthesized and tested. A targeted selection of
ABA coil-LCP-coil triblock copolymers were also synthesized and
tested.
[0110] Mesogens and other components designed to improve solubility
and to test the effect of their dielectric anisotropy were
synthesized using polymer analogous chemistry. Polymer analogous
chemistry using separately synthesized mesogens and identical
polymer backbones enable a determination of the effect of mesogen
structure by holding the polymer backbone length fixed. By
selecting the mesogen structure, the miscibility of the LCP is
controlled and the structure function relationship between the
dielectric anisotropy and the nematic-polymer gel matrix was
explored. The polymers synthesized allowed the effects of dipole
placement, dipole strength, and linking (spacer) groups (i.e.
siloxane vs. thiol) connecting the side group to the polymer
backbone to be isolated.
##STR00042##
[0111] The cyanobiphenyl side groups (polymers 1, 2 and 3 in Scheme
2) have dielectric anisotropy (.DELTA..di-elect cons.) on the order
of +13, while the phenylpyrimidine side groups (polymers 4 and 5 in
Scheme 2) should have much smaller, though still positive
dielectric anisotropies, approximately +1 or +2. The fluorinated
phenyl bicyclohexyl side group, on the other hand, was designed to
have a negative dielectric anisotropy (.DELTA..di-elect
cons..apprxeq.-4).
[0112] Spacer length affects both the solubility of the polymer and
the alignment of the pendant mesogens, so it is an important
variable in tuning of the LCP dopants. Altering the alkyl spacer
length involves the same chemical reactions, simply exchanging one
of the starting materials. This modification is well-known and
understood by one of ordinary skill in the art.
[0113] The mesogenic groups of both polymers 5 and 6 (Scheme 2) had
alkyl spacers that were 7 or 8 carbons long, and were attached to
the polymer backbone via siloxane linking groups. Polymer analogous
chemistry was used to create polymers with exactly matched backbone
length so that the effect of the side group could be determined
definitively. Specifically, mesogenic groups are attached to the
pendant vinyl groups of an anionically synthesized prepolymer, 1,
2-polybutadiene, using platinum catalyzed hydrosilation.
[0114] The longer the polymer chain length of the LCP, the more
potent its effect is expected to be on the alignment behavior of
the LC solvent. Therefore a much longer polymer chain will confer
the desired material property enhancements at a much smaller
concentration of polymer. This will allow use of even less of the
polymer additive per display screen, for example.
[0115] Based on the excellent characteristics of the LCP bearing 2,
3-difluorophenyl bicyclohexyl side groups attached to a 107 kg/mol
1, 2-polybutadiene prepolymer backbone (compound 6 in Scheme 2),
the same side group can be used to synthesize a series of higher
molecular weight polymers using art-known procedures.
[0116] Other examples of negative delta E LC fragments (in general
mesogens and spacers) that can be attached to a polymer backbone
using methods known in the art and described herein to form liquid
crystal polymers are shown in Scheme 3. In this Scheme, R=terminal
alkenyl or silyl alkyl or alkoxy tail having from 1 to 20 carbon
atoms.
##STR00043##
[0117] Table 1 shows the physical properties of the structures in
Scheme 1 as stable nematic liquid crystals for use in formulating
high negative delta E mixtures.
TABLE-US-00001 TABLE 1 No. Mesophases T.sub.NI, extr.
.DELTA..epsilon. .DELTA.n .gamma.I 1 C 49 N (12.9) I 16.5 -6.2
0.099 110 2 C 79 S.sub.B (78) N 184.5 I 174.4 -5.9 0.096 413 3 C 67
N 145.3 I 139.0 -2.7 0.095 218 4 C 61 N 129.9 I 96.4 -4.6 0.087 549
5 C 80 N 173.3 I 187.7 -5.9 0.156 233 6 C 80 I 44.0 -7.3 0.133 637
7 C 99 I 18.1 -7.1 0.086 136 8 C 85 I 49.4 -8.6 0.085 142
[0118] Table 2 shows some exemplary mesogens useful in the
compositions, methods and devices described here. As will be
apparent by a review of the materials herein and using synthesis
methods known in the art, the mesogens can be coupled or bonded to
the polymer backbone and the spacer (if used) using conventional
synthetic methods. In an example, one coupling method is to add the
vinyl group or aldehyde group shown in the structures to
tetramethyldisiloxane, or its diethylsilane counterpart and then to
the polymer using the methods described herein or known to the art.
Some of the groups listed (LCV20140, 20143 and 20167 for example)
have positive delta E.
TABLE-US-00002 TABLE 2 Item No. Structure Comments LCV20142A
##STR00044## LCV20143 ##STR00045## LCV 20163 ##STR00046## Negative
.DELTA..epsilon. Only different from LCV20154 in alkyl spacer
LCV20154 ##STR00047## Negative .DELTA..epsilon. Only different from
LCV20163 in alkyl spacer LCV20138 ##STR00048## Neutral
.DELTA..epsilon. LCV20140 ##STR00049## Positive .DELTA..epsilon.
LCV20167 ##STR00050## Isolates for longer alkyl tail in side-on
LCV20147 ##STR00051## Negative .DELTA..epsilon. Matched Set with
LCV20167 LCV20168 ##STR00052## Very Negative .DELTA..epsilon.
LCV20383 ##STR00053## LCV20385 ##STR00054## LCV20384 ##STR00055##
LCV20142 ##STR00056## Negative .DELTA..epsilon.
[0119] Scheme 4 shows exemplary synthetic schemes to prepare
silane, disilane and trisilane structures where ArO-- in the
synthetic schemes is the
##STR00057##
group shown. These silane structures can be attached to a polymer
backbone using methods known in the art and described herein. The
mesogen shown can be replaced with other mesogens, as known in the
art.
##STR00058##
[0120] Scheme 5 shows mesogens designed to increase their
orientational coupling to the small molecule VAN host by (top)
increasing the length and rigidity of the mesogen's long axis and
(bottom), increasing the transverse dipole of the mesogens. These
groups are useful in the methods of the invention and can be
attached to polymer backbones and other spacers as described here
and known in the art. The number of repeating units in the groups
shown below is any suitable number, for example an integer from 0
to 15.
##STR00059##
[0121] The fragments and molecules shown here can be attached to
the polymer backbone and spacer using synthetic methods known in
the art. Table 3 shows additional examples of liquid crystal
polymers that can be used in the compositions, methods and devices
described here. The structures in Table 3 show mesogens attached to
specific linkers and specific polymer backbones. As will be
apparent, the linkers and polymer backbones can have different
structures and still function in the compositions, methods and
devices described here. For example, the number of repeating units
in the polymer may vary. All such modifications are intended to be
included in the specification to the extent as if they were
specifically listed.
TABLE-US-00003 TABLE 3 Item No. Structure Comments A ##STR00060##
Siloxane Linked Negative .DELTA..epsilon. From LCV20154 B
##STR00061## Siloxane Linked Negative .DELTA..epsilon. From
LCV20163 C ##STR00062## Siloxane Linked Negative .DELTA..epsilon. D
##STR00063## Thioether Linked Negative .DELTA..epsilon. E
##STR00064## Siloxane Linked Neutral .DELTA..epsilon. From LCV20138
F ##STR00065## Siloxane Linked Negative .DELTA..epsilon. From
LCV20147 G ##STR00066## Silane Linked Negative .DELTA..epsilon.
From LCV20164 H ##STR00067## LCV 20162 (Also Designated as Polymer
7) I ##STR00068## Siloxane Linked Very Negative .DELTA..epsilon.
