U.S. patent application number 16/607382 was filed with the patent office on 2020-04-30 for high-strength low-creep thermoplastic elastomer.
This patent application is currently assigned to THE UNIVERSITY OF AKRON. The applicant listed for this patent is Joseph NUGAY KENNEDY. Invention is credited to Joseph KENNEDY, Nihan NUGAY, Turgut NUGAY.
Application Number | 20200131294 16/607382 |
Document ID | / |
Family ID | 65015332 |
Filed Date | 2020-04-30 |
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United States Patent
Application |
20200131294 |
Kind Code |
A1 |
KENNEDY; Joseph ; et
al. |
April 30, 2020 |
HIGH-STRENGTH LOW-CREEP THERMOPLASTIC ELASTOMER
Abstract
A polystyrene-g-(polyisobutylene-b-polystyrene) is taught. The
polystyrene-g-(polyisobutylene-b-polystyrene) is synthesized by
first providing a polystyrene backbone. Once the polystyrene
backbone is provided, the polystyrene backbone is acetylated to
provide acetyl groups on the polystyrene backbone. Next, the acetyl
groups are converted to --C(CH.sub.3).sub.2OH groups. Finally, the
living polymerization of isobutylene is initiated, which is then
followed by the living block polymerization of styrene. A polymer
network of polystyrene-g-(polyisobutylene-b-polystyrene)s is also
provided.
Inventors: |
KENNEDY; Joseph; (Akron,
OH) ; NUGAY; Turgut; (Sariyer-Istanbul, TR) ;
NUGAY; Nihan; (Sariyer-Istanbul, TR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KENNEDY; Joseph
NUGAY; Turgut
NUGAY; Nihan |
Akron
Sariyer-Istanbul
Sariyer-Istanbul |
OH |
US
TR
TR |
|
|
Assignee: |
THE UNIVERSITY OF AKRON
AKRON
OH
|
Family ID: |
65015332 |
Appl. No.: |
16/607382 |
Filed: |
July 18, 2018 |
PCT Filed: |
July 18, 2018 |
PCT NO: |
PCT/US18/42636 |
371 Date: |
October 23, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62533706 |
Jul 18, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 285/00 20130101;
C08F 8/02 20130101; C08F 297/00 20130101; C08F 10/08 20130101; C08F
8/20 20130101; C08F 8/10 20130101; C08F 8/04 20130101; C08F 257/02
20130101; C08F 12/08 20130101; C08F 2438/00 20130101; C08F 8/02
20130101; C08F 8/04 20130101; C08F 8/10 20130101; C08F 112/08
20130101; C08F 8/10 20130101; C08F 112/08 20130101; C08F 257/02
20130101; C08F 210/10 20130101; C08F 257/02 20130101; C08F 212/08
20130101; C08F 8/20 20130101; C08F 8/02 20130101; C08F 8/04
20130101; C08F 8/10 20130101; C08F 112/08 20130101; C08F 8/02
20130101; C08F 8/02 20130101; C08F 8/04 20130101; C08F 8/10
20130101; C08F 112/08 20130101 |
International
Class: |
C08F 257/02 20060101
C08F257/02; C08F 285/00 20060101 C08F285/00; C08F 12/08 20060101
C08F012/08; C08F 10/08 20060101 C08F010/08; C08F 8/10 20060101
C08F008/10; C08F 8/20 20060101 C08F008/20 |
Claims
1. A polystyrene-g-(polyisobutylene-b-polystyrene).
2. The polystyrene-g-(polyisobutylene-b-polystyrene) of claim 1
having a tensile strength of greater than 20 MPa.
3. The polystyrene-g-(polyisobutylene-b-polystyrene) of claim 1
having an elongation of greater than 400%.
4. A method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) comprising the steps
of: providing a polystyrene backbone; acetylating the polystyrene
backbone to provide between about 2 and about 20 acetyl groups on
the polystyrene backbone; converting the acetyl groups to
--C(CH3)2OH groups; and initiating in the presence of a
co-initiator the living block polymerizations of isobutylene
followed by styrene.
5. The method of claim 4, wherein the step of acetylating provides
between 4 and 7 acetyl groups on the polystyrene backbone.
6. The method of claim 4, wherein the step of acetylating provides
5 or 6 acetyl groups on the polystyrene backbone.
7. The method of claim 4, wherein prior to the step of initiating,
the --C(CH3)2OH groups are converted to --C(CH3)2Cl groups.
8. The method of claim 7, wherein the step of converting the
--C(CH3)2OH groups to --C(CH3)2Cl groups uses hydrogen chloride to
convert the --C(CH3)2OH groups to --C(CH3)2Cl groups.
9. The method of claim 4, wherein prior to the step of initiating,
the --C(CH3)2OH groups are converted to --C(CH3)2OMe groups.
10. The method of claim 9, wherein the step of converting the
--C(CH3)2OH groups to --C(CH3)2OMe groups uses sodium hydride and
methyl iodide to convert the --C(CH3)2OH groups to --C(CH3)2OMe
groups.
