U.S. patent application number 13/284016 was filed with the patent office on 2012-02-23 for gas separation using membranes comprising polybenzoxazoles prepared by thermal rearrangement.
This patent application is currently assigned to INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY. Invention is credited to Sang Hoon Han, Chul-Ho Jung, Keun-Young Kim, Hye Jin Kwon, Young Moo LEE, Ho-Bum Park.
Application Number | 20120042777 13/284016 |
Document ID | / |
Family ID | 41065388 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120042777 |
Kind Code |
A1 |
LEE; Young Moo ; et
al. |
February 23, 2012 |
GAS SEPARATION USING MEMBRANES COMPRISING POLYBENZOXAZOLES PREPARED
BY THERMAL REARRANGEMENT
Abstract
A method of separating components of a gas mixture, the method
comprising: passing the gas mixture through a benzoxazole-based
polymer membrane at a temperature of from about 30.degree. C. to
about 400.degree. C., wherein the benzoxazole-based polymer
membrane is represented by the formula: ##STR00001## as is defined
herein.
Inventors: |
LEE; Young Moo; (Seoul,
KR) ; Kim; Keun-Young; (Seoul, KR) ; Jung;
Chul-Ho; (Gwangju, KR) ; Park; Ho-Bum; (Seoul,
KR) ; Kwon; Hye Jin; (Seoul, KR) ; Han; Sang
Hoon; (Seoul, KR) |
Assignee: |
INDUSTRY-UNIVERSITY COOPERATION
FOUNDATION HANYANG UNIVERSITY
Seoul
KR
|
Family ID: |
41065388 |
Appl. No.: |
13/284016 |
Filed: |
October 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12921980 |
Sep 10, 2010 |
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PCT/KR2008/001419 |
Mar 13, 2008 |
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13284016 |
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Current U.S.
Class: |
95/47 ; 528/185;
95/50; 95/51 |
Current CPC
Class: |
C08G 73/22 20130101;
C08L 79/04 20130101; C01B 2203/0405 20130101; B01D 2325/24
20130101; B01D 71/62 20130101; C01B 3/503 20130101; C01B 2203/0475
20130101; C01B 2203/048 20130101; B01D 53/228 20130101; B01D
2325/22 20130101; B01D 69/02 20130101 |
Class at
Publication: |
95/47 ; 528/185;
95/51; 95/50 |
International
Class: |
C08G 73/22 20060101
C08G073/22; B01D 53/22 20060101 B01D053/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2008 |
KR |
10-2008-0022970 |
Claims
1. A method of separating H.sub.2 and CO.sub.2 from a gas mixture,
the method comprising: passing the gas mixture comprising H.sub.2
and CO.sub.2 through a benzoxazole-based polymer membrane at a
temperature of from about 30.degree. C. to about 400.degree. C.,
wherein the benzoxazole-based polymer membrane is represented by
the formula: ##STR00034## wherein Ar is a bivalent C.sub.5-C.sub.24
arylene group or a bivalent C.sub.5-C.sub.24 heterocyclic ring,
which is substituted or unsubstituted with at least one substituent
selected from the group consisting of C.sub.1-C.sub.10 alkyl,
C.sub.1-C.sub.10 alkoxy, C.sub.1-C.sub.10 haloalkyl and
C.sub.1-C.sub.10 haloalkoxy, or two or more of which are fused
together to form a condensation ring, or covalently bonded to each
other via a functional group selected from the group consisting of
O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2 and C(.dbd.O)NH; Q is a single bond, O, S,
C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3),
C.sub.1-C.sub.6 alkyl-substituted phenyl or C.sub.1-C.sub.6
haloalkyl-substituted phenyl in which Q is linked to opposite both
phenyl rings in the position of m-m, m-p, p-m or p-p; and n is an
integer of 20 to 400.
2. The method of claim 1, wherein Ar is selected from the following
compounds: ##STR00035## wherein X is O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; Y is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical or different and are O, N or S.
3. The method of claim 1, wherein Ar is selected from the following
compounds: ##STR00036## ##STR00037## ##STR00038## ##STR00039##
##STR00040## ##STR00041## ##STR00042## ##STR00043##
##STR00044##
4. The method of claim 1, wherein Q is a single bond,
C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(.dbd.O)NH,
C(CH.sub.3)(CF.sub.3), ##STR00045##
5. The method of claim 1, wherein Ar is ##STR00046## and Q is
C(CF.sub.3).sub.2.
6. A method of separating a pair of gasses from a gas mixture
comprising the pair of gases, the method comprising: passing the
gas mixture through a benzoxazole-based polymer membrane at a
temperature of from about 30.degree. C. to about 400.degree. C.,
wherein the benzoxazole-based polymer membrane is represented by
the formula: ##STR00047## wherein Ar is a bivalent C.sub.5-C.sub.24
arylene group or a bivalent C.sub.5-C.sub.24 heterocyclic ring,
which is substituted or unsubstituted with at least one substituent
selected from the group consisting of C.sub.1-C.sub.10 alkyl,
C.sub.1-C.sub.10 alkoxy, C.sub.1-C.sub.10 haloalkyl and
C.sub.1-C.sub.10 haloalkoxy, or two or more of which are fused
together to form a condensation ring, or covalently bonded to each
other via a functional group selected from the group consisting of
O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2 and C(.dbd.O)NH; Q is a single bond, O, S,
C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3),
C.sub.1-C.sub.6 alkyl-substituted phenyl or C.sub.1-C.sub.6
haloalkyl-substituted phenyl in which Q is linked to opposite both
phenyl rings in the position of m-m, m-p, p-m or p-p; and n is an
integer of 20 to 400, wherein the gas pair is selected from the
group consisting of H.sub.2/CH.sub.4, H.sub.2/CO.sub.2,
H.sub.2/N.sub.2, He/N.sub.2, O.sub.2/N.sub.2, CO.sub.2/N.sub.2, and
CO.sub.2/CH.sub.4.
7. The method of claim 6, wherein Ar is selected from the following
compounds: ##STR00048## wherein X is O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; Y is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical or different and are O, N or S.
8. The method of claim 6, wherein Ar is selected from the following
compounds: ##STR00049## ##STR00050## ##STR00051## ##STR00052##
##STR00053## ##STR00054## ##STR00055## ##STR00056##
##STR00057##
9. The method of claim 6, wherein Q is a single bond,
C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(.dbd.O)NH,
C(CH.sub.3)(CF.sub.3), ##STR00058##
10. The method of claim 6, wherein Ar is ##STR00059## and Q is
C(CF.sub.3).sub.2.
11. A gas separation membrane comprising polybenzoxazole
(TR-.beta.-PBO) represented by the formula: ##STR00060## wherein Ar
is a bivalent C.sub.5-C.sub.24 arylene group or a bivalent
C.sub.5-C.sub.24 heterocyclic ring, which is substituted or
unsubstituted with at least one substituent selected from the group
consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10 alkoxy,
C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy, or two
or more of which are fused together to form a condensation ring, or
covalently bonded to each other via a functional group selected
from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Q is a single bond, O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; and n is an integer of 20 to 400,
wherein the polybenzoxazole has a weight average molecular weight
of from more than about 50,000 Da to about 300,000 Da.
12. The gas separation membrane of claim 11, wherein the
polybenzoxazole has a weight average molecular weight of from more
than about 50,000 Da to about 200,000 Da.
13. The method of claim 1 wherein the gas mixture is passed through
the benzoxazole-based polymer membrane at a temperature of from
about 200.degree. C. to about 350.degree. C.
14. The method of claim 6 wherein the gas mixture is passed through
the benzoxazole-based polymer membrane at a temperature of from
about 200.degree. C. to about 350.degree. C.
15. The method of claim 1, wherein Ar is ##STR00061## and Q is
C(CF.sub.3).sub.2.