From LCV20168 J ##STR00069##
TABLE-US-00004 TABLE 3A Item No. Structure AA ##STR00070## BB
##STR00071## CC ##STR00072## DD ##STR00073## EE ##STR00074## FF
##STR00075## GG ##STR00076## HH ##STR00077## II ##STR00078## JJ
##STR00079##
[0122] As will be understood by one of ordinary skill in the art,
the actual number of repeating units in a polymer or oligomer is
difficult to determine exactly. Therefore, when a particular number
is presented for the number of repeating units, it is understood
that all values .+-.10% are included, and other ranges as well as
other values within the ranges specified herein.
Hosts
[0123] As will be apparent to one of ordinary skill in the art, any
useful nematic liquid crystal host can be used in the methods of
this invention. Some hosts include the following:
TABLE-US-00005 TABLE 4 Negative Delta Epsilon Nematic Liquid
Crystal Host MX40076 Concentration # Compound (wt %) 1 ##STR00080##
16 2 ##STR00081## 13 3 ##STR00082## 7 4 ##STR00083## 7 5
##STR00084## 13 6 ##STR00085## 44
[0124] The phase diagram tollows:
I 99 N<-20 X
Eperp=6.9
Epara=3.5
Delta E=-3.4
[0125] Negative delta E nematic LC mixtures are also commercially
available, for example from Merck including those mixtures shown
below.
TABLE-US-00006 TABLE 5 Rot. Tc clearing Viscosity Birefringence K11
K33 Vth ID point (.degree. C.) (mPas) Delta n Delta E (pN) (pN) (V)
Appl. MLC6608 90 186 0.0830 -4.2 16.7 18.1 2.17 MLC6609 91.5 162
0.0777 -3.7 17.2 17.9 2.33 MLC6610 79.5 148 0.0996 -3.1 14.6 16.5
-- MLC6886 75 146 0.0899 -3.8 13.8 14.8 -- MLC3006 75 104 0.0998
-3.0 -- -- -- TV MLC3008 85 230 0.01001 -4.9 -- -- -- mobile
ZLI2806 101 270 0.0437 -4.8 -- -- 1.90 MLC7029 95 175 0.1265 -3.6
16.1 15.0 2.14
4. Synthesis Methods
Synthesis of Vinyl-Terminated Cyanobiphenyl Side Group for Siloxane
Coupling
[0126] A vinyl-terminated, cyanobiphenyl side group with a four
carbon alkyl spacer was synthesized by standard ether chemistry as
follows: 4-cyano-4'-hydroxybiphenyl (HCB) and a bromoalkene,
4-bromobut-1-enel, and oven-dried Cs.sub.2CO.sub.3 were dissolved
in 40 mL dimethyl formamide and stirred at room temperature
overnight. When the reaction was complete (as monitored by thin
film chromatography), the reaction mixture extracted three times
with dichloromethane and the combined organic extracts were washed
with water, then dried with MgSO.sub.4. The solvent was evaporated
and the crude product was recrystallized in hot 95% ethanol,
resulting in analytically pure white crystals of
4-cyano-4'-(3-butenoxy)-biphenyl (CBV4).
Siloxane Coupling and 1,2 Polybutadiene Functionalization of
Cyanobiphenyl Side Group
[0127] A siloxane linking group is added to the alkene-terminated
cyanobiphenyl mesogens by hydrosilation as follows: A tenfold
excess of 1,1,3,3-tetramethyldisiloxane (TMDS), CBV4 and one drop
of platinum catalyst (PC072 platinum divinyl complex in xylene)
were dissolved in 20 mL anhydrous toluene, filled with dry argon
gas and stirred at 50.degree. C. for 1 day. When the reaction was
complete as monitored by thin layer chromatography, the solvent and
excess TMDS were evaporated at 80.degree. C. under vacuum and the
product (SiCB4) was purified by anhydrous column chromatography
using 1:10 anhydrous ethyl acetate to anhydrous hexanes as the
mobile phase.
[0128] This siloxane-linked mesogen (SiCB4) was then immediately
attached to the pendant vinyl groups of 1,2-polybutadiene, also by
platinum catalyzed hydrosilation. The following is a representative
synthesis of this attachment to 1,2, polybutadiene: Polybutadiene a
three-fold excess of freshly purified SiCB4 and one drop of
platinum catalyst (PC085, platinum cyclovinyl complex in
vinylmethylsiloxanes) were dissolved in 15 mL of anhydrous
tetrahydrofuran (THF) under inert atmosphere and then heated at
50.degree. C. for four days. When the reaction was complete, as
monitored by .sup.1H NMR, the catalyst was quenched by adding
excess styrene and stirring overnight at 50.degree. C. and the
polymer (polymer 1, and 2) was then purified by evaporating all but
the last 5 mL of solvent under vacuum, followed by repeated
precipitation from THF solutions with cold methanol containing 10
ppm BHT, Before the final precipitation, a solution of
approximately ten percent polymer in THF is passed through a 0.45
.mu.m syringe filter, then concentrated and precipitated again.
After this final precipitation the solid polymer is then dried to
constant weight under vacuum at room temperature.
Synthesis of Vinyl-Terminated Phenyl Pyrimidine Side Group for
Siloxane Coupling
[0129] A vinyl-terminated phenyl pyrimidine side group was
synthesized from 4-(5-decylpyrimidin-2-yl)phenol for siloxane
coupling to 1,2 polybutadiene using standard ether chemistry as
follows: 4-(5-decylpyrimidin-2-yl)phenol (1.93 grams, 6.15 mmols),
a bromoalkene (7-bromohept-1-ene, 1.22 mL, 8 mmol) and oven-dried
Cs.sub.2CO.sub.3 (2.56 grams, 8 mmol) were stirred at room
temperature in 40 mL of dimethyl formamide overnight, resulting in
near-quantitative conversion to the ether (Scheme 6), as monitored
by thin layer chromatography. The reaction mixture was extracted
three times with 50 mL of dichloromethane. The organic extracts
were washed three times with water and dried with MgSO.sub.4. The
crude product was recrystallized in hot 95% ethanol, resulting in
analytically pure white crystals of
5-decyl-2-(4-(hept-6-enyloxy)phenyl)pyrimidine,
enyloxy)phenyl)pyrimidine, or C7PPC10V, (1.69 g, 66.0% overall
yield).
##STR00086##
Siloxane Coupling and 1,2 Polybutadiene Functionalization of Phenyl
Pyrimidine Side Group
[0130] A siloxane linking group is added to the alkene-terminated
phenyl pyrimidine mesogens by hydrosilation (Scheme 7) as follows:
A fivefold excess of 1,1,3,3-tetramethyldisiloxane (TMDS) (3 mL, 17
mmol), C7PPC1V (1.69 g, 3.25 mmol) and one drop of platinum
catalyst (PC072 platinum divinyl complex in xylene) were dissolved
in 20 mL anhydrous toluene, filled with dry argon gas and stirred
at 50.degree. C. for 2 days. This reaction was monitored by thin
layer chromatography, and, when completed, the solvent and excess
TMDS were evaporated at 80.degree. C. under vacuum and the product
(SiC7PPC10) was purified by anhydrous column chromatography.
##STR00087##
[0131] The siloxane-linked mesogen was then attached to the pendant
vinyl groups of 1,2-polybutadiene, also by platinum catalyzed
hydrosilation. 107 kg/mol Polybutadiene (0.035 g, 0.6 mmols) was
dissolved in 10 mL of anhydrous tetrahydrofuran (THF) under inert
atmosphere. A one-and-a-half-fold excess of freshly purified
SiC7PPC10 and one drop of platinum catalyst (PC085, platinum
cyclovinyl complex in vinylmethylsiloxanes) and the mixture was
heated at 50.degree. C. for four to six days. Reaction progress was
monitored by .sup.1H NMR. When the reaction was complete it was
quenched with excess styrene and stirred at 50.degree. C. overnight
and the polymer (polymer 5) was then purified by evaporating all
but the last 5 mL of solvent under vacuum, followed by repeated
precipitation from THF solutions with cold methanol containing 10
ppm BHT, Before the final precipitation, a solution of
approximately ten percent polymer in THF is passed through a 0.45
.mu.m syringe filter, then concentrated and precipitated again.