11. The method of claim 4, wherein the co-initiator is TiCl4.
12. The method of claim 11, wherein the polymerization is
terminated by methanol so as to precipitate the
polystyrene-g-(polyisobutylene-b-polystyrene) and to decompose the
TiCl4.
13. The method of claim 4, wherein the molecular weight of the
polystyrene backbone is from about 5,000 g/mol to about 50,000
g/mol.
14. The method of claim 4, wherein the method produces a
polystyrene-g-(polyisobutylene-b-polystyrene) having multiple
polyisobutylene branch segments, and wherein the molecular weight
of each of the multiple polyisobutylene branch segments is from
about 10,000 g/mol to about 60,000 g/mol.
15. The method of claim 4, wherein the method produces a
polystyrene-g-(polyisobutylene-b-polystyrene) having multiple
polystyrene branch segments, and wherein the molecular weight of
each of the multiple polystyrene branch segments is from about
5,000 g/mol to about 50,000 g/mol.
16. The method of claim 4, wherein the step of acetylating uses
acetyl chloride in the presence of aluminum chloride, and wherein
methylene chloride is a solvent to provide para-acetyl groups on
the polystyrene backbone.
17. The method of claim 16, wherein the step of converting the
acetylated groups first uses methyl magnesium bromide, and then
water or tetrahydrofuran to convert the acetylated groups to
--C(CH3)2OH groups.
18. The method of claim 4 wherein the
polystyrene-g-(polyisobutylene-b-polystyrene) synthesized has a
tensile strength of greater than 20 MPa.
19. The method of claim 4 wherein the
polystyrene-g-(polyisobutylene-b-polystyrene) synthesized has an
elongation of greater than 400%.
20. A polymer network of
polystyrene-g-(polyisobutylene-b-polystyrene).
21. The polymer network of claim 20 wherein each
polystyrene-g-(polyisobutylene-b-polystyrene) in the network
contains a polystyrene backbone, multiple polystyrene branch
segments, and multiple polyisobutylene branch segments.
22. The polymer network of claim 21 wherein each polystyrene branch
segment of polystyrene-g-(polyisobutylene-b-polystyrene) in the
network aggregate towards other polystyrene branch segments of
other polystyrene-g-(polyisobutylene-b-polystyrene)s.
23. The network of claim 22 wherein the polyisobutylene branch
segments of each polystyrene-g-(polyisobutylene-b-polystyrene) in
the network prevent aggregation of the polystyrene backbones of
each polystyrene-g-(polyisobutylene-b-polystyrene).
24. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 62/533,706 entitled "Graft SIBS: A New
High-Strength Low-Creep Thermoplastic Elastomer" filed Jul. 18,
2017, which is incorporated herein by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a novel thermoplastic
elastomer. More particularly, the present invention relates to a
novel thermoplastic elastomer exhibiting advantageous mechanical
properties such as high strength and very low creep. Specifically,
the present invention relates to the structure and synthesis of a
polystyrene-g-(polyisobutylene-b-polystyrene) (PSt-g-P(IB-b-St)),
wherein the living cationic polymerization of isobutylene may be
initiated by various one or more functionalized polystyrene
backbones at various sites along the at least one polystyrene
backbone. The resulting structure provides for two or more
polyisobutylenes grafted to any one polystyrene backbone, wherein
styrene can then be polymerized after the isobutylene, so as to
provide a PSt-g-P(IB-b-St) as defined herein exhibiting
advantageous mechanical properties such as, amongst others,
high-strength and very low creep. The present invention also
relates to polymer networks of PSt-g-P(IB-b-St).
BACKGROUND OF THE INVENTION
[0003] Poly(Styrene-b-Isobutylene-b-Styrene) (SIBS) is a
thermoplastic elastomer that has gained attention recently due to
its high degree of biocompatibility. Due to its biocompatibility,
SIBS has been found to be useful for a variety of application, such
as stent coating, stoppers, glaucoma shunt, and tubing. This linear
block copolymer has a triblock structure formed by a
polyisobutylene (PIS) core sandwiched between blocks of polystyrene
(PS). The formulation of SIBS can be tailored for different
applications by changing the weight percentage of PS or by changing
the molecular weight of the polymer chains. The hard PS blocks
provide SIBS with a glassy microstructure that enhances mechanical
strength and rigidity of the material, while the PIS has a soft
microstructure with increased chain mobility that gives the polymer
its elastomeric properties. The possibility of tailoring mechanical
properties, together with the high degree of biocompatibility,
makes SIBS an ideal material for use in biomedical devices.
[0004] However, there is a high cost associated with making SIBS.
The high cost (30-40%) of most SIBS products is largely due to the
expensive bifunctional polymerization initiator need for synthesis.