16. The method of claim 1, wherein Ar is ##STR00062## and Q is
C(CF.sub.3).sub.2.
17. The method of claim 6, wherein Ar is ##STR00063## and Q is
C(CF.sub.3).sub.2.
18. The method of claim 6, wherein Ar is ##STR00064## and Q is
C(CF.sub.3).sub.2.
19. The gas separation membrane of claim 11, wherein Ar is
##STR00065## and Q is C(CF.sub.3).sub.2.
20. The gas separation membrane of claim 11, wherein Ar is
##STR00066## and Q is C(CF.sub.3).sub.2.
21. The gas separation membrane of claim 11, wherein Ar is
##STR00067## and Q is C(CF.sub.3).sub.2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 12/921,980, filed on Mar. 13, 2008, the
disclosure of which is incorporated herein by reference in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method for preparing a
benzoxazole-based polymer by thermal rearrangement which is
performed by a simple process and induces thermal rearrangement at
relatively lower thermal conversion temperatures to prepare a
benzoxazole-based polymer suited for application to gas separation
membranes, in particular, to gas separation membranes for small
gases, the benzoxazole-based polymer prepared by the method and a
gas separation membrane comprising the benzoxazole-based
polymer.
BACKGROUND ART
[0003] Free-volume elements in soft organic materials have been
focused upon to improve membrane separation performance in chemical
products as well as for energy conversion and storage applications
[P. M. Budd, N. B. McKeown, D. Fritsch, Polymers with cavities
tuned for fast selective transport of small molecules and ions, J.
Mater. Chem. 2005, 15, 1977; W. J. Koros, Fleming G. K.,
Membrane-based gas separation, J. Membr. Sci. 1993, 83, 1; S. A.
Stern, Polymers for gas separations: The next decade, J. Membr.
Sci. 1994, 94, 1].
[0004] The free volume element size and distribution play a key
role in determining permeability and separation characteristics of
polymers. Among typical polymeric membranes, glassy polymers have
exhibited good gas separation performance with high selectivity,
however, permeability of glassy polymers is poorly suited to
practical applications [M. Langsam, "Polyimide for gas separation,
in Polyimides: fundamentals and applications", Marcel Dekker, New
York, 1996; B. D. Freeman, Basis of permeability/selectivity
tradeoff relations in polymeric gas separation membranes,
Macromolecules 1999, 32, 375].
[0005] Even though some glassy polymers with ultra-high free volume
such as poly(1-trimethylsilyl-1-propyne) (PTMSP),
poly(4-methyl-2-pentyne) (PMP), and copolymers of
2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxide and
tetrafluoroethylene (Teflon.RTM. AF amorphous fluoropolymers)
exhibited extremely high gas permeability, they still had very low
performance in selectivities. [K. Nagai, T. Masuda, T. Nakagawa, B.
D. Freeman, I. Pinnau, Poly[1-(trimethylsilyl)-1-propyne] and
related polymers: Synthesis, properties and functions, Prog. Polym.
Sci. 2001, 26, 721; A. Morisato, I. Pinnau, Synthesis and gas
permeation properties of poly(4-methyl-2-pentyne), J. Membr. Sci.
1996, 121, 243; A. M. Polyakov, L. E. Starannikova, Y. P.
Yampolskii, Amorphous Teflons AF as organophilic pervaporation
materials: Transport of individual components, J. Membr. Sci. 2003,
216, 241].
[0006] A great deal of research has endeavored to produce ideal
structures having precise cavities for high gas permeability and
high gas selectivity. As a result of this research, there has been
remarkable development of polymer membranes exhibiting high
gas-separation performance. For example, designs for
nanocomposites, hybrid materials and complex polymers were
considered to impart large free volume to polymers.
[0007] Of these, methods to realize intermediate and small cavity
size distributions were reported recently [H. B. Park, C. H. Jung,
Y. M. Lee, A. J. Hill, S. J. Pas, S. T. Mudie, E. Van Wagner, B. D.
Freeman, D. J. Cookson, Polymers with cavities tuned for fast
selective transport of small molecules and ions, Science 2007, 318,
254. 38].
[0008] Lee et al. suggested that completely aromatic, insoluble,
infusible polybenzoxazole (TR-.alpha.-PBO) membranes can be
prepared by thermally modifying ortho-hydroxyl group-containing
polyimide aromatic polymers through thermal rearrangement to
molecular rearrangement at 350 to 450.degree. C. [H. B. Park, C. H.
Jung, Y. M. Lee, A. J. Hill, S. J. Pas, S. T. Mudie, E. Van Wagner,
B. D. Freeman, D. J. Cookson, Polymers with cavities tuned for fast
selective transport of small molecules and ions, Science 2007, 318,
254. 38].
[0009] TR-.alpha.-PBO membranes have advantages of excellent gas
separation performance and superior chemical stability and
mechanical properties, surpassing the limitations of typical
polymeric membranes (i.e., the Robeson's upper bound). [L. M.
Robeson, Correlation of separation factor versus permeability for
polymeric membranes, J. Membr. Sci., 1991, 62, 165, L. M. Robeson,
The upper bound revisited, J. Membr. Sci., 2008, 320, 390].
However, in spite of extremely high permeability in CO.sub.2
separation, TR-.alpha.-PBO still exhibits low selectivity for small
gases such as hydrogen and helium.
OBJECTS OF THE INVENTION
[0010] Therefore, it is one object of the present invention to
provide a method for preparing a benzoxazole-based polymer, wherein
the method is performed by a simple process and induces thermal
rearrangement at relatively lower temperatures.
[0011] It is another object of the present invention to provide a
poly(hydroxyamide) intermediate suitable for the preparation of the
benzoxazole-based polymer.
[0012] It is another object of the present invention to provide
polybenzoxazole (TR-.beta.-PBO) having morphological and physical
properties different from conventional polybenzoxazole
(TR-.alpha.-PBO).
[0013] It is another object of the present invention to provide a
poly(hydroxyamide) (PHA) intermediate suitable for the preparation
of the polybenzoxazole (TR-.beta.-PBO).
[0014] It is another object of the present invention to provide a
gas separation membrane comprising the polybenzoxazole
(TR-.beta.-PBO) with high permeability and superior selectivity for
small gases.
[0015] It is another object of the present invention to provide a
method of separating gases at high temperatures by passing a
gaseous mixture through a gas separation membrane comprising a
polybenzoxazole (TR-.beta.-PBO).
SUMMARY OF THE INVENTION
[0016] In accordance with one aspect of the present invention for
achieving the above object, there is provided a method for
preparing a benzoxazole-based polymer represented by Formula 1, by
thermally treating poly(hydroxyamide) represented by Formula 2, as
depicted in Reaction Scheme 1 below:
##STR00002##
[0017] wherein Ar is a bivalent C.sub.5-C.sub.24 arylene group or a
bivalent C.sub.5-C.sub.24 heterocyclic ring, which is substituted
or unsubstituted with at least one substituent selected from the
group consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10
alkoxy, C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy,
or two of more of which are fused together to form a condensation
ring, or covalently bonded to each other via a functional group
selected from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH;
[0018] Q is a single bond, O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; and
[0019] n is an integer of 20 to 400.
[0020] In accordance with another aspect of the present invention,
there is provided a poly(hydroxyamide) intermediate represented by
Formula 2 used in the preparation of the benzoxazole-based polymer
Formula 1.
##STR00003##
[0021] wherein Ar, Q and n are defined as above.
[0022] In accordance with another aspect of the present invention,
there is provided polybenzoxazole (TR-.beta.-PBO) represented by
Formula 3, having a glass transition temperature (Tg) of
377.degree. C. and a d-spacing of 6.0 to 6.10 .ANG..