After this final precipitation the solid polymer is then dried to
constant weight under vacuum at room temperature.
Synthesis of Benzoyl-Protected Thiols, for Thiol-Ene Coupling
[0132] Benzoyl-protected thiols were synthesized from
4-(5-decylpyrimidin-2-yl)phenol for thiol-ene coupling to 1,2
polybutadiene. 4-(5-decylpyrimidin-2-yl)phenol (1.89 grams, 6.05
mmols), 1-bromo-6-chloro-hexane (1.57 g, 8 mmol) and CsCO.sub.3
(2.56 grams, 8 mmols) were stirred at room temperature in 40 mL of
dimethyl formamide overnight, resulting in near-quantitative
conversion of the ether (Scheme 8). The reaction mixture was
extracted three times with 50 mL of dichlormethane. The organic
extracts were washed three times with water and dried with
Mg.sub.2SO.sub.4. The crude product was recrystallized in hot 95%
ethanol, resulting in analytically pure white crystals (1.92 g;
76.56 overall yield) of
2(4-(5-cholohexyloxy)phenyl)-5-decylpyridine.
[0133] 2(4-(5-cholohexyloxy)phenyl)-5-decylpyridine was then
reacted with thiobenzoic acid (0.6 g, 4 mmol) and sodium
bicarbonate (0.35 g, 4 mmol) and stirred 40.degree. C. overnight
(Scheme 8). The reaction mixture was extracted with ethyl acetate
three times, washed three times with water, and dried with
Mg.sub.2SO.sub.4. The crude pink solid was then recrystallized in
hot 95% ethanol to give analytically pure pink needle-like crystals
(2.2045, 85.1% yield).
##STR00088##
Thioester Cleavage and 1,2,-Polybutadiene Functionalization.
[0134] The thioesters in the benzoyl-protected thiols were cleaved
and the resulting thiol terminated mesogens were coupled to 1,2
polybutadiene by radical initiated thiol-ene coupling. The
thioester (1 g, 1.9 mmol) was first dissolved in 25-75 mL DMF with
hydrazine monochloride (0.13 g, 1.9 mmol) and sodium acetate (0.13
g 1.9 mmol). The reaction mixture was purged with argon for 10
minutes and stirred for 6 hours at room temperature. The thiol
product was extracted into 30 mL of chloroform, washed 3 times with
water and transferred into a flask containing 1,2 PB (0.03 g, 0.6
mmol) and AIBN (50 mg), mmol) dissolved in 10 mL of chloroform.
This mixture was then degassed in 2 freeze-pump-thaw cycles and
then allowed to react at 55.degree. C. for overnight. The final
polymer product (4) was then purified by evaporating all but the
last 5 mL of solvent under vacuum, followed by repeated
precipitation from THF solutions with cold methanol containing 10
ppm BHT, then drying to constant weight under vacuum at room
temperature.
##STR00089##
Siloxane Coupling and 1,2 Polybutadiene Functionalization of
Fluorinated Bicyclohexyl Phenyl Side Groups
[0135] The compound having structure 6 in Scheme 2 having a
targeted side group designed both to increase the solubility of the
polymer in the VA nematic host and to have a dipole direction and
magnitude commensurate with that of the solvent was synthesized.
The side group bicyclohexyl-2,3-difluorophenyl alkoxy was chosen
since this group performs well in high resistivity, negative delta
E NLCs used in high-end LCD HDTVs. Small molecule nematic LCs in
this class typically have .DELTA..di-elect cons. values of about
-4.4.
[0136] This synthesis of the
4-(2,3-difluoro-4-(oct-7-en-1-yloxy)phenyl)-4-fluoro-4'-propyl-1,1'-bi(cy-
clohexane) side group was carried out by first attaching an alkene
end group to 2,3-difluorophenol. (Scheme 10). This was then
lithiated at -78 C with n-Butyl lithium to afford the aryl lithium,
followed by Dropwise addition of the bicyclohexylketone. Due to
competitive deprotonation of the allylic protons in the alkene side
chain, it was critical to optimize conditions so that the formation
of the desired aryl lithium salt was maximized, while competitive
deprotonation of the allylic hydrogens on the alkene tail was
avoided, which would lead to lower yields of the desired product.
Attempted fluorination of the tertiary alcohol formed from the aryl
lithium addition to the cyclohexyl ketone resulted in dehydration
to the cyclohexene instead of the expected tertiary fluoride
However, the 2,3-difluorophenylcylohexenyl LC that was produced
still results in a useful LC alkene pendant that was then used in
the next polymerization step.
##STR00090##
[0137] The LCP using this negative delta E group was prepared by
platinum-catalyzed hydrosilation, first of the vinyl-terminated
side group, with tetramethyldisiloxane and then another
hydrosilation of the product of the first reaction with the pendant
vinyl groups of the polybutadiene backbone (Scheme 10).
[0138] The side group (0.2441 g, 0.582 mmol) was dissolved in 20 mL
anhydrous toluene along with a tenfold excess of
1,1,3,3-tetramethyldisiloxane (TMDS) (0.8 mL, 4.5 mmol, 8.times.
excess) and one drop of platinum catalyst (PC072 platinum divinyl
complex in xylene). This mixture was stirred at 50.degree. C. for 4
days, and when completed (as monitored by thin layer
chromatography), the solvent and excess TMDS are evaporated at
80.degree. C. under vacuum and the product was purified by
anhydrous column chromatography using anhydrous 10% ethyl acetate
in hexanes as the mobile phase (0.261 g, 81% yield).
[0139] The siloxane-linked mesogen was then attached to the pendant
vinyl groups of 1,2-polybutadiene, also by platinum catalyzed
hydrosilation (Scheme 10). 107 kg/mol Polybutadiene (0.0086 g) was
dissolved in 10 mL of anhydrous tetrahydrofuran (THF) under inert
atmosphere with a three-fold excess of freshly purified siloxane
terminated mesogen and one drop of platinum catalyst (PC085,
platinum cyclovinyl complex in vinylmethylsiloxanes) and the heated
at 50.degree. C. for five days. Reaction progress was monitored by
.sup.1H NMR and when completed, the reaction was quenched with
excess styrene and heated at 50.degree. C. overnight.
[0140] The polymer (6) was purified by repeated precipitation in
methanol (containing 10 ppm BHT), filtration through at 0.45 .mu.m
PTFE syringe filter, followed by solvent fractionations using a
tetrahydrofuran-methanol mixture as the good solvent and methanol
(containing 10 ppm BHT) as the poor solvent. The methanol was added
at room temperature to a solution (approximately 0.5% polymer) of
the polymer in the good solvent until the cloud point was reached.
5-15 mL of methanol was added and the cloudy solution which was
then heated to 70.degree. C. until it became clear, whereupon it
was poured into an oven-hot, insulated separatory funnel and
allowed to separate slowly, overnight, protected from air currents.
The next day, viscous syrup (composed largely of high molecular
weight polymer) sat at the bottom of the separatory funnel, and was
easily drained off, precipitated with methanol, and dried in
vacuum. The low molecular weight polymer remained in the dilute
solution (above the high molecular weight fraction in the
separatory funnel after cooling) and was recovered by evaporating
the solvent, precipitating with methanol then drying in vacuum
overnight. In the case of this polymer, two fractionations, in
series, were needed to obtain suitable, un-crosslinked
fractions.