Typically, that expensive bifunctional polymerization initiator is
1-(tert-butyl)-3,5-bis(2-chloropropan-2-yl)benzene. A commercial
version of SIBS, named SIBSTAR, available from Kaneka Co., used
mainly as additive in various industrial applications, is strongly
contaminated with ill-defined diblocks.
[0005] Block copolymers of similar compositions might have diverse
mechanical properties due to their composite nature. Parameters
such as molecular weight, block weight percentage, and polymer
chain structure are known to give rise to different microstructures
that in turn lead to different material properties. Different
grades of SIBS can have very different morphologies based on the
ratio of hard phase to soft phase. At lower contents of PS, the
hard phase forms spherical domains through the soft matrix. As the
PS content increases, the spherical domains become double gyroid
structures, and as the PS content is further increased, the
structure of the hard phase becomes lamellar. It is likely that the
incompatibility of the soft and hard phases leads to micro-phase
separations and results in the different morphologies described. It
is well known that for composite systems, the interface between
different phases plays a major role in the performance of the
material. A weakened interface might lead to premature cracking and
failure. Additionally, the method of fabrication for SIBS might
play a very important role due to the incompatibility of the
different phases. Therefore, different methods may result in
different qualities of the interface.
[0006] However, for all of its attributes, SIBS has been found to
be of modest strength and tends to exhibit high creep. Therefore,
the need exists for a new material, useful for implantable medical
devices and industrial applications, that has the key advantageous
properties of SIBS, such as biocompatibility, biostability,
elasticity, and processability, but that also exhibits higher
strength, toughness, and diminished creep, which SIBS does not
exhibit. Furthermore, this new material should be able to be
synthesized without the use of a costly multi-functional
initiator.
SUMMARY OF THE INVENTION
[0007] In one embodiment, the present invention provides a
polystyrene-g-(polyisobutylene-b-polystyrene). Said another way,
the present invention provides a polymer composition having a
polystyrene backbone and at least two polyisobutylene-polystyrene
block copolymers grafted to the polystyrene backbone.
[0008] In another embodiment, the present invention provides the
polystyrene-g-(polyisobutylene-b-polystyrene) in the embodiment
above, wherein the graft-block copolymer has a tensile strength of
greater than 20 MPa.
[0009] In another embodiment, the present invention provides a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the graft-block copolymer has an elongation of
greater than 400%.
[0010] In a further embodiment, the present invention provides a
method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) comprising the steps
of providing a polystyrene backbone; acetylating the polystyrene
backbone to provide between about 2 and about 20 acetyl groups on
the polystyrene backbone; converting the acetyl groups to
--C(CH.sub.3).sub.2OH groups; and initiating in the presence of a
co-initiator the living block polymerizations of isobutylene
followed by styrene. More particularly, the living block
polymerizations may be the living cationic polymerization of
isobutylene followed by the living cationic polymerization of
stryene.
[0011] In a related embodiment, the present invention provides a
method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the step of acetylating provides between 3 and 7
acetyl groups and preferably 4 and 7 acetyl groups, on the
polystyrene backbone.
[0012] In another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the step of acetylating provides 5 or 6 acetyl
groups on the polystyrene backbone.
[0013] In yet another embodiment, the present invention provides a
method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein prior to the step of initiating, the
--C(CH.sub.3).sub.2OH groups are converted to --C(CH.sub.3).sub.2Cl
groups.
[0014] In another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the step of converting the --C(CH.sub.3).sub.2OH
groups to --C(CH.sub.3).sub.2Cl groups uses hydrogen chloride to
convert the --C(CH.sub.3).sub.2OH groups to --C(CH.sub.3).sub.2Cl
groups.
[0015] In still another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein prior to the step of initiating, the
--C(CH.sub.3).sub.2OH groups are converted to
--C(CH.sub.3).sub.2OMe groups.
[0016] In yet another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the step of converting the --C(CH.sub.3).sub.2OH
groups to --C(CH.sub.3).sub.2OMe groups uses sodium hydride and
methyl iodide to convert the --C(CH.sub.3).sub.2OH groups to
--C(CH.sub.3).sub.2OMe groups.
[0017] In another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the co-initiator is TiCl.sub.4.
[0018] In a further related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the polymerization is terminated by methanol so as
to precipitate the polystyrene-g-(polyisobutylene-b-polystyrene)
and to decompose the TiCl.sub.4.
[0019] In a further embodiment, the present invention provides a
method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the molecular weight of the polystyrene backbone is
from about 5,000 g/mol to about 50,000 g/mol.
[0020] In still another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the method produces a
polystyrene-g-(polyisobutylene-b-polystyrene) having multiple
polyisobutylene branch segments, and wherein the molecular weight
of each of the multiple polyisobutylene branch segments is from
about 10,000 g/mol to about 60,000 g/mol.
[0021] In another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the method produces a
polystyrene-g-(polyisobutylene-b-polystyrene) having multiple
polystyrene branch segments, and wherein the molecular weight of
each of the multiple polystyrene branch segments is from about
5,000 g/mol to about 50,000 g/mol.