##STR00004##
[0023] In accordance with another aspect of the present invention,
there is provided a method for preparing polybenzoxazole
(TR-.beta.-PBO, 3) by thermally treating poly(hydroxyamide) (PHA,
8), as depicted in Reaction Scheme 3 below:
##STR00005##
[0024] In accordance with another aspect of the present invention,
there is provided a poly(hydroxyamide) intermediate represented by
the following Formula 8 used for the preparation of the
polybenzoxazole (TR-.beta.-PBO).
##STR00006##
[0025] In accordance with another aspect of the present invention,
there is provided a gas separation membrane comprising
polybenzoxazole (TR-.beta.-PBO) represented by Formula 3 and having
a glass transition temperature (Tg) of 377.degree. C.
##STR00007##
[0026] According to the method of the present invention,
polybenzoxazole is simply prepared by thermally converting
poly(hydroxyamide) as an intermediate via thermal treatment at low
temperatures. The polybenzoxazole thus prepared exhibits superior
mechanical and morphological properties and has well-connected
microcavities, thus showing excellent permeability and selectivity
for various types of gases.
[0027] The polybenzoxazole is suited for application to gas
separation membranes, in particular, gas separation membranes for
small gases, e.g. H.sub.2/CH.sub.4, H.sub.2/CO.sub.2,
H.sub.2/N.sub.2, He/N.sub.2, O.sub.2/N.sub.2, CO.sub.2/N.sub.2, and
CO.sub.2/CH.sub.4.
[0028] In yet another aspect, the present invention provides a
method of separating H.sub.2 and CO.sub.2 from a gas mixture, the
method comprising: passing the gas mixture comprising H.sub.2 and
CO.sub.2 through a benzoxazole-based polymer membrane at a
temperature of from about 30.degree. C. to about 400.degree. C.,
wherein the benzoxazole-based polymer membrane is represented by
the formula:
##STR00008##
wherein Ar is a bivalent C.sub.5-C.sub.24 arylene group or a
bivalent C.sub.5-C.sub.24 heterocyclic ring, which is substituted
or unsubstituted with at least one substituent selected from the
group consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10
alkoxy, C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy,
or two or more of which are fused together to form a condensation
ring, or covalently bonded to each other via a functional group
selected from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Q is a single bond, O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; and n is an integer of 20 to
400.
[0029] In still yet another aspect, the present invention provides
a gas separation membrane comprising polybenzoxazole
(TR-.beta.-PBO) represented by the formula:
##STR00009##
wherein Ar is a bivalent C.sub.5-C.sub.24 arylene group or a
bivalent C.sub.5-C.sub.24 heterocyclic ring, which is substituted
or unsubstituted with at least one substituent selected from the
group consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10
alkoxy, C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy,
or two or more of which are fused together to form a condensation
ring, or covalently bonded to each other via a functional group
selected from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Q is a single bond, O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; and n is an integer of 20 to 400,
wherein the polybenzoxazole has a weight average molecular weight
of from over about 50,000 Da to about 300,000 Da.
DESCRIPTION OF THE DRAWINGS
[0030] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0031] FIG. 1 is graphs showing TGA-MS results of the PHA precursor
membrane of Example 1 and the HPI precursor membrane of Comparative
Example 1;
[0032] FIG. 2(a) is FT-IR spectra of the HPI precursor membrane and
the TR-.alpha.-PBO membrane of Comparative Example 1 and FIG. 2(b)
is FT-IR spectra of the PHA precursor membrane and TR-.beta.-PBO
membrane of Example 1;
[0033] FIG. 3 is DSC thermograms of the PHA precursor membrane and
the TR-.beta.-PBO membrane Example 1 and the HPI precursor membrane
and the TR-.alpha.-PBO membrane of Comparative Example 1;
[0034] FIG. 4(a) is X-ray diffraction patterns of the HPI precursor
membrane and the TR-.alpha.-PBO membrane of Comparative Example 1
and FIG. 4(b) is X-ray diffraction patterns of the PHA precursor
membrane and the TR-.beta.-PBO membrane of Example 1;
[0035] FIG. 5(a) is adsorption isotherms of constant-pressure
simulations for O.sub.2 and FIG. 5(b) is adsorption isotherms of
constant-pressure simulations for N.sub.2;
[0036] FIG. 6 is N.sub.2 adsorption/desorption isotherms at
-196.degree. C. for the HPI precursor membrane (a) and the
TR-.alpha.-PBO membrane (b) of Comparative Example 1, and the PHA
precursor membrane (c) and TR-.beta.-PBO membrane (d) of Example
1;
[0037] FIG. 7(a) is a graph showing H.sub.2
permeability-H.sub.2/N.sub.2 selectivity of the TR-.beta.-PBO
membrane and conventional polymer membranes and FIG. 7(b) is a
graph showing H.sub.2 permeability-H.sub.2/CH.sub.4 selectivity of
the TR-.beta.-PBO membrane and conventional polymer membranes;
[0038] FIG. 8 illustrates IR spectra of certain PHAs according to
the present invention;
[0039] FIGS. 9(a), (b), and (c) illustrate the thermogravimetric
analysis with trace of m/e 18 (H.sub.2O) (TG-MS) of certain
PHAs;
[0040] FIG. 10 illustrates IR spectra of certain TR-.beta.-PBOs
according to the present invention;
[0041] FIGS. 11(a), (b), and (c) illustrate the cavity diameters
and intensities measured by positron annihilation lifetime
spectroscopy (PALS) for (a) 6FIP, (b) 6FTP and (c) 6F6F membranes
treated from 250 to 350.degree. C.;
[0042] FIGS. 12(a) and (b) illustrate wide-angle X-ray diffraction
(WAXD) patterns of certain PHAs and TR-.beta.-PBOs according to the
present invention;
[0043] FIGS. 13(a), (b), and (c) illustrate the trade-off
relationships in PHAs and TR-.beta.-PBOs for (a) O.sub.2/N.sub.2,
(b) CO.sub.2/CH.sub.4 and (c) H.sub.2/CO.sub.2 at 300K;
[0044] FIGS. 14(a) and (b) illustrate the temperature dependence on
cavity diameters and intensities for 5a membrane by PALS (a) .tau.3
and (b) .tau.4; and
[0045] FIGS. 15(a) and (b) illustrate the temperature dependence on
H.sub.2 permeability and H.sub.2/CO.sub.2 selectivity of
TR-.beta.-PBO membranes at 20 bar (a) with temperature variation
(filled: H.sub.2 permeability, empty: H.sub.2/CO.sub.2
selectivity), (b) with polymeric upper bounds.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS THE INVENTION
[0046] Hereinafter, the present invention will be illustrated in
more detail.
[0047] The preparation method of the present invention comprises
thermally converting poly(hydroxyamide) into polybenzoxazole
through thermal treatment involving dehydration.
[0048] Specifically, the poly(hydroxyamide) represented by Formula
2 as a precursor is converted into the benzoxazole-based polymer
represented by Formula 1, as depicted in Reaction Scheme 1
below:
##STR00010##
wherein Ar is a bivalent C.sub.5-C.sub.24 arylene group or a
bivalent C.sub.5-C.sub.24 heterocyclic ring, which is substituted
or unsubstituted with at least one substituent selected from the
group consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10
alkoxy, C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy,
or two or more of which are fused together to form a condensation
ring, or covalently bonded to each other via a functional group
selected from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH;
[0049] Q is a single bond, O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; and
[0050] n is an integer of 20 to 400.
[0051] Preferably, Ar is selected from the following compounds and
the linkage position thereof includes all of o-, m- and
p-positions.
##STR00011##
[0052] wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; Y is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical or different and are O, N or S.
[0053] More preferably, Ar is selected from the following
compounds:
##STR00012## ##STR00013## ##STR00014## ##STR00015## ##STR00016##
##STR00017## ##STR00018## ##STR00019## ##STR00020##
[0054] In Formula 1, Q is a single bond, C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3),
##STR00021##
[0055] More preferably, Ar is
##STR00022##
and Q is C(CF.sub.3).sub.2.