[0141] One goal was to give the mesogen a strongly negative
dielectric anisotropy by increasing the dipole transverse to the LC
molecular axis. This allows the use of lower voltage to control
surface pre-tilt in the LC cell. The addition of the third fluorine
was expected to increase |.DELTA..di-elect cons.| from 4.4 to
approximately 5.5. In fact, measurement of the new monomer in a
nematic host afforded an extrapolated value of .DELTA..di-elect
cons.=-5.2, from a 20% concentration in a neutral nematic host.
Tetrafluoro and Hexafluoro Substituted LCs
[0142] Scheme 11 shows Synthesis of tetrafluoro and hexafluoro
substituted LCs for attachment to polymer backbone. R is shown as a
particular vinyl terminated alkyl chain but the chain length can
vary.
##STR00091##
Dimethylsilylethylenesilane Tail
[0143] In related experiments with polymers dissolved in non-VAN
LCs hosts a small amount of phase separation can occur over the
long term for some polymers. This may be due to the siloxane
linker--the least soluble part of the polymer. Therefore, a
synthetic route to change the linker not containing any Si--O bonds
such as the methylsilane to the more soluble silane group, as well
as the more soluble, and more stable, ethyl disilane group can be
used. The synthesis of dimethylsilylethylenesilane tail, shown
using a representative vinyl terminated side group: the side group
used in Polymer (1) is provided in Scheme 12.
##STR00092##
5. Cell Preparation and Characterization
[0144] Vertically aligned liquid crystal host MLC6608 and host LC
MLC6886 (T.sub.ni=75.degree. C.; .DELTA.n=0.0899; .DELTA..di-elect
cons.=-3.8, .gamma.=146 mPa s) were used for the VAN host
materials. 4-cyano-4'-hydroxybiphenyl was purchased from TCI
America and used as received. 4-(5-decylpyrimidin-2-yl)phenol was
purchased. Other materials were synthesized as described above.
Polybutadiene (98% 1,2 content) of size 1.07.times.10.sup.3 g/mol
and narrow molecular weight distribution (of polydispersity index
1.07) were synthesized. Platinum catalysts were obtained from
United Chemical Technologies in Bristol, Pa. and used as received.
Thioether linked polymer 3 was synthesized and used as received.
All other reagents were obtained at 99% purity from Sigma Aldrich
and used as received, unless stated otherwise.
[0145] .sup.1H NMR spectra were obtained using an Inova 500 MHz NMR
spectrometer, recorded in CDCl.sub.3 and referenced to
tetramethylsilane. Polymer molecular weight measurements were
obtained by gel permeation chromatography in tetrahydrofuran (THF)
at 25.degree. C. eluting at 0.9 mL/min through four PLgel 10 .mu.m
analytical columns (Polymer Labs, 10.sup.6 to 10.sup.3 .ANG. in
pore size) connected to a Waters 410 differential refractometer
detector (.lamda.=930 nm). The molecular weight measurements were
analyzed based on calibrations using polystyrene standards.
[0146] Solutions of desired concentration (for example 0.01, 0.1,
0.25, 0.5 and 1.0 weight percent) of LCP homopolymers in negative
delta E nematic liquid crystal solvents were prepared by adding
known masses of the polymers to known masses of the liquid crystal
(either MLC6608, MLC6886). The polymers were dissolved into the
host materials by repeated iterated heating to the isotropic phase
followed by centrifugation and vortex mixing.
[0147] The liquid crystal polymers were tested in test cells with
an area of 2 cm.times.2.5 cm and an approximate 4 .mu.m thickness,
with either rubbed or unrubbed alignment layers. The parameters for
the particular tests were applied to the cell as standard in the
art. The cells were manufactured by EHC, Japan, and possessed a
homeotropic alignment layer to provide vertical aligned LCs upon
filling and cooling of the sample.
[0148] The optical measurements were conducted using an
Autronic-MELCHERS "Conocontrol" Conoscope. It automatically
measures Luminance, Chromaticity, and Response time. Conoscopic
instruments are based on the conoscopic method. With the conoscopic
method the sample is located in the front focal plane of the
optical system. A cone of elementary parallel light beams is
transmitted, emitted or reflected by the sample. All light beams
that originate from the measuring spot are collected simultaneously
over a large solid angle by the optical system. The directional
intensity distribution of the cone of elementary parallel light
beams is transformed into a two-dimensional distribution of light
intensity and color. This two-dimensional distribution of light
intensity and color is called conoscopic figure. The conoscopic
figure, is generated in the rear focal plane of the optical system.
The intensity of each area element corresponds to the intensity of
one elementary parallel beam with a specific direction of light
propagation.
[0149] The light propagating parallel to the optical axis of the
conoscopic receiver forms the center of the circular pattern, i.e.
the conoscopic figure. Beams with constant angle of inclination
(.theta.) appear as concentric circles around the center. The
radius of these circles is proportional to the angle of inclination
(.theta.). Each location in the conoscopic figure corresponds to
exactly one direction of light propagation (.theta., .phi.). A
second optical system optionally projects the conoscopic figure on
a two-dimensional CCD-detector array to evaluate the spatial
intensity distribution. The spatial intensity distribution
corresponds to the directional intensity distribution of the light
emerging from the measuring spot on the sample.
6. Results
A. Solubility
[0150] The cyanobiphenyl liquid crystal polymer that tested were
not soluble in the negative delta E hosts that used (commercially
available MLC6608 and MLC6886) as model LCs for this experiment. On
the other hand, the phenylpyrimidine LC polymers (4 and 5, Scheme
2) were soluble at 0.5% and lower concentration, thus easily
soluble at the concentration of interest. It was also found that
the negative delta E LC polymer, polymer 6, was easily soluble in
the negative delta E hosts, likely due to the molecular
compatibility of the side group and the VA LC host, possessing a
bicyclohexy-2,3-difluorophenyl core. In addition, polymer LCV 20162
was also soluble at tested conditions, likely due to its
cyclohexyl-2,3-biphenyl core. However, LCV20161, which possessed a
2,3-difluoroterphenyl core, was not soluble at 0.25% concentration,
probably due to the ridged, all aromatic 3-ring core.
B. Switching Speed
[0151] The effect of the LC polymer in the response of the VA hosts
was examined using electro-optic switching conditions. The LC
response time consists of rise and fall time. The rise time is
measured when voltage is applied and the fall time is measured when
voltage is released. Both response times need to be evaluated
because they represent two different kinetic processes. One analogy
is the stretch and release an elastic band. Different LC modes and
various surface boundary conditions, of course, will have different
response times.
Switching Speed Measured in Cell with Zero Pretilt
[0152] The optical rise times of the virgin VA nematic LC (no
polymer dopant) relative to its counterparts doped with 0.25% of 5
and 6 (Scheme 2) show that the rise time is improved with the
addition of both LC polymers. It should be noted that for this
test, a simple 1 KHz 5V AC drive signal was used--in commercial VA
displays, many other techniques (e.g., overdrive schemes coupled
with lookup tables), are used to achieve more rapid rise time, so
the reported rise times are much longer than would be observed in
practice (i.e. reported in seconds rather than milliseconds).
Polymer 5 decreases the rise time by more than four and half fold,
while polymer 6 decreases the rise time by more than 8-fold. The
fall times in an unrubbed cell appear to be less
affected--decreasing slightly with the addition of polymer 5, and
increasing slightly with the addition of polymer 6.