[0022] In another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the step of acetylating uses acetyl chloride in the
presence of aluminum chloride, and wherein methylene chloride is a
solvent to provide para-acetyl groups on the polystyrene
backbone.
[0023] In yet another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the step of converting the acetylated groups first
uses methyl magnesium bromide, and then water or tetrahydrofuran to
convert the acetylated groups to --C(CH.sub.3).sub.2OH groups.
[0024] In still another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the polystyrene-g-(polyisobutylene-b-polystyrene)
synthesized has a tensile strength of greater than 20 MPa.
[0025] In yet another related embodiment, the present invention
provides a method of synthesizing a
polystyrene-g-(polyisobutylene-b-polystyrene) as in any embodiment
above, wherein the polystyrene-g-(polyisobutylene-b-polystyrene)
synthesized has an elongation of greater than 400%.
[0026] In another embodiment, the present invention provides a
polymer network of
polystyrene-g-(polyisobutylene-b-polystyrene).
[0027] In a further related embodiment, the present invention
provides a polymer network as in any embodiment above, wherein each
polystyrene-g-(polyisobutylene-b-polystyrene) in the polymer
network contains a polystyrene backbone, multiple polystyrene
branch segments, and multiple polyisobutylene branch segments.
[0028] In yet a further related embodiment, the present invention
provides a polymer network as in any embodiment above, wherein each
polystyrene branch segment of each
polystyrene-g-(polyisobutylene-b-polystyrene) in the network
aggregate towards other polystyrene branch segments of other
polystyrene-g-(polyisobutylene-b-polystyrene) s.
[0029] In still a further related embodiment, the present invention
provides a polymer network as in any embodiment above, wherein the
polyisobutylene branch segments of each
polystyrene-g-(polyisobutylene-b-polystyrene) in the network
prevent aggregation of the polystyrene backbones of each
polystyrene-g-(polyisobutylene-b-polystyrene).
[0030] In a further embodiment, the present invention provides an
initiator for the polymerization of isobutylene, wherein the
initiator is a functionalized polystyrene wherein the
functionalized polystyrene has reactive groups selected from the
group consisting of --OH, --Cl, or --OMe groups functionalized and
extending from at least two benzene rings of the polystyrene
backbone. More particularly, the reactive groups extend from the
para position on the benzene rings. In another embodiment, the
reactive groups extend from no more than about 20 benzene rings of
the polystyrene backbone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] For a more complete understanding of the features and
advantages of the present invention, reference is now made to the
detailed description of the invention along with the accompanying
figures in which:
[0032] FIG. 1 is a representative structural formula of a
PSt-g-P(IB-b-St); and
[0033] FIG. 2 is a representative microarchitecture of a
representative PSt-g-P(IB-b-St).sub.5 polymer network.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0034] The present invention generally relates to a novel
thermoplastic elastomer having improved mechanical properties over
ordinary thermoplastic elastomers. It will be appreciate that the
generally recognized understanding of the term "thermoplastic
elastomer" refers to the class of copolymers or a physical mix of
polymers (usually a plastic and a rubber) which consist of
materials with both thermoplastic and elastomeric properties.
Thermoplastic elastomers typically show advantages typical of both
rubbery materials and plastic materials.
[0035] The novel thermoplastic elastomer of the present invention
is a polystyrene-g-(polyisobutylene-b-polystyrene)
(PSt-g-P(IB-b-St)). Polystyrene-g-(polyisobutylene-b-polystyrene)
is defined as a polymer composition comprising a polystyrene
backbone and at least two, (and less than about 20 per 5000 g/mol
polystyrene backbone) polyisobutylene-polystyrene block copolymers
grafted to the polystyrene backbone at at least two (and up to
about 20 per 5000 g/mol polystyrene backbone) of the benzene rings
of the polystyrene backbone. The polyisobutylene-b-polystyrene
copolymers are not present at the end of the polystyrene backbone
chain, but rather are grafted within the polystyrene backbone, or
more specifically, are connected two or more of the benzene rings
of the polystyrene backbone. It will be appreciated that two or
more of the benzene ring structures of the polystyrene backbone
have previously been functionalized with a --OH, --Cl or --OMe
group, preferably at the para position on the benzene ring
structures, so as to enable the initiation of living cationic
polymerization of isobutylene, when in the presence of a
co-initiator. Subsequently, styrene can then be polymerized after
the isobutylene, so as to provide the polyisobutylene-polystyrene
block copolymer moiety. The resulting structure provides for two or
more polyisobutylenes (and subsequently, two or more
polyisobutylene-b-polystyrene(s)) grafted to any one polystyrene
backbone.