[0056] As can be seen from Reaction Scheme 1, the
poly(hydroxyamide) 2 as a precursor is converted into the
benzoxazole-based polymer 1. The conversion of the
poly(hydroxyamide) 2 into the benzoxazole-based polymer 1 is
carried out by dehydration, namely, removal of H.sub.2O present in
the poly(hydroxyamide) 2.
[0057] After the thermal rearrangement through the thermal
treatment, the benzoxazole-based polymer 1 undergoes morphological
changes including reduced density, considerably increased
fractional free volume (FFV) due to increased microcavity size and
increased d-spacing, as compared to the precursor 2. As a result,
the benzoxazole-based polymer 1 exhibits considerably high gas
permeability, as compared to the precursor 2. In addition, the
benzoxazole-based polymer 1 exhibits improved tensile strength and
elongation.
[0058] These morphological properties can be readily controlled by
a design taking into consideration the characteristics (e.g.,
steric hindrance) of Ar and Q, the functional groups present in the
molecular structures, and permeability and selectivity for various
types of gases can be thus controlled.
[0059] According to the present invention, the thermal treatment is
carried out at 150 to 450.degree. C., preferably 250 to 350.degree.
C., at a heating rate of 1 to 10.degree. C./min for 5 minutes to 12
hours, preferably for 10 minutes to 2 hours, under an inert
atmosphere. When the thermal treatment temperature is less than the
level as defined the above, the thermal rearrangement is
incomplete, thus leaving precursor residues, causing deterioration
of purity. Increasing the thermal treatment temperature above the
level defined above provides no particular advantage, thus being
economically impractical. Accordingly, the thermal treatment is
properly carried out within the temperature range as defined
above.
[0060] At this time, the reaction conditions are properly
controlled according to Ar and Q, the functional groups of the
precursor, and specific conditions can be adequately selected and
modified by those skilled in the art.
[0061] Preferably, the benzoxazole-based polymer 1 is designed in
the preparation process such that it has a desired molecular
weight. Preferably, the weight average molecular weight of the
benzoxazole-based polymer 1 is adjusted to from 10,000 to 300,000
Da. When the weight average molecular weight is less than 10,000
Da, physical properties of the polymer are poor. In certain
preferred embodiments of the present invention, the weight average
molecular weight of the benzoxazole-based polymer 1 is preferably
from more than about 50,000 Da to about 300,000 Da, and more
preferably from more than about 50,000 Da to about 200,000 Da.
Benefits of employing such higher molecular weight
benzoxazole-based polymers as gas separation membranes according to
the present invention include, relative to the lower molecular
weight polymers, increased tensile strength, toughness, flexural
strength, chemical resistance, and thermal resistance.
[0062] In particular, the poly(hydroxyamide) 2 used as a precursor
in the present invention is prepared by a conventional method.
[0063] For example, the poly(hydroxyamide) 2 is prepared by
reacting the compound 4 with the compound 5, as depicted in
Reaction Scheme 2 below:
##STR00023##
[0064] wherein X is a halogen atom, and Ar, Q and n are defined as
above.
[0065] Preferably, the halogen atom is F, Cl, Br or I. More
preferred is the use of Cl in view of its high reactivity.
[0066] For example, terephthaloyl chloride (TCL) and
2,2'-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (bisAPAF) are
used as the compounds of Formulae 4 and 5, respectively.
[0067] The compounds 4 and 5 are suitably selected in conformity
with Ar and Q defined throughout the present specification. Taking
stoichiometry into consideration, the compounds 4 and 5 are used in
a desired molar ratio, preferably, in the range of 1:1 to 2:1, and
more preferably, an excess of the compound 4 is used.
[0068] The reaction is carried out at -10 to 60.degree. C. for 30
minutes to 12 hours until the reaction is fully completed.
[0069] Furthermore, an acid acceptor is added to capture HX
(hydrogen halide, i.e. HCl) produced during the reaction. The acid
acceptor is selected from the group consisting of ethylene oxide,
propylene oxide, magnesium oxide, hydrotalcite, magnesium
carbonate, calcium hydroxide, magnesium silicate and combinations
thereof. Preferably, an excess of the acid acceptor is used, as
compared to HX, the reaction product.
[0070] The benzoxazole-based polymer 1 prepared by the method of
the present invention as mentioned above is suited for application
to gas separation membranes due to superior gas permeability and
selectivity thereof.
[0071] The present invention is not limited to the preparation
method of the gas separation membrane. That is, the gas separation
membrane can be prepared in the form of films or fibers (in
particular, hollow fibers) by a conventional method e.g. casting or
laminating.
[0072] For example, the gas separation membrane made of the
benzoxazole-based polymer 1 is prepared by casting the precursor 2
onto a substrate, followed by thermal treatment, as depicted in
Reaction Scheme 1.
[0073] The benzoxazole-based polymer-comprising gas separation
membrane according to the present invention is prepared by
preparing a polymer precursor and subjecting the precursor to
thermal conversion involving dehydration. Accordingly, in terms of
physical properties, the polybenzoxazole gas separation membrane
according to the present invention is remarkably different from gas
separation membranes made of polybenzoxazole (TR-.alpha.-PBO),
which is prepared by preparing a conventional polymer precursor and
subjecting the precursor to thermal treatment involving removal of
CO.sub.2.
[0074] First, glass transition temperatures (Tg, 400.degree. C. or
higher) of conventional polymers prepared through CO.sub.2 removal
are impossible to measure due to a rigid structure thereof, while
Tg of the polybenzoxazole of the present invention is measured to
be 377.degree. C. (in the case of polybenzoxazole prepared in
Example 1) due to its soft molecular structure, thus being
preferably applicable to gas separation membranes.
[0075] Second, the gas separation membrane of the present invention
is useful for gas separation membranes due to high tensile strength
and elongation thereof (See Table 2).
[0076] Third, in terms of morphological properties, the gas
separation membrane has well-connected microcavities and exhibits a
superior fractional free volume, allowing gases to smoothly pass
though the microcavities (good permeability).
[0077] Fourth, the gas separation membrane has a low d-spacing,
thus exhibiting increased permselectivity for small gases.
[0078] Fifth, the gas separation membrane is useful as a gas
separation membrane for gas pair such as H.sub.2/CH.sub.4,
H.sub.2/CO.sub.2, H.sub.2/N.sub.2, He/N.sub.2, O.sub.2/N.sub.2,
CO.sub.2/N.sub.2, and CO.sub.2/CH.sub.4, preferably, as a gas
separation membrane applicable to gas pair such as
H.sub.2/CH.sub.4, H.sub.2/CO.sub.2, H.sub.2/N.sub.2 and He/N.sub.2,
including small gases such as H.sub.2 or He. These gas separation
membranes have high selectivity for small gases due to their
polymeric microcavities.
[0079] Sixth, the benzoxazole-based polymer according to the
present invention can be designed by modifying functional groups in
the molecular structure thereof, thus being used to prepare various
gas separation membrane products.
[0080] In a preferred embodiment of the present invention, the
polybenzoxazole polymer is polybenzoxazole (TR-.beta.-PBO)
represented by Formula 3 below:
##STR00024##
[0081] The polybenzoxazole (TR-.beta.-PBO, 3) is prepared by
thermally treating the poly(hydroxyamide) (PHA, 8), as depicted in
Reaction Scheme 3 below:
##STR00025##
[0082] The thermal treatment is carried out at 150 to 400.degree.
C., preferably 250 to 350.degree. C., at a heating rate of 1 to
10.degree. C./min, for 30 minutes to 12 hours, preferably for 30
minutes to 2 hours, under an inert atmosphere.