[0153] Polymer-doped VAN cells (0.25% by weight polymer) were
cooled from the isotropic phase into the nematic phase under
applied AC voltages of 12V, starting at 80.degree. C. and cooling
to 25.degree. C. at 5.degree. C./min. Their optical rise and fall
times were measured and compared to that of the Pure VA in unrubbed
cells. Preliminary experiments using unrubbed cells demonstrated
that the polymer dopant did not interfere will filling cells and
the polymer doped LCs retained high optical quality.
Switching Speed Measured in Cell with Small Pretilt (Rubbed
Cell)
[0154] In a rubbed cell, under conditions more similar to
industrial conditions, the optical rise times of the VA nematic LC
doped with 0.25% of 6 (Scheme 2) is improved by nearly 2 fold, from
232 ms to 130 ms, by addition of the polymer dopant. In addition,
the fall time is also improved, by nearly 2-fold, from 8 ms to 4.5
ms. Polymer 5 gave qualitatively similar improvements, but not as
large as those observed for 6; therefore, pendant mesogens with
negative dielectric anisotropy (like the VA nematic host) appear
more promising for VAN dopant technology.
[0155] The dramatic decrease in rise time suggests that the LC
polymers do, indeed, increase the pretilt of the LCs, while the
decrease in the fall time suggests that the LC polymer is also
providing an anchoring condition that induces the molecules to
relax back faster.
C. Viewing Angle and Contrast
[0156] The effect of the LC polymer on the optical uniformity of
the VAN cell was characterized using conoscopic measurements as a
function of the applied AC voltage on the cell. Polymers 5 and 6
(Scheme 2) were dissolved at 0.25 wt % in the commercial VA nematic
MLC6886 and loaded into 4 pm thick test cells bearing unrubbed
alignment layers. Cells containing doped-VAN were subjected to
controlled cooling from the isotropic phase (held for 2 minutes) to
the nematic phase under application of an AC voltage at 1 kHz while
the cell was cooled from 80.degree. C. to 25.degree. C. at
5.degree. C./min. The effect of the magnitude of the imposed AC
voltage during cooling showed that the optical quality improved
when an AC voltage as low as 2V was applied (relative to a control
processed without an applied field) and that the benefit increased
as the "annealing voltage" was increased to 8V, with little further
improvement when 12V was used. Results are shown for a doped-VA
cell (containing 0.25 wt % of 5) prepared by cooling under an 8V AC
applied field.
[0157] Unlike many types of in situ polymer stabilized VAN cells,
the polymer dopants described here did not decrease the contrast or
optical uniformity of the cells (FIG. 3). Relative to a control
cell prepared with pure VA (FIG. 3, left), the doped-VA cell (FIG.
3, right) shows equally good dark states (top). The bright state
(FIG. 3, bottom) shows significantly better characteristics in the
doped-VA cell. The brightness of the doped-VA cell is appreciably
greater (92 vs. 85 Cd/m.sup.2) than the pure VA cell. More
strikingly, the dependence on viewing angle is much more symmetric
for the doped-VA cell: out to viewing angles of 25.degree. there is
negligible reduction of intensity in any azimuthal direction (in
contrast to the pure VA cell, which shows significant roll-off at
as little as 5.degree. off axis viewing, depending on the azimuthal
orientation of the cell). The degree of improvement is quite
remarkable for such a small amount of dopant. FIG. 16 shows
additional data in a different cell.
[0158] Furthermore, the dopant improves viewing angle, brightness
and contrast without significantly altering the threshold voltage
or saturation voltage. The conoscopic figures of the bright states
of both the pure VA and the doped-VA cells change very little upon
further increase of the imposed voltage to 8V and 10V. Therefore 6V
is very close to the saturation voltage in both cases. Similarly,
note that the threshold voltage is greater than 2V (FIG. 3, second
row is very similar to the dark state above it) and less than 4V
(FIG. 3, third row is similar to the bright state below it) for
both the pure VA and the doped-VA.
D. Elastic and Viscous Constants
[0159] Three concentrations of polymer dopant in negative delta E
nematic hosts were evaluated for their effect on dielectric
anisotropy and their elastic constants. The concentrations tested
were: 0% (no dopant), 0.25%, and 0.5% polymer in the VA nematic
host MLC6608 (Table 6). Quite remarkably, the polymer has no
negative effect on the threshold voltage, and does not
significantly change the dielectric anisotropy (.DELTA..di-elect
cons.) or the elastic constants. In fact, the viscosity is lowered
slightly (by .about.6.5%) at 0.5% weight percent polymer,
indicating that there can be expected an improvement in LC response
from this effect. Considering that addition of polymer often leads
to a significant increase in viscosity and slowing of response,
this result is quite important.
TABLE-US-00007 TABLE 6 Electric Spectroscopy Results for two
concentrations of Polymer 5 in Pure VA host (MLC6608). The addition
of polymer does not appear to detrimentally change any of these
important properties. Properties Pure VA 0.25% Polymer 5 0.50%
Polymer 5 V.sub.th (V) 2.40 2.40 2.40 .DELTA..epsilon. -3.47 -3.51
-3.53 K.sub.11 (pN) 18.1 18.1 18.2 K.sub.33 (pN) 29.3 28.8 28.6
Viscosity (mPas) 223 226 209
[0160] Table 7 shows property data for dopants LCV20141, LCV20117,
and LCV20137 in MLC6886. The data indicates that for the negative
delta E dopant 20141, 0.5 wt % has a lowering effect on viscosity
and other parameters.
TABLE-US-00008 TABLE 7 LC # dopant % conc. Vth Eperp Epara Delta E
K11 K33 K33/K11 Y MLC6886 -- 0 2.4 3.6 6.51 2.91 15.1 21.4 1.42 143
MX40033 20141 0.5 2.2 3.26 5.54 2.29 9.9 24.8 2.49 106 MX40034
20141 0.25 2.4 3.58 6.33 2.75 14.4 21.3 1.48 129 MX40035 20117 0.5
2.4 3.59 6.23 2.65 13.8 22.8 1.65 120 MX40036 20117 0.25 2.5 3.58
6.28 2.70 15.0 20.4 1.36 125 MX40039 20137 0.5 2.4 3.31 6.10 2.80
14.5 29.8 2.06 146 MX40040 20137 0.25 2.6 3.54 6.64 3.11 18.7 24.6
1.32 152
The other dopants (LCV20117, and LCV20137) are positive delta E
phenylpyrimidine dopants.
E. Voltage-Transmission Curves
[0161] FIG. 4 shows the voltage-transmission curve for 0.25 wt %
LCV20137 (Polymer 5 in Scheme 2) in an unrubbed cell in commercial
LC MLC6886. The voltage was held at 6V, 8V or 12V at 80.degree. C.
for 2 minutes, then cooled at 5.degree. C./min, and the
transmittance vs. voltage was recorded as the samples cooled. The
V.sub.th for pure VA (no dopant), 6V, 8V and 12V annealing was all
2 V, indicating the addition of polymer does not increase the
threshold voltage of the LC.
[0162] FIG. 5 shows the voltage-transmission curve for 0.25 wt % of
LCV 20137 and 0.25 wt % LCV20141 (Polymer 6 in Scheme 2) tested in
unrubbed cells using the same procedure as above. The addition of
LC polymer did not increase the threshold voltage of the LC.
Addition of LCV20141 increases the transmittance slightly beyond
that of the pure LC, only after slow annealing 5.degree.
C./min.