[0036] It has been found that the novel PSt-g-P(IB-b-St) of the
present invention exhibits advantageous mechanical properties such
as, amongst others, high-strength and very low creep. Inasmuch as
the thermoplastic elastomer itself is novel, the synthesis of the
PSt-g-P(IB-b-St) is also novel in that it produces a thermoplastic
elastomer exhibiting advantageous mechanical properties such as,
amongst others, high-strength and very low creep. An additional
important feature of the synthesis of the PSt-g-P(IB-b-St) is that
the synthesis does not require the use of a costly bifunctional
initiator, such as
1-(tert-butyl)-3,5-bis(2-chloropropan-2-yl)benzene. Instead, the
synthesis of the PSt-g-P(IB-b-St) utilizes a functionalized
polystyrene having either an --OH, --Cl, or --OMe group extending
from at least two of the benzene rings of the functionalized
polystyrene.
[0037] When the term "high-strength" is used in the context of the
present invention, it can be defined as a material having a tensile
strength of greater than 20 MPa, or, an elongation, as defined on a
stress-strain curve, of greater than 400%, and more preferably,
greater than 600% strain, as determined by ASTM D638--Plastic
Tensile Strength Test. It will be appreciated that SIBS does not
have such a high tensile strength or elongation, in that SIBS is
well known to have tensile strength below 20 MPa, and elongation
less than 400% as determined by the same ASTM standards.
[0038] When the term "very low creep" is used in the context of the
present invention, it can be defined as a material having less than
0.2% creep as determined by ASTM D2990-77--Standard Test Method for
Tensile, Compressive and Flexural Creep and Creep Rupture of
Plastics. It will be appreciated that SIBS is well known to have
poor creep properties, in that SIBS is well known to have creep
well above at least 0.5%, and higher as determined by the same ASTM
standard.
[0039] As stated above, the synthesis of the PSt-g-P(IB-b-St) of
the present invention does not require the use of an expensive
initiator to initiate, or start, polymerization. Instead, the
present invention utilizes a functionalized polystyrene as the
initiator for the polymerization of isobutylene. In one or more
embodiments of the present invention, the functionalized
polystyrene used as the initiator for the polymerization of
isobutylene contains --OH, --Cl, or --OMe terminal groups. In one
or more embodiments of the present invention, the initiation takes
place in the presence of a co-initiator. As defined within the
context of the present invention, a co-initiator differs from a
typical initiator in that a co-initiator will get eliminated, or
washed away, from the final product and will leave behind no
residue. The use of a functionalized polystyrene as an initiator
and the use of a co-initiator in the synthesis of the present
invention is an important feature in producing PSt-g-P(IB-b-St)
because it improves the overall processability of the
PSt-g-P(IB-b-St) as compared to the processability of SIBS., and at
a much lower cost. In at least one embodiment, the polymerization
that is initiated is the living cationic polymerization of the
isobutylene followed by the living cationic polymerization of
styrene.
[0040] In one embodiment of the present invention, the following
synthesis route is taken to arrive at the novel thermoplastic
elastomer, PSt-g-P(IB-b-St), of the present invention. To begin, a
polystyrene backbone is provided. Then, the polystyrene backbone is
acetylated so as to provide acetyl groups on the polystyrene
backbone. Once the acetyl groups are provided on the polystyrene
backbone, the acetyl groups are then converted to
--C(CH.sub.3).sub.2OH groups. Finally, living block polymerization
of isobutylene followed by styrene is initiated utilizing a
functionalized polystyrene in the presence of a co-initiator to
create the novel thermoplastic elastomer PSt-g-P(IB-b-St) of the
present invention.
[0041] In one embodiment of the present invention, the polystyrene
backbone is acetylated by the use of acetyl chloride in the
presence of aluminum chloride, and wherein methylene chloride is
used as a solvent so as to provide acetyl groups on the polystyrene
backbone. In one or more embodiments, the acetyl groups provided on
the polystyrene backbone are para-acetyl groups.
[0042] In one embodiment of the present invention, the step of
converting the acetyl groups first uses methyl magnesium bromide,
and then water to convert the acetyl groups to
--C(CH.sub.3).sub.2OH groups. In another embodiment, the step of
converting the acetyl groups first uses methyl magnesium bromide,
and then tetrahydrofuran to convert the acetyl groups to
--C(CH.sub.3).sub.2OH groups.
[0043] In one embodiment of the present invention, after the step
of converting the acetyl groups to --C(CH.sub.3).sub.2OH groups,
the --C(CH.sub.3).sub.2OH groups are then converted to
--C(CH.sub.3).sub.2Cl groups using hydrogen chloride to convert the
--C(CH.sub.3).sub.2OH groups to --C(CH.sub.3).sub.2Cl groups. In
yet another embodiment of the present invention, after the step of
converting the acetyl groups to --C(CH.sub.3).sub.2OH groups, the
--C(CH.sub.3).sub.2OH groups are then converted to
--C(CH.sub.3).sub.2OMe groups using sodium hydride and methyl
iodide to convert the --C(CH.sub.3).sub.2OH groups to
--C(CH.sub.3).sub.2OMe groups.