[0083] The precursor poly(hydroxyamide) (PHA, 8) is prepared by
reacting terephthaloyl chloride (TCL, 6) with
2,2'-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (bisAPAF, 7),
as depicted in Reaction Scheme 4 below:
##STR00026##
[0084] The reaction is carried out at -10 to 60.degree. C. for 30
minutes to 12 hours until the reaction is thoroughly completed.
[0085] In addition, an acid acceptor is added to capture HX
(hydrogen halide, e.g., HCl) produced during the reaction. The acid
acceptor is selected from the group consisting of ethylene oxide,
propylene oxide, magnesium oxide, hydrotalcite, magnesium
carbonate, calcium hydroxide, magnesium silicate and combinations
thereof. Preferably, an excess of the acid acceptor is used, as
compared to HX, the reaction product.
[0086] The polybenzoxazole (TR-.beta.-PBO, 3) prepared by thermal
treatment as mentioned above has a glass transition temperature
(Tg) of 377.degree., a d-spacing of 6.0 to 6.10 .ANG. and a rigid
rod-type structure.
[0087] The polybenzoxazole (TR-.beta.-PBO, 3) of the present
invention is prepared from the poly(hydroxyamide) precursor and
thus has mechanical and morphological properties different from
conventional polybenzoxazole (conventionally known as
TR-.alpha.-PBO) (See Table 2).
[0088] That is to say, the TR-.alpha.-PBO is prepared by thermally
treating polyimide as a precursor. Tg of the TR-.alpha.-PBO is
impossible to measure. On the other hand, Tg of the TR-.beta.-PBO
of the present invention is observed at 377.degree. C., as
mentioned above. The observable Tg means that the TR-.beta.-PBO has
soft polymeric chains, which affects mechanical properties such as
tensile strength and elongation.
[0089] Furthermore, the TR-.beta.-PBO has a superior fractional
free volume (FFV) property and a d-spacing of 6.0 to 6.10 .ANG.,
preferably 6.02 .ANG., which is different from the d-spacing (i.e.,
6.25 .ANG.) of TR-.alpha.-PBO. The difference in d-spacing affects
gas permeability and selectivity when used for gas separation
membranes.
[0090] Consequently, the conventional TR-.alpha.-PBO and the
present TR-.beta.-PBO have identical repeating units, but have
different physical properties, thus providing greatly different
effects when used for gas separation membranes. This is achieved by
thermally treating the present precursor in the range of specific
temperatures. Preferably, the thermal treatment is carried out at
150 to 450.degree. C., preferably 250 to 350.degree. C., at a
heating rate of 1 to 10.degree. C./min, for 5 minutes to 12 hours,
preferably for 10 minutes to 2 hours, under an inert atmosphere.
When the temperature is less than the level as defined the above,
thermal rearrangement does not proceed to completion, thus leaving
precursor residues, which reduces purity. Exceeding the temperature
as defined above provides no significant advantage and is this
economically disadvantageous. Accordingly, the thermal treatment is
properly carried out within the temperature range as defined
above.
[0091] In particular, the gas separation membrane comprising the
TR-.beta.-PBO of Formula 3 is prepared by a conventional method. In
one embodiment, the method comprises reacting terephthaloyl
chloride (TCL) with 2,2'-bis(3-amino-4-hydroxyphenyl)
hexafluoropropane (bisAPAF) to prepare poly(hydroxyamide) (PHA);
casting the poly(hydroxyamide) (PHA) on a substrate, followed by
drying, to prepare a precursor membrane; and thermally treating the
precursor membrane.
[0092] The drying is carried out at 50 to 200.degree. C. for 30
minutes to 5 hours. The thermal treatment is carried out at 150 to
450.degree. C., preferably at 250 to 350.degree. C., at a heating
rate of 1 to 10.degree. C./min, for 5 minutes to 12 hours,
preferably for 10 minutes to 2 hours under an inert atmosphere.
[0093] The TR-.beta.-PBO gas separation membrane thus prepared
exhibits superior physical properties (e.g., tensile strength of 85
to 90 MPa and elongation of 5 to 10%).
[0094] The TR-.beta.-PBO gas separation membrane is useful as a gas
separation membrane applicable to gas pair such as
H.sub.2/CH.sub.4, H.sub.2/CO.sub.2, H.sub.2/N.sub.2, He/N.sub.2,
O.sub.2/N.sub.2, CO.sub.2/N.sub.2, and CO.sub.2/CH.sub.4,
preferably, as gas separation membranes applicable to gas pairs
such as H.sub.2/CH.sub.4, H.sub.2/CO.sub.2, H.sub.2/N.sub.2, and
He/N.sub.2, including small gases such as H.sub.2 or He. Due to
polymeric microporous properties thereof, the TR-.beta.-PBO gas
separation membrane has high selectivity for small gas series,
which cannot be realized by conventional TR-s separation membrane
ables 6 and 7).
[0095] Moreover, the TR-.beta.-PBO gas separation membranes
according to the present invention are useful as a gas separation
membrane for high temperature separations applicable to gas pairs
such as H.sub.2/CH.sub.4, H.sub.2/CO.sub.2, H.sub.2/N.sub.2,
He/N.sub.2, O.sub.2/N.sub.2, CO.sub.2/N.sub.2, and
CO.sub.2/CH.sub.4, preferably, as high temperature gas separation
membranes applicable to gas pair such as H.sub.2/CH.sub.4,
H.sub.2/CO.sub.2, H.sub.2/N.sub.2, and He/N.sub.2, including small
gases such as H.sub.2 or He. As used herein, the term "high
temperature" as it relates to gas separation refers to temperatures
of from about 30.degree. C. to about 400.degree. C., and preferably
from about 200.degree. C. to about 350.degree. C.
[0096] TR-bet.alpha.-PBO gas separation membranes according to the
present invention can take the physical form of various
configurations well known in the art such as, for example, the form
of hollow fibers, films, tubular shapes, as flat sheets in spiral
wound configurations, or plate and frame configurations. The
following examples demonstrate certain embodiments of high
temperature gas separation according to the present invention.
EXAMPLES
[0097] Hereinafter, preferred examples will be provided for a
further understanding of the invention. These examples are for
illustrative purposes only and are not intended to limit the scope
of the present invention.
Example 1
Preparation of polybenzoxazole (TR-.beta.-PBO) separation
membrane
[0098] TR-.beta.-PBO represented by Formula 3 below was prepared
through the following reaction.
##STR00027##
[0099] 2,2'-bis(3-amino-4-hydroxyphenyl) hexafluoropropane
(bisAPAF, 3.663 g, 10 mmol) and NMP (15.06 mL) were charged into a
100 mL 3-neck flask under nitrogen purging and the mixture was
placed into an ice bath at 0.degree. C. Subsequently, a solution of
propylene oxide (PO, 0.3 mL) and terephthaloyl chloride (TCL, 2.030
g, 10 mmol) in NMP (8.35 mL) was added to the mixture and then
allowed to proceed for 2 hours.
[0100] The resulting mixture was stirred for 12 hours under an
inert atmosphere to obtain a viscous poly(hydroxyamide) (PHA)
solution.
[0101] The solution was cast onto a glass substrate and dried at
100.degree. C. for one hour and at 200.degree. C. for 10 hours to
remove the solvent, thereby obtaining a PHA precursor membrane.
[0102] The PHA precursor membrane was thermally treated at
350.degree. C. at a heating rate of 5.degree. C./min for one hour
under an Ar atmosphere and was then allowed to slowly cool to
ambient temperature to prepare a polybenzoxazole (TR-.beta.-PBO)
separation membrane.
Comparative Example 1
Preparation of Polybenzoxazole (Tr-.alpha.-PBO) Separation
Membrane
[0103] TR-.alpha.-PBO was prepared in accordance with the following
Reaction Scheme 5.