[0163] FIG. 6 shows the voltage-transmission curve for 0.1 wt %
LCV20162 (Polymer 7 in Table 2) in rubbed and unrubbed cells. The
voltage was held at 12V AC 1000 Hz at 80.degree. C. for 2 minutes,
then cooled at 10.degree. C./min, and the transmittance v. voltage
was recorded as the samples cooled. Addition of the LC polymer does
not increase the threshold voltage of the LC, and in fact, appears
to decrease it in a rubbed cell. In both rubbed and unrubbed cells,
addition of LCV20162 also appears to increase the transmittance
beyond that of the pure LC even using the faster annealing.
[0164] FIG. 7 shows the voltage-transmission curve for 0.1 wt %
LCV20162 and 0.25 wt % LCV 20162 in rubbed cells. The voltage was
held at 12V AC 1000 Hz at 80.degree. C. for 2 minutes, then cooled
at 10.degree. C./min, recording the transmittance v. voltage as the
samples cooled. Addition of the LC polymer at either concentration
does not increase the threshold voltage of the LC. Addition of 0.1
wt % LCV20162 also appears to increase the transmittance beyond the
pure LC, while addition of 0.25 wt % does not.
[0165] FIG. 13 shows the voltage-transmission curve for 0.25 wt %
MLC6886 in a rubbed cell. The procedure was as follows: the voltage
was held at 12V at 80.degree. C. for 2 mins, then cooled at
5.degree. C./min, recording transmittance v. voltage as samples
cool. In the NLC host the transition from I to N was 75.degree. C.
Annealing conditions were 6V, 8V and 12V.
[0166] FIG. 14 shows the voltage-transmission curve for 0.1 wt %
LCV20141 in MLC6886 in a rubbed cell. The procedure was as follows:
the voltage was held at 12V at 80.degree. C. for 2 mins, then
cooled at 5.degree. C./min, recording transmittance v. voltage as
samples cool. Annealing conditions were 6V, 8V and 12V.
[0167] FIG. 15 shows the voltage-transmission curve for 0.1 wt %
and 0.25 wt % LCV20162 in MLC6886 in a rubbed cell. The procedure
was as follows: the voltage was held at 12V at 80.degree. C. for 2
mins, then cooled at 5.degree. C./min, recording transmittance v.
voltage as samples cool. Annealing conditions were 6V, 8V and
12V.
F. Rise Time/Fall Time Measurements
[0168] Rise time measurements were measured for pure VA LC v.
LCV20137 in unrubbed cells. The host was MLC6886. The results are
shown in FIG. 8. Addition of 0.25 wt % of this polymer (LCV20137)
at all annealing conditions measured decreases the rise time. At
12V annealing condition, the rise time decreases by a factor of
4.
[0169] Fall time measurements were also measured for pure VA LC and
VA LC with LCV20137 in unrubbed cells. The host was MLC6886. The
results are shown in FIG. 9. Addition of 0.25 wt % of this polymer
(LCV20137) at all annealing conditions measured results in no
significant increase or decrease of the fall time.
[0170] Rise and fall time were measured for pure VA LC and VA LC
with LCV20141 in unrubbed cells in host MLC6886. These results are
shown in FIG. 10. Addition of 0.25 wt % of this polymer (LCV20141)
at 12V annealing conditions measured results in a reduction in rise
time and a small increase in fall time.
[0171] Rise and fall time were measured for pure VA LC and VA LC
with LCV20141 in rubbed cells in host MLC6886. These results are
shown in FIG. 11. Addition of 0.25 wt % of this polymer (LCV20141)
at 12V annealing conditions measured results in a 45% reduction in
rise time (88 ms to 48 ms) and a 14% reduction in fall time (5.4 ms
to 4.6 ms).
[0172] Table 8 shows the summary of rise and fall times in rubbed
cells.
TABLE-US-00009 Material Rise Time (ms) Fall Time (ms) Host
(MLC6886) 232 8 Rubbed Cell 0.25% LCV20141 130 4.5 Rubbed Cell 0.1%
LCV20162 85.6 10 Rubbed Cell 0.25% LCV20162 144 8 Rubbed Cell
[0173] In rubbed cells the addition of 0.25 wt % or 0.1 wt % of any
of the polymers results in decreased rise time. In some cases there
was also a reduction in fall time, but in most cases fall time
remains the same or does not increase. It is noted that in data
described herein, the rise and fall times for samples may be
different based on differences in how the cell is manufactured,
buff strength, alignment layer thickness and other factors that can
change this sensitive measurement.
Table 9 shows the response time measurements in rubbed cells.
TABLE-US-00010 Annealing LC Voltage Rise time Fall time MLC-6886
(rubbed cell) 12 232 ms 8.0 ms LCV20141 - 0.25 wt % 12 130 ms 4.5
ms (rubbed cell) LCV20162-0.25 wt % 12 144 ms 8.0 ms (rubbed cell)
LCV20162 - 0.1 wt % 12 86 ms 10 ms (rubbed cell)
G. Temperature Degradation
[0174] FIG. 12 shows temperature degradation data for 0.1 wt %
LCV20162 in rubbed and unrubbed cells. The results show that the
material is stable up to 60.degree. C.
H. Copolymers
[0175] The methods, devices and compositions described here can be
used with copolymer polymer backbones. In this embodiment, there
are two or more different repeating units forming the polymer
backbone. As described elsewhere herein, mesogens can also be
present in the polymer backbone with suitable linking groups, as is
apparent to one of ordinary skill in the art. Some structures
herein describe the use of a
##STR00093##
repeating unit. This repeating unit can be used in conjunction with
other repeating units, such as polystyrene or others described
herein and known in the art in the polymer liquid crystals
described here.
[0176] Although applicant does not wish to be bound by theory, one
possible mechanism that explains the advantageous effect for such a
small amount of polymer is adsorption of the polymer(s) onto
surface of the VAN cell. That being the case, it is obvious that
modifying the polymer for good adsorption to the alignment layer on
the surface of the VAN cell, either by end-functionalization or by
using the LCP polymers as one block in a diblock or triblock
tailored/designed copolymer could further enhance the performance
of the VAN host. Polyimide with aliphatic tails (C.sub.8-C.sub.18
tail length), self-assembled monolayers (SAM) of octyldecyl silane,
for example, and even pure glass have been used to promote
homeotropic alignment in VAN cells, so end-groups or end-blocks can
be either hydrophobic (in the case of the first two alignment
conditions) or hydrophilic (in the case of a pure glass as an
alignment layer). The following is a partial list of some of the
useful end-block structures compatible with hydrophobic alignment
layers where the * indicates there is a repeating unit of various
length between the parenthesis. In some examples the * repeating
unit is the same as described for variable "n" in conjunction with
the
##STR00094##
polymer backbone.
##STR00095##
[0177] The following is a partial list of some useful end-block
structures compatible with hydrophilic/polar alignment layers. In
some examples the * repeating unit is the same as described for
variable "n" in conjunction with the
##STR00096##
polymer backbone.
##STR00097##
[0178] As is known in the art, other groups may be used. As will be
apparent to one of ordinary skill in the art, the end-block and
polymer blocks can be synthesized and attached to each other and to
the remaining sections of the polymer liquid crystal using methods
described here and known in the art.
[0179] The following structures in Scheme 13 below are examples of
triblock copolymers synthesized and examined:
##STR00098##
The variable definitions are the same as described elsewhere
herein.
[0180] These triblock structures have LC-phobic polystyrene blocks
and LC-philic mesogens. The triblock structures were tested in
ZLI2806, which is a commercially available negative delta epsilon
nematic liquid crystal. Addition of triblock copolymers lowered the
threshold voltage, as shown in Table 10.