[0044] In one or more embodiments of the present invention,
regardless of whether the acetyl groups have been converted to
--C(CH.sub.3).sub.2OH groups, --C(CH.sub.3).sub.2Cl groups, or
--C(CH.sub.3).sub.2OMe groups, the living block polymerization is
initiated using the functionalized polystyrene and is coinitiated
using titanium chloride and the polymerization is terminated by
methanol so as to precipitate the novel thermoplastic elastomer
PSt-g-P(IB-b-St) of the present invention and to decompose the
remaining titanium chloride co-initiator.
[0045] FIG. 1 shows the structural formula of the novel
thermoplastic elastomer PSt-g-P(IB-b-St) of one or more embodiments
of the present invention. In one or more embodiments, the molecular
weight of the polystyrene backbone of the novel thermoplastic
elastomer is from about 5,000 g/mol to about 50,000 g/mol; the
molecular weight of the polyisobutylene branches of the novel
thermoplastic elastomer are from about 10,000 g/mol to about 60,000
g/mol; and the molecular weight of the polystyrene branches are
from about 5,000 g/mol to about 50,000 g/mol. In one embodiment,
the molecular weight of the polystyrene backbone of the novel
thermoplastic elastomer is about 13,000 g/mol; the molecular weight
of the polyisobutylene branches of the novel thermoplastic
elastomer are about 30,000 g/mol; and the molecular weight of the
polystyrene branches are about 13,000 g/mol.
[0046] The molecular weights and their distribution of both the
polystyrene and polyisobutylene segments can be precisely
controlled by living cationic polymerization. In one or more
embodiments of the present invention, it is believed that the
superior combination of thermoplastic properties is obtained with a
hard (polystyrene)/soft (polyisobutylene) segment ratio of from
about 30/70 wt. % to about 40/60 wt. %. For example, with a
targeted 30/70 wt. % hard/soft segment ratio, the molecular weight
of the polystyrene segment should be between about 13,000 and
14,000 g/mol so as to obtain the maximum Tg (.about.100.degree. C.)
for the hard segment, and the molecular weight of the soft
polyisobutylene segments should be about 30,000 g/mol. The
morphology with either 30/70 wt. % hard/soft segment, or 40/60 wt.
% hard/soft segment is expected to be spherical.
[0047] In one or more embodiments of the present invention, the
molecular weights of both the polystyrene backbone and the
polystyrene branch segments should be the same. The similarity in
molecular weights is believed to give the desirable micromorphology
of the elastomer of the present invention.
[0048] FIG. 2 shows the unique microarchitecture of a polymer
network of PSt-g-P(IB-b-St) of the present invention. Each
PSt-g-P(IB-b-St) of the network contains a rigid glassy segment
carrying several rubbery-glassy segments. More particularly, each
PSt-g-P(IB-b-St) in the polymer network contains a polystyrene
backbone, multiple polystyrene branches, and multiple
polyisobutylene branches.
[0049] The polyisobutylene branches largely prevent the aggregation
of polystyrene backbones so that physical crosslinking will mainly
involve unencumbered polystyrene branch segments. The physical
crosslinking, or aggregation thereof, of the polystyrene branch
segments is believed to take place due to van der Waals forces
between the polystyrene branch segments. This microarchitecture,
also commonly known as a polymer network, constrains extensibility
but leads to multiple entanglements and better stress distribution,
which result in superior strength and the virtual absence of creep.
Due to branching, the size of the ordered polystyrene domains tend
to be small which is believed to lead towards improved stress
transfer (strength), higher toughness, higher modulus, and lower
viscosity.
EXAMPLES
[0050] In order to demonstrate practice of the invention, the
following examples are offered to more fully illustrate the
invention, but are not to be construed as limiting the scope
thereof. Further, while some of examples may include conclusions
about the way the invention may function, the inventors do not
intend to be bound by those conclusions, but put them forth only as
possible explanations. Moreover, unless noted by use of past tense,
presentation of an example does not imply that an experiment or
procedure was, or was not, conducted, or that results were, or were
not actually obtained. Efforts have been made to ensure accuracy
with respect to numbers used (e.g., amounts, temperature), but some
experimental errors and deviations may be present. Unless indicated
otherwise, parts are parts by weight, molecular weight is number
average molecular weight, temperature is in degrees Centigrade, and
pressure is at or near atmospheric.
[0051] The scheme below outlines the synthesis route taken to
arrive at PSt-g-P(IB-b-St):
##STR00001##
[0052] Acetyl-chloride (AcCl), aluminum chloride (AlCl.sub.3),
magnesium sulfate (MgSO.sub.4), titanium chloride (TiCl.sub.4),
styrene and polystyrene of Mn=35,000 were obtained from Merck.
Tetramethylethylene diamine (TMEDA) and methyl magnesium bromide
(MeMgBr) solution were obtained from Sigma Aldrich and were used
without further purification. Isobutylene (IS) was obtained from
Exxon Mobile Co. Methylene chloride (CH.sub.2Cl.sub.2),
tetrahydrofuran (THF) (or alternatively, water) and hexane (from
TCI) were all distilled over calcium hydride prior to use.