##STR00028##
[0104] BisAPAF (3.663 g, 10 mmol) and NMP (21.34 mL) were charged
into a 100 mL 3-neck flask under nitrogen purging. A solution of
1,2,4,5-benzenetetracarboxylic dianhydride (PMDA, 2.181 g, 10 mmol)
in NMP (12.71 mL) was added thereto. The mixture was allowed to
react at ambient temperature for 5 hours to obtain a viscous yellow
solution. The reaction was allowed to proceed for an additional 12
hours to obtain a polyamic acid (PAA) solution.
[0105] The polyamic acid (PAA) solution was cast onto a glass
substrate and then thermally treated at 100.degree. C. for one hour
and at 300.degree. C. for one hour under reduced pressure to remove
the solvent, thereby obtaining a hydroxy-containing polyimide (HPI)
precursor membrane.
[0106] The HPI precursor membrane was thermally treated at
450.degree. C. with a heating rate of 5.degree. C./min for one hour
under an Ar atmosphere and was then allowed to slowly cool to
ambient temperature to obtain a polybenzoxazole (TR-.alpha.-PBO)
separation membrane.
TABLE-US-00001 TABLE 1 Example 1 Comparative Example 1 Heating
350.degree. C., 1 hour 450.degree. C., 1 hour conditions
Intermediate ##STR00029## PHA ##STR00030## HPI Finally produced PBO
##STR00031## TR-.beta.-PBO ##STR00032## TR-.alpha.-PBO
[0107] The physical properties were evaluated for TR-.beta.-PBO and
TR-.alpha.-PBO separation membranes prepared in Example 1 and
Comparative Example 1 and precursor membranes thereof.
Experimental Example 1
Thermogravimetric Analysis/Mass Spectroscopy (TGA-MS)
[0108] The PHA precursor membrane of Example 1 and the HPI
precursor membrane of Comparative Example 1 were subjected to
TGA-MS to confirm dehydration and CO.sub.2 evolution. The TGA-MS
for each precursor membrane was carried out using TG 209 F1 Iris
and QMS 403C Aeolos (NETZSCH, Germany). The results thus obtained
are shown in FIG. 1.
[0109] FIG. 1 is a graph showing TGA-MS results of the PHA
precursor membrane of Example 1 and the HPI precursor membrane of
Comparative Example 1.
[0110] As can be confirmed from FIG. 1, the PHA precursor membrane
of Example 1 undergoes weight loss at 250 to 350.degree. C.
(represented by reference numeral a' in FIG. 1) corresponding to
the temperature at which thermal conversion from PHA to
TR-.beta.-PBO occurs, and MS peaks indicating dehydration (removal
of H.sub.2O) are plotted at 300.degree. C. (represented by
reference numeral b in FIG. 1). On the other hand, it can be
confirmed from FIG. 1 that the HPI precursor membrane of
Comparative Example 1 undergoes weight loss at 350 to 450.degree.
C. (represented by reference numeral b in FIG. 1) corresponding to
the temperature at which thermal conversion from PHA to
TR-.beta.-PBO occurs, and MS peaks indicating evolution of CO.sub.2
are plotted at about 450.degree. C. (represented by reference
numeral c in FIG. 1).
[0111] These TGA-MS results show that all TR-.alpha.-PBO and
TR-.beta.-PBO membranes are thermally stable up to a maximum
500.degree. C.
Experimental Example 2
FT-IR analysis
[0112] The PHA precursor membrane and TR-.beta.-PBO membrane of
Example 1, and HPI precursor membrane and TR-.alpha.-PBO membrane
of Comparative Example 1 were subjected to FT-IR analysis to
confirm characteristic peaks. FT-IR spectra were obtained using a
Nicolet Magna IR 860 instrument (thermo Nicolet, Madison, Wis.,
USA). The results thus obtained are shown in FIGS. 2(a) and
2(b).
[0113] FIG. 2(a) is FT-IR spectra of the HPI precursor membrane and
the TR-.alpha.-PBO membrane of Comparative Example 1. FIG. 2(b) is
FT-IR spectra of the PHA precursor membrane and TR-.beta.-PBO
membrane of Example 1.
[0114] As can be seen from FIGS. 2(a) and 2(b), broad bands (a and
f) by O--H stretching of HPI and PHA are observed at 3,700 to 2,500
cm.sup.-1.
[0115] As apparent from FIG. 2(a), the HPI precursor membrane shows
characteristic absorption bands of imide groups at 1,729 cm.sup.-1
(C.dbd.O stretching, c) and 1,781 cm.sup.-1 (C.dbd.O stretching,
b), and as apparent from FIG. 2(b), the PHA precursor membrane
shows characteristic absorption peaks of amide groups at 1,650
cm.sup.-1 (C.dbd.O stretching, g) and 1,530 cm.sup.-1 (N--H
bending, h).
[0116] In addition, after thermal conversion into PBO, all of the
TR-.alpha.-PBO and TR-.beta.-PBO membranes show peaks corresponding
to benzoxazole rings at 1,058 cm.sup.-1 (C--O stretching, e, j),
1,480 cm.sup.-1 and 1,558 cm.sup.-1 (C.dbd.N stretching, d, i).
Experimental Example 3
Element Analysis
[0117] The PHA precursor membrane and TR-.beta.-PBO membrane of
Example 1, and the HPI precursor membrane and the TR-.alpha.-PBO
membrane of Comparative Example 1 were subjected to element
analysis (EA) to confirm elements present in the membrane. The
element analysis was carried out using an elemental analyzer (Flash
EA 1112, CE Instruments, UK). The results thus obtained are shown
in Table 2 below.
TABLE-US-00002 TABLE 2 Type Formula C (wt. %) H (wt. %) N (wt. %)
Exam. 1 PHA precursor membrane
[C.sub.23H.sub.14F.sub.6N.sub.2O.sub.4].sub.n 54.06 .+-. 0.10 2.73
.+-. 0.12 5.75 .+-. 0.13 (55.7)* (2.84)* (5.64)* TR-.beta.-PBO
membrane [C.sub.23H.sub.10F.sub.6N.sub.2O.sub.2].sub.n 60.33 .+-.
0.04 2.15 .+-. 0.08 6.01 .+-. 0.05 (60.0)* (2.19)* (6.09)* Comp.
HPI precursor membrane
[C.sub.23H.sub.10F.sub.6N.sub.2O.sub.6].sub.n 53.3 .+-. 0.04 1.91
.+-. 0.04 4.92 .+-. 0.02 Exam. 1 (54.8)* (1.84)* (5.11)*
TR-.alpha.-PBO membrane
[C.sub.23H.sub.10F.sub.6N.sub.2O.sub.2].sub.n 60.52 .+-. 0.05 2.05
.+-. 0.06 6.14 .+-. 0.07 (60.0)* (2.19)* (6.09)* *Theoretical
values
Experimental Example 4
Differential Scanning Calorimetry (DSC) Analysis
[0118] The PHA precursor membrane and the TR-.beta.-PBO membrane of
Example 1 and the HPI precursor membrane and the TR-.alpha.-PBO
membrane of Comparative Example 1 were subjected to DSC analysis to
measure glass transition temperatures (Tg) thereof. The DSC
analysis was carried out using a DSC-2010 TA Instruments system at
a heating rate of 20.degree. C./min under an N.sub.2 atmosphere.
The results thus obtained are shown in FIG. 3.
[0119] FIG. 3 is DSC thermograms of PHA precursor membrane and
TR-.beta.-PBO membrane Example 1 and the HPI precursor membrane and
TR-.alpha.-PBO membrane of Comparative Example 1.
[0120] As can be seen from FIG. 3, Tg of the PHA precursor membrane
and the TR-.beta.-PBO membrane were observed at 281.degree. C. and
377.degree. C., respectively. This behavior is attributed to the
rigid rod structure of benzoxazole. In addition, Tg of the HPI
precursor membrane was observed at 353.degree. C. However, Tg of
TR-.alpha.-PBO membrane obtained therefrom cannot be measured.