TABLE-US-00011 TABLE 10 Neat 0.5% Side-on 0.5% End-on Quantity
ZLI2806 Triblock Triblock P 5.53E+010 .OMEGA.*cm 1.04E+010
.OMEGA.*cm 5.28E+009 .OMEGA.*cm V.sub.th 2.10VRMS 2.00VRMS 1.90VRMS
.epsilon..sub..parallel. 3.31 3.71 4.43 .epsilon..sub..perp. 7.39
7.58 8.22 .DELTA..epsilon. -4.08 -3.87 -3.79 K.sub.11[Direct] 20.7
pN 13.4 pN 6.19 pN K.sub.22[Est.] 9.69 pN 8.34 pN 7.37 pN
K.sub.33[Calc.] 16.5 pN 13.9 pN 12.2 pN K.sub.33/K.sub.11 0.8 pN
1.04 1.97
[0181] The structure below is an example of a diblock copolymer
that is useful as the liquid crystal polymer in the compositions
described here. As will be appreciated by one of ordinary skill in
the art, other mesogens and spacers can be used, and different
polymer chain lengths for each of the repeating units can be used.
In addition, the structure below can be formed into a triblock by
adding another polystyrene repeating block onto the polybutadiene
group.
##STR00099##
7. VAN Devices
[0182] As is known in the art, the systems described here can be
incorporated in VAN devices using methods described here and known
in the art.
A. Processing Conditions
[0183] Three aspects used in processing VAN devices are examined:
(i) the interplay of applied voltage and cooling rate in governing
performance of polymer-doped VAN; (ii) the mechanism of "imprinting
pretilt" in the presence of polymer dopant; and (iii) optimal
methods for generating a uniform direction of pretilt over a large
area display. The best effects on switching speed were found when
the cell was exposed to an AC voltage of 8V or more during cooling.
For the most part, the results were equally good for the two
cooling rates examined (10.degree. C./min and 5.degree. C./min).
Therefore, it is likely that even faster cooling rates are
compatible with successful processing of polymer doped VAN--with
obvious relevance to commercialization. In addition to the
technological need for rapid display production, the molecular
characteristics of the polymer (e.g., its size, which governs its
rate of reorientation and diffusion) may influence the speed with
which the desired pretilt can be introduced. In turn the effect of
systematically varied molecular attributes and dopant concentration
on the processing behavior will provide valuable information
regarding the mechanism of the observed effects of LCP dopant. It
has been demonstrated that dopant used in combination with rubbed
alignment layers provides uniform pretilt over the small cells
examined. This approach can be applied to larger cells. In
addition, alternatives known in the art can be used (such as
superimposing a small field in the plane of the cell during the
cooling step).
B. Lifetime Measurements
[0184] The lifetime of the PD-VAN system is tested using methods
known in the art, such as by subjecting the fabricated PD-VAN test
cells at elevated temperature. By using accelerated lifetime
measurement testing at elevated temperature, valuable data on the
lifetime and performance of the PD-VAN LCD system can be
determined. In one method, the physical properties (such as
contrast, brightness, viewing angle, rise time and the fall time of
the test cell) are tested at various time intervals, such as every
10 degrees, starting at room temperature, up to the clearing point
of the liquid crystal mixture.
[0185] As known in the art, other experiments can be carried out to
obtain useful information about the stability and performance of
the system. Some of these experiments are described next. The
specific details for carrying out these experiments is well within
the skill of one of ordinary skill in the art. The critical
temperature at which pre-tilt memory in the PD-VAN cell is lost for
each polymer class can be determined, measuring contrast and rise
times at each temperature, from RT to the clearing point, every 5
degrees. Image "Sticking" can be tested by writing a checker board
image, followed by a black image. The temperature, at which the
checkerboard image ghost remains, after switching to the black
image, is defined as the "sticking point temperature." The
durability of polymer-doped VAN cells can be tested under
temperature cycling in an environmental test chamber. The maximum
and minimum storage temperatures for each class of polymer additive
can be determined by examining each test cell for optical defects
after storage at the appropriate temperature for 36 hours. These
experiments are useful to obtain information about the lifetime of
the PD VAN system.
8. Summary
[0186] It was found that VAN electro-optic properties are improved
using the following general classes of LC polymer dopants: (i) LC
polymers with phenylpyrimidine-based side groups (Scheme 14, left)
that have a small, though still positive dielectric anisotropy
(.DELTA..di-elect cons..apprxeq.+1 or +2), and (ii) LC polymers
with 2,3-difluorophenyl-bicyclohexyl-based side groups (Scheme 14,
right) that have a negative dielectric anisotropy (.DELTA..di-elect
cons..apprxeq.-4). The bicyclohexyl-2,3-difluorophenyl alkoxy unit
was chosen because small molecule LCs with very similar structures
(Scheme 2) perform well in the high resistivity, negative delta E
NLCs used in high-end LCD HDTVs.
##STR00100##
[0187] This research yielded important results that surpassed
expectations. It was first demonstrated that LCPs, by choice of
their mesogen, were easily soluble in negative delta E hosts. Then,
using these polymer-doped VA solutions, it was discovered that
addition of a small amount of LCP dopant, on the order of 0.25%,
into the VA LC host can simultaneously confer three benefits:
reduce the switching speed, increase the contrast and improve
viewing-angle symmetry--without adversely affecting the threshold
voltage, saturation voltage, or viscosity. Indeed, the optical rise
times of the virgin (no dopant) VA nematic LC and its counterpart
doped with 0.25% of Polymer (2) from Scheme 14 show that the rise
time is improved dramatically, from 232 ms to 130 ms, by addition
of the polymer dopant (see data). The fall time is also improved,
from 8.0 ms to 4.5 ms (see data). LC Polymer (1) in Scheme 14 gave
qualitatively similar improvements, but not as large as those
observed for (2) in Scheme 14; therefore, pendant mesogens with
negative dielectric anisotropy (like their VA nematic host) appear
more promising for VAN dopant technology.
[0188] Although applicant does not wish to be bound by theory, the
results provided here (including some results that are not shown)
indicate that in general there is not a great deal of fall time
differences between rubbed/un rubbed conditions. The fall times are
all under 8.about.10 ms. The rubbed and un-rubbed cells did show
large differences in the rise time. The rise times are almost
1000.times. different between rubbed and un-rubbed cells. These
results show the advantages of a rubbed cell in orientation,
pre-tilt angle, and surface anchoring energy. An advantage in any
of the properties from the liquid crystal polymers described here
is useful. The rubbed (also known as buffed) cell has advantages in
all three properties. Some of the liquid crystal polymers provide
an enhancement in the orientation and pre-tilt angle, making the
doped polymer systems even faster in the rise time comparing to the
pure VA cell without liquid crystal polymer. In addition, the
contrast ratio of compositions including liquid crystal polymer is
improved as compared to systems that do not contain liquid crystal
polymer.
[0189] It should be noted that for the above test, a simple 1 KHz
5V AC drive signal was used; in real VA displays, many other
techniques (e.g., overdrive schemes coupled with lookup tables),
are used to achieve more rapid rise time, so the present rise times
would yield much faster response in practice.
[0190] This dramatic decrease in rise time suggests that the LC
polymers do, indeed, increase the pretilt of the LCs, while the
decrease in the fall time suggests that the LC polymer is also
providing an anchoring condition that induces the molecules to
relax back faster.