[0053] The acetylated polystyrene (PS) starting material was
prepared as follows: A 250 mL flask equipped with a 50 mL addition
funnel and a stir bar and containing anhydrous AlCl.sub.3 (0.23 g,
1.7 mmol) was evacuated and protected by a blanket of gaseous
N.sub.2. Then, 20 ml CH.sub.2Cl.sub.2 was then transferred into the
flask via a capillary by nitrogen pressure. The mixture was then
cooled to 0.degree. C., and AcCl (0.120 mL, 1.7 mmol) dissolved in
5 mL CH.sub.2Cl.sub.2 was then added dropwise from the addition
funnel into the AlCl.sub.3 solution during a 10 minute period.
Then, polystyrene (10 g, Mn=35,000 g/mol, 0.20 mmol) dissolved in
100 mL of CH.sub.2Cl.sub.2 was added, and the reaction was then
allowed to proceed for 15 minutes at room temperature. The product
obtained is then poured into a beaker containing approximately 10
of ice and 5 mL of concentrated HCl. Then, the inorganic layer
formed is separated and washed successively with water and a 5%
sodium bicarbonate solution. Once separated and washed, the
inorganic layer is dried overnight over anhydrous MgSO.sub.4. A
rotary evaporator then concentrated the solution and the product
formed is precipitated into excess methanol. The yield obtained was
10.07 g, which equates to approximately 99% acetylation.
[0054] The acetylated PS was characterized by .sup.1H NMR
spectroscopy, which showed the expected structure, and GPC, which
indicates that the Mn of the product did not change. This process
introduces an estimated 6 acetyl groups per PS molecule, i.e., the
grafting density is 6.
[0055] The acetyl groups (--COCH.sub.3) of the acetylated PS were
converted to --C(CH.sub.3).sub.2OH groups (indicated as
intermediate a in Scheme 1) as follows. 10.07 g of the acetylated
PS was dissolved in 120 mL of anhydrous THF contained in a 500 mL
round bottom flask. 1.2 mL of 3.0 M MeMgBr in diethyl ether is
syringed dropwise into the polymer solution under N.sub.2 gas.
After one hour, the reaction mixture was cooled to 0.degree. C.,
and then 2 Ml of 3 M HCl was added dropwise. The organic phase was
then separated, washed with 20 mL of aqueous NaCl, dried over
anhydrous CaCl.sub.2, concentrated by a rotary evaporator, and
precipitated into excess methanol. The yield obtained was
approximately 10.10 g, which equates to approximately 99%
completion of reaction.
[0056] The --C(CH.sub.3).sub.2OH groups are converted into
--C(CH.sub.3).sub.2Cl groups (indicated as intermediate b in Scheme
1) as follows. Intermediate a (PSt with --C(CH.sub.3).sub.2OH
groups, 10.10 g, 0.29 mmole) was placed in a Schlenk flask and
dissolved in methylene chloride (100 mL) under a blanket of N.sub.2
gas. The solution was then transferred by use of a stainless steel
capillary into a flame dried 200 mL tubular reactor containing
approximately 0.1 g CaCl.sub.2. Gaseous HCl (generated by dropwise
addition of sulfuric acid onto NaCl) was then bubbled into the
solution using a Teflon capillary for six hours at 0.degree. C.
under a continuous nitrogen flush. The excess HCl was neutralized
by absorbing the gas in aqueous sodium hydroxide. Then, the
CaCl.sub.2 was filtered off; the solution was concentrated by
rotary evaporation; diluted with 100 mL of hexane; and washed with
a solution of 5% aqueous sodium bicarbonate and water. The hexane
layer was separated and then dried over MgSO.sub.4. The drying
agent was then filtered off and the solution was concentrated and
precipitated in excess cold methanol. The resultant precipitate was
separated by filtration, dried under vacuum at room temperature,
and stored under nitrogen at -20.degree. C. The yield obtained was
approximately 10.12 g, which equates to approximately 99%
completion of reaction.
[0057] The --C(CH.sub.3).sub.2OH groups were converted into
--C(CH.sub.3).sub.2OMe groups (indicated as intermediate c in
Scheme 1) as follows. Intermediate a (PSt with
--C(CH.sub.3).sub.2OH groups, 10.10 g, 0.29 mmole) was placed in a
Schlenk flask and dissolved in THF (100 mL) under a blanket of
N.sub.2 gas. Then, NaH (0.082 g, 3.4 mmol) dissolved in 20 mL of
THF was added dropwise for one hour at 0.degree. C. under a
nitrogen atmosphere. Next, CH.sub.3I (0.32 mL, 5.1 mmol) dissolved
in 10 mL of dried THF was added dropwise at 0.degree. C. The
solution was then stirred for 2 hours at 25.degree. C.,
concentrated by a rotary evaporator, and precipitated into excess
methanol. The yield obtained was approximately 10.11 g, which
equates to approximately 99% completion of the reaction.
[0058] If beginning with intermediate a, (PSt with
--C(CH.sub.3).sub.2OH groups), the final steps of living block
polymerization of isobutylene followed by styrene will be carried
out first with the addition of isobutylene in the presence of a
co-initiator such as TiCl.sub.4. Subsequently, once the
polymerization of the isobutylene has been completed, styrene will
be added to the active polymer solution. Once the polymerization of
the styrene has been completed, the polymerization will be
terminated, the polymer will be washed and then dried; all solvents
will then be removed and the final product, PSt-g-P(IB-b-St), will
be collected.
[0059] When beginning with intermediate b, (PSt with
--C(CH.sub.3).sub.2Cl groups), the final steps of living block
polymerization of isobutylene followed by styrene is carried out as
follows. 1.5 g (0.043 mmol) of intermediate b was placed into a 500
mL round bottom flask equipped with a magnetic stir bar, the flask
was evacuated and blanketed with N.sub.2 gas. Next, 120 mL hexane
and 80 mL of dichloromethane was added by a stainless steel
capillary, and then TMEDA (0.078 mL, 0.52 mmol) was added by
syringe under an N.sub.2 atmosphere. The system was then cooled to
-80.degree. C. Then, IS (10.3 mL, 0.14 mol) was added, followed by
the addition of TiCl.sub.4 (0.29 mL, 2.61 mmol). The polymerization
was allowed to proceed for one hour. Subsequently, styrene (4.31
mL, 37.6 mmol) was transferred into the active polymer solution.
The polymerization of the added styrene was allowed to proceed for
one hour and was terminated with the addition of 10 ml of methanol.
The system was then warmed to room temperature, the solution was
decanted, the polymer was dissolved in hexane, and then washed with
5% aqueous sodium bicarbonate and water. The organic phase was then
dried overnight over magnesium sulfate, the solids were then
removed by filtering through fine sintered glass. The solvent was
removed by evaporation by use of a rotary evaporator. The product,
PSt-g-P(IB-b-St), was then dried in a vacuum oven at 50.degree. C.
for 2 days. The yield obtained was approximately 13.11 g, which
equates to approximately 99% completion of reaction.
[0060] When beginning with intermediate c, (PSt with
--C(CH.sub.3).sub.2OMe groups), the final steps of living block
polymerization of isobutylene followed by styrene is carried out
first with the addition of isobutylene in the presence of a
co-initiator such as TiCl.sub.4. Subsequently, once the
polymerization of the isobutylene has been completed, styrene will
be added to the active polymer solution. Once the polymerization of
the styrene has been completed, the polymerization will be
terminated, the polymer will be washed and then dried; all solvents
will then be removed and the final product, PSt-g-P(IB-b-St), will
be collected.
[0061] Regardless of what intermediate is used, the final product
of PSt-g-P(IB-b-St) can then be characterized by NMR spectroscopy,
which will show the presence of both the PIS and PSt. The
PSt-g-P(IB-b-St) created using intermediate b, as discussed above,
showed high tensile strength elongation, toughness, and a low creep
and the Inventors believe that PSt-g-P(IB-b-St) created using
intermediate a or c will also show high tensile strength
elongation, toughness, and a very low creep.
[0062] The same procedure as described above was repeated, except
that the amount of styrene used during the final step of living
block polymerization was increased. In this second example, the
amount of styrene used was 5.7 mL (50.12 mmol) as compared to the
4.31 mL (37.6 mmol) used in the example above creating
PSt-g-P(IB-b-St) using intermediate b. The composition and
molecular architecture, respectively, of the two PSt-g-P(IB-b-St)
formed are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Mn (g/mol) .times. 10.sup.-3 PSt-
Composition (wt %) Example PSt.sub.bb PIB.sub.br PSt.sub.br
g-P(IB-b-St).sub.6** PSt.sub.bb PIB.sub.br PSt.sub.br 1 35 30 15
305 11.5 59.0 29.5 2 35 30 20 335 11.5 53.7 35.8 bb in the
subscript is backbone and br in the subscript is branch **indicated
the number of arms per PSt backbone
[0063] The PSt-g-P(IB-b-St) formed from Example 2 was characterized
by NMR spectroscopy, which showed the presence of both the PIS and
PSt. The PSt-g-P(IB-b-St) showed high tensile strength elongation,
toughness, and a very low creep.
[0064] In light of the foregoing, it should be appreciated that the
present invention significantly advances the art by providing a
novel structure and synthesis of a
polystyrene-g-(polyisobutylene-b-polystyrene) PSt-g-P(IB-b-St) that
is structurally and functionally improved in a number of ways.
While particular embodiments of the invention have been disclosed
in detail herein, it should be appreciated that the invention is
not limited thereto or thereby inasmuch as variations on the
invention herein will be readily appreciated by those of ordinary
skill in the art. The scope of the invention shall be appreciated
from the claims that follow.
* * * * *