[0121] These results indicated that TR-.beta.-PBO membrane chains
are softer and more flexible than TR-.alpha.-PBO membrane
chains.
Experimental Example 5
Analysis of Tensile Strength and Elongation
[0122] The tensile strength and elongation were measured for the
PHA precursor membrane and TR-.beta.-PBO membrane of Example 1 and
HPI precursor membrane and TR-.alpha.-PBO membrane of Comparative
Example 1. For measurement of the physical properties, five
specimens for respective membranes with a width of 0.5 cm, a length
of 4 cm and a thickness of 60-70 .mu.m were prepared. The physical
properties were characterized to study stress-strain behavior of
the polymer samples using an Autograph AGS-J (Shimadzu, Kyoto,
Japan). The results thus obtained are shown in Table 3 below:
TABLE-US-00003 TABLE 3 Tensile strength Elongation Type (MPa) (%)
Ex. 1 PHA precursor membrane 63 2.3 TR-.beta.-PBO precursor
membrane 87 6.0 Comp. HPI precursor membrane 62 2.7 Ex. 1
TR-.alpha.-PBO precursor membrane 69 3.4
[0123] As can be seen from Table 3 above, the polybenzoxazole
membrane shows increased tensile strength and elongation, as
compared to precursor membranes. In particular, the TR-.beta.-PBO
membrane according to Example 1 of the present invention has even
higher tensile strength and elongation than the TR-.alpha.-PBO
membrane of Comparative Example 1. This means that the membranes
prepared by the method according to the present invention are more
flexible and have higher strength.
Experimental Example 6
Wide Angle X-ray Diffraction Pattern Analysis
[0124] The PHA precursor membrane and the TR-.beta.-PBO membrane of
Example 1 and the HPI precursor membrane and the TR-.alpha.-PBO
membrane of Comparative Example 1 were subjected to wide-angle
X-ray diffraction (WAXD) analysis to confirm morphologies thereof.
The analysis was carried out using a wide angle X-ray
diffractometer (D/MAX-2500, Rigaku, Japan).
[0125] FIG. 4(a) is X-ray diffraction patterns of the HPI precursor
membrane and the TR-.alpha.-PBO membrane of Comparative Example 1.
FIG. 4(b) is X-ray diffraction patterns of the PHA precursor
membrane and the TR-.beta.-PBO membrane of Example 1.
[0126] As can be seen from FIG. 4, all of the membranes show broad
patterns, meaning that they have an amorphous structure. In
addition, after the thermal conversion from the HPI precursor
membrane to the TR-.alpha.-PBO membrane, the peak center (2.theta.)
shifts from 14.6 to 14.15 degrees, and after thermal conversion
from the PHA precursor membrane to the TR-.beta.-PBO membrane, the
peak center (2.theta.) shifts from 15.4 to 14.7 degrees.
Experimental Example 7
Measurement of Free Volume-Related Physical Properties
[0127] The physical properties were measured for the PHA precursor
membrane, TR-.beta.-PBO membrane of Example 1 and the HPI precursor
membrane and the TR-.alpha.-PBO membrane of Comparative Example 1.
The results thus obtained are shown in Table 4 below.
[0128] First, the density of the membranes was measured by a
buoyancy method using a Sartorius LA 120S analytical balance. The
fractional free volume (FFV, Vf) was calculated from the data in
accordance with Equation 1 below [W. M. Lee. Selection of barrier
materials from molecular structure. Polym Eng Sci. 1980, 20,
65-9].
FFV = V - 1.3 Vw V Equation 1 ##EQU00001##
[0129] wherein V is the polymer specific volume and V.sub.w is the
specific Van der Waals volume. The Van der Waals volume was
estimated by a Cerius 4.2 program using a synthia module based on
the work of J. Bicerano [J. Bicerano. Prediction of polymer
properties, Third Edition. Marcel Dekker Inc. 2002].
[0130] The d-spacing was calculated in accordance with Bragg's
equation from X-ray diffraction pattern results.
TABLE-US-00004 TABLE 4 V V.sub.wb Incre- D- Density (cm.sup.3/
(cm.sup.3/ V.sub.f ment in spacing Type (g/cm.sup.3) g) g) (FFV)
V.sub.f (%) (.ANG.) Ex. 1 PHA 1.450 0.690 0.462 0.129 5.75
precursor membrane TR-.beta.- 1.413 0.708 0.444 0.184 +43 6.02 PBO
membrane Comp. HPI 1.478 0.667 0.443 0.148 6.06 Ex. 1 precursor
membrane TR-.alpha.- 1.362 0.734 0.457 0.190 +28 6.25 PBO membrane
b: value measured with MS modeling software 4.0
[0131] As can be seen from Table 4, in the case of Comparative
Example 1, the density of the thermally converted TR-.alpha.-PBO
membrane was considerably lower than that of the HPI precursor
membrane due to the evolution of CO.sub.2 generated during thermal
conversion, and in the case of Example 1, the density of the
thermally converted TR-.beta.-PBO membrane was slightly lower than
that of the PHA precursor membrane due to dehydration during
thermal conversion.
[0132] Furthermore, V.sub.f of thermally converted PBOs is higher
than those of respective precursors due to thermal rearrangement in
a solid state. The TR-.beta.-PBO membrane shows a slightly lower
V.sub.f than the TR-.alpha.-PBO membrane, but there is no
significant difference in V.sub.f between the membranes.
[0133] As can be seen from Table 4, the d-spacing of the PHA
precursor membrane and the TR-.beta.-PBO membrane are substantially
lower than those of the HPI precursor membrane and TR-.alpha.-PBO
membrane. The decrease in d-spacing affects pores and free volume
elements, allowing permeation of smaller gas molecules.
Experimental Example 8
Molecular Dynamics (MD) Simulation of Gas Sorption
[0134] The PHA and HPI precursor membranes and PBO polymer membrane
were simulated using the computer program Materials Studio modeling
to confirm gas adsorption properties. The 4.2 COMPASS force field
(Condensed-phase Optimized Molecular Potentials for Atomistic
Simulation Studies) was used in all the simulations. Molecular
dynamics (MD) were calculated using the Amorphous Cell module of
the MS program. The O.sub.2 and N.sub.2 sorption amounts were also
calculated from a sorption module allowing simulation of absorption
of pure sorbate. Adsorption isotherms obtained from
constant-pressure simulations for O.sub.2 and N.sub.2 are shown in
FIG. 5.
[0135] FIG. 5(a) is adsorption isotherms of constant-pressure
simulations for O.sub.2. FIG. 5(b) is adsorption isotherms of
constant-pressure simulations for N.sub.2.
[0136] As can be seen from FIGS. 5(a) and 5(b), in the case of the
HPI and PHA precursor membranes, average O.sub.2 and N.sub.2
loading per cell was about 10 to 1,000 kPa due to their low
fractional free volume contents. In contrast, the PBO membrane
showed extremely high gas loadings around low fugacity region.
These results, obtained from molecular simulations, indicate that
the PBO separation membranes can sufficiently accumulate gas
molecules therein.
Experimental Example 9
Nitrogen Adsorption and Desorption Analysis
[0137] The PHA precursor membrane and the TR-.beta.-PBO membrane of
Example 1 and the HPI precursor membrane and the TR-.alpha.-PBO
membrane of Comparative Example 1 were subjected to N.sub.2
adsorption/desorption experiments. The BET adsorption isotherms for
N.sub.2 at 77K were determined using a Micrometrics ASAP 2020
surface area and porosity analyzer (Atlanta, USA). The adsorbents
were degassed at 200.degree. C. overnight before the adsorption
measurements. The specific surface areas, S.sub.BET, were
calculated from the linear form of the Brunauer-Emmett-Teller (BET)
equation.
[0138] FIG. 6 is N.sub.2 adsorption/desorption isotherms at
-196.degree. C. for the HPI precursor membrane (a) and the
TR-.alpha.-PBO membrane (b) of Comparative Example 1, and the PHA
precursor membrane (c) and the TR-.beta.-PBO membrane (d) of
Example 1.
[0139] As can be seen from FIG. 6, all the TR-.alpha.-PBO and
TR-.beta.-PBO membranes show a higher nitrogen volume than those of
their precursor membranes. This means that the thermally treated
PBO membranes have increased pore size, as compared to precursor
membranes.
[0140] As mentioned above, the TR-PBO membranes induced by the
precursors, HPI and PHA, have larger microcavities than those of
the precursors. In particular, as apparent from Tables 1 to 3 and
FIGS. 1 to 6, there are differences in properties between
TR-.beta.-PBO using PHA as the precursor and TR-.alpha.-PBO using
HPI as the precursor. Furthermore, the TR-.beta.-PBO membranes have
a lower d-spacing than the TR-.alpha.-PBO membranes, thus enabling
efficient separation of gas pair including small gases.
Experimental Example 10
Gas Permeability and Permselectivity Analysis
[0141] For the PHA precursor membrane and TR-.beta.-PBO membrane of
Example 1 and the HPI precursor membrane and the TR-.alpha.-PBO
membrane of Comparative Example 1, permeability and permselectivity
for various gases were measured.
[0142] The gas permeability was measured with high vacuum time-lag
equipment using single gases (1 bar, 25.degree. C.). Five samples
with a thickness 30 .mu.m for respective membranes were used. The
results thus obtained are shown in Table 5 below.
TABLE-US-00005 TABLE 5 Gas permeability Gas permeability O.sub.2
N.sub.2 CO.sub.2 H.sub.2 He CH.sub.4 (size) (Barrer.sup.a) (3.46
.ANG.) (3.64 .ANG.) (3.36 .ANG.) (2.89 .ANG.) (2.6 .ANG.) (3.80
.ANG.) Ex. 1 PHA precursor 1 0.2 4 15 24 0.1 membrane TR-.beta.-PBO
membrane 15 3 58 114 121 2 Comp. HPI precursor membrane 4 1 17 43
62 0.2 Ex. 1 TR-.alpha.-PBO membrane 148 34 952 635 421 23
(Barrer.sup.a): 10.sup.-10 (cm.sup.3(STP)cm/cm.sup.2scmHg)
TABLE-US-00006 TABLE 6 Gas selectivity O.sub.2/ H.sub.2/ CO.sub.2/
He/ H.sub.2/ CO.sub.2/ Type N.sub.2 N.sub.2 N.sub.2 N.sub.2
CH.sub.4 CH.sub.4 Ex. 1 PHA precursor 6 89 25 136 186 52 membrane
TR-.beta.-PBO membrane 5 39 20 42 58 30 Comp. HPI precursor
membrane 7 78 31 113 200 80 Ex. 1 TR-.alpha.-PBO membrane 4 19 28
13 27 41
[0143] As can be seen from Table 5 above, gas permeabilities of the
TR-.beta.-PBO and TR-.alpha.-PBO membranes were significantly
higher than those of the precursor membranes.
[0144] As apparent from Table 6, when H.sub.2/CH.sub.4,
H.sub.2/N.sub.2, He/N.sub.2 and O.sub.2/N.sub.2 are separated, in
terms of selectivity, the precursor membranes are superior to PBO
membranes, but the TR-.beta.-PBO membrane is still higher than
TR-.alpha.-PBO membrane.
[0145] Useful separation membranes must be selected, taking into
consideration the permeability and selectivity. In this regard, the
TR-.beta.-PBO membrane prepared according to the present invention
exhibits superior permeability and selectivity, and in particular
is more effective in separating small gases such as H.sub.2 and
He.
Experimental Example 11
Hydrogen Mix Gas Permeability Analysis
[0146] The hydrogen permeability and selectivity of the
TR-.beta.-PBO membrane according to the present invention and
conventional polymer separation membranes were measured at
30.degree. C. The results thus obtained are shown in Table 7
below:
TABLE-US-00007 TABLE 7 H.sub.2 permea- bility Selectivity Polymer
(Barrers.sup.b) H.sub.2/N.sub.2 H.sub.2/CH.sub.4 H.sub.2/CO.sub.2
H.sub.2/CO TR-.beta.-PBO 114 39 58 2 37 TR-.alpha.-PBO 635 19 27
0.7 12 Celluose acetate 3 12.5 12.4 0.4 -- Ethyl cellulose 87 27.2
4.6 3.3 -- Polybenzimidazole 0.09 -- -- 9 -- Polyetherimide 8 166
222.9 5.9 -- Polydimethylsiloxane 375 1.3 0.6 0.3 --
Polyimide(Matrimid) 28 87.8 112.4 2.6 -- Polymethylmetacrylate 2 2
4 4 -- Polymethylpentene 125 18.7 8.4 1.5 -- Polyphenyleneoxide 113
29.7 10.3 1.5 -- Polystyrene 24 39.7 29.8 2.3 12 Polysulfone 12
15.1 30.3 2 38 Polyvinyl acetate 15 11.6 16.8 1.2 --
(Barrer.sup.a): 10.sup.-10 (cm.sup.3(STP)cm/cm.sup.2scmHg)
[0147] As can be seen from Table 7, the TR-.beta.-PBO polymers
according to the present invention exhibit superior hydrogen
permeability and selectivity for gas pair, as compared to other
polymers, thus being useful for separation membranes.
Experimental Example 12
Analysis of Correlation Between Permeability and Selectivity
[0148] The H.sub.2 permeability and selectivity for H.sub.2/N.sub.2
and H.sub.2/CH.sub.4 of the TR-.beta.-PBO membrane according to the
present invention and conventional polymer membrane were measured.
The results thus obtained are shown in FIGS. 7(a) and 7(b).
[0149] FIG. 7(a) is a graph showing H.sub.2
permeability-H.sub.2/N.sub.2 selectivity of the TR-.beta.-PBO
membrane and conventional polymer membranes and FIG. 7(b) is a
graph showing H.sub.2 permeability-H.sub.2/CH.sub.4 selectivity of
the TR-.beta.-PBO membrane and conventional polymer membranes.
[0150] As can be seen from FIGS. 7(a) and 7(b), the TR-.beta.-PBO
membrane according to the present invention exhibits superior
permeability and selectivity, as compared to conventional polymer
membranes.
High Temperature Separation Performance of High Molecular Weight
Polybenzoxazoles
[0151] Materials. To prepare thermally rearranged polybenzoxazoles
for high temperature gas separation, PHA precursors were
synthesized from the reaction of bisaminophenol and three different
structures of diacid chlorides as shown in Scheme 5, where the
designated reference numbers will apply for this example
section.
##STR00033##
Scheme 5. Preparation of poly(o-hydroxyamide)s (PHAs) and thermally
rearranged polybenzoxazoles (TR-PBDs)
[0152] The 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane
(bisAPAF) (7) as a bisaminophenol was purchased from Central Glass
Co. Ltd (Tokyo, Japan). Two rigid aromatic acid chlorides comprized
of meta-phenylene (isophthaloyl dichloride, IPCl, 9a) and
para-phenylene (terephthaloyl dichloride, TPCl, 9b) moieties from
Aldrich Chemical Co. (Milwaukee, Wis., USA) and one relatively
flexible acid chloride including hexafluoroisopropane domain
((4,4'-hexafluorois opropylidene bis(benzoyl chloride), 6FCl, 9c)
were designed to investigate the structure-property relationship of
the precursor PHAs as well as the effect of thermal treatment on
the physical properties of TR-PBDs. N-methyl-2-pyrrolidinone (NMP),
dimethylformamide (DMF), n-hexane and toluene as solvents, and