[0191] An exciting discovery was made while comparing LCP
homopolymers to coil-LCP-coil block copolymers. Although small
concentrations of dissolved LCPs in a nematic LC are not expected
to change the strength or direction of anchoring at the
"orientation layer" (FIG. 1), it was discovered that the
application of a moderate AC voltage (12V at 1 kHz) for a few
minutes to a cell filled with LC polymer doped VAN during cooling
from the isotropic to the nematic phase introduces a highly
desirable pretilt relative to the z-axis, manifested by a
substantial reduction of the rise time (the time for the
transmitted intensity to reach 90% of the "bright state" value). In
the absence of pretilt (FIG. 1, bottom left), the resting state of
the cell (field off) affords very little coupling between the
dipole of the LC and the applied field (molecules perfectly aligned
along z experience no torque and the direction of the torque
averages to zero, since there are as many molecules experiencing a
torque to the left as to the right, for example). Even a small
pretilt (compatible with very good extinction in the dark state) is
sufficient to break symmetry, so there is a net torque acting on
the director as soon as the field is applied (FIG. 1, bottom
right). In addition, the field-treated polymer doped-LC decreases
the fall time (the time for the transmitted intensity to relaxing
back to 90% of the dark state), indicating that the strength of
anchoring is increased by the polymer. These effects are not
present in the LC alone, and occur even at very low LCP
concentrations (for example 0.25 wt % as shown here)
[0192] The results described herein show that a small amount of LC
polymer additive is useful for improving contrast and brightness,
while reducing the rise time. The sign of the dielectric anisotropy
of the mesogenic side groups affects the results: LC polymers
bearing mesogens that have .DELTA..di-elect cons.>0 are good and
mesogens that have .DELTA..di-elect cons.<0 are even better by
all three display performance criteria--contrast, brightness, and
rise time. Low concentrations perform very well, indicating that
further dilution of the dopant in the VA host may improve
performance further. The magnitude of the AC voltage applied while
the cell is cooled through the isotropic-nematic transition is an
important variable, with excellent performance being achieved with
readily-accessible voltages (8-10V) under conditions that require
only a few minutes.
[0193] LC Polymers are poised for rapid, widespread adoption in the
VAN display industry. They provide a "drop in solution" for
introducing a small pretilt that confers fast response without
causing light leakage. The complex infrastructure for UV
irradiation is not needed at all. The electrodes that are already
part of the LCD can be used to apply the "annealing voltage" during
the cooling step after filling the cell. The polymer dopant
approach eliminates formation of the undesired by-products of UV
irradiation (ions and radicals that increase power consumption and
reduce the lifetime of a display). Furthermore, polymer dopants
expand the range of small molecules that can incorporated in VAN
mixtures to optimize their properties. Of special importance are
components in nematic liquid crystal hosts that contain unsaturated
bonds in their "tails." This structural motif is known to improve
response time--the central unmet demand in VAN LCDs; however,
unsaturated groups are destroyed by strong UV irradiation. The
current process allows the use of alkenes in hosts, giving access
to a greater range of viscosity lowering LC components to afford a
lower viscosity and thus faster switching VA NLC mixture.
Therefore, polymer dopants open the way to new VAN mixtures with
lower viscosity (hence, faster rise time). Polymer dopants improve
the quality of VAN displays in key areas, including speed, contrast
and lifetime. At the same time, doped VA nematics will reduce
production costs and bottlenecks associated with UV irradiation
processing lines.
STATEMENTS REGARDING INCORPORATION BY REFERENCE AND VARIATIONS
[0194] All references throughout this application, for example
patent documents including issued or granted patents or
equivalents; patent application publications; and non-patent
literature documents or other source material; are hereby
incorporated by reference herein in their entireties, as though
individually incorporated by reference, to the extent each
refdrence is at least partially not inconsistent with the
disclosure in this application (for example, a reference that is
partially inconsistent is incorporated by reference except for the
partially inconsistent portion of the reference).
[0195] The terms and expressions which have been employed herein
are used as terms of description and not of limitation, and there
is no intention in the use of such terms and expressions of
excluding any equivalents of the features shown and described or
portions thereof, but it is recognized that various modifications
are possible within the scope of the invention claimed. Thus, it
should be understood that although the invention has been
specifically disclosed by preferred embodiments, exemplary
embodiments and optional features, modification and variation of
the concepts herein disclosed may be resorted to by those skilled
in the art, and that such modifications and variations are
considered to be within the scope of this invention as defined by
the appended claims. The specific embodiments provided herein are
examples of useful embodiments of the invention and it will be
apparent to one skilled in the art that the invention may be
carried out using a large number of variations of the devices,
device components, methods steps set forth in the present
description. As will be obvious to one of skill in the art, methods
and devices useful for the present methods can include a large
number of optional composition and processing elements and
steps.
[0196] When a group of substituents is disclosed herein, it is
understood that all individual members of that group and all
subgroups, including any isomers, enantiomers, and diastereomers of
the group members, are disclosed separately. When a Markush group
or other grouping is used herein, all individual members of the
group and all combinations and subcombinations possible of the
group are intended to be individually included in the disclosure.
When a compound is described herein such that a particular isomer,
enantiomer or diastereomer of the compound is not specified, for
example, in a formula or in a chemical name, that description is
intended to include each isomers and enantiomer of the compound
described individual or in any combination. Additionally, unless
otherwise specified, all isotopic variants of compounds disclosed
herein are intended to be encompassed by the disclosure. For
example, it will be understood that any one or more hydrogens in a
molecule disclosed can be replaced with deuterium or tritium.
Isotopic variants of a molecule are generally useful as standards
in assays for the molecule and in chemical and biological research
related to the molecule or its use. Methods for making such
isotopic variants are known in the art. Specific names of compounds
are intended to be exemplary, as it is known that one of ordinary
skill in the art can name the same compounds differently.
[0197] All possible ionic forms of molecules described herein and
salts thereof are intended to be included individually in the
disclosure herein.
[0198] Every formulation or combination of components described or
exemplified herein can be used to practice the invention, unless
otherwise stated.
[0199] Whenever a range is given in the specification, for example,
a temperature range, a time range, or a composition or
concentration range, all intermediate ranges and subranges, as well
as all individual values included in the ranges given are intended
to be included in the disclosure. It will be understood that any
subranges or individual values in a range or subrange that are
included in the description herein can be excluded from the claims
herein.
[0200] All patents and publications mentioned in the specification
are indicative of the levels of skill of those skilled in the art
to which the invention pertains.
[0201] As used herein, "comprising" is synonymous with "including,"
"containing," or "characterized by," and is inclusive or open-ended
and does not exclude additional, unrecited elements or method
steps. As used herein, "consisting of" excludes any element, step,
or ingredient not specified in the claim element. As used herein,
"consisting essentially of" does not exclude materials or steps
that do not materially affect the basic and novel characteristics
of the claim. In each instance herein any of the terms
"comprising", "consisting essentially of" and "consisting of" may
be replaced with either of the other two terms. The invention
illustratively described herein suitably may be practiced in the
absence of any element or elements, limitation or limitations which
is not specifically disclosed herein.
[0202] One of ordinary skill in the art will appreciate that
starting materials, reagents, synthetic methods, purification
methods, analytical methods, assay methods, and devices other than
those specifically exemplified can be employed in the practice of
the invention without resort to undue experimentation. All
art-known functional equivalents, of any such materials and methods
are intended to be included in this invention. The terms and
expressions which have been employed are used as terms of
description and not of limitation, and there is no intention in the
use of such terms and expressions of excluding any equivalents of
the features shown and described or portions thereof, but it is
recognized that various modifications are possible within the scope
of the invention claimed. Thus, it should be understood that
although the invention has been specifically disclosed by preferred
embodiments and optional features, modification and variation of
the concepts herein disclosed may be resorted to by those skilled
in the art, and that such modifications and variations are
considered to be within the scope of this invention as defined by
the appended claims. Any composition or compound that is claimed
and that is described in the literature with an enabling disclosure
is not intended to be included in the claims and it is intended
that specific support is provided to exclude a compound or class of
compounds from the claims.
[0203] The disclosures of the publications listed herein including
the publications listed below are herein incorporated by reference
in their entireties.
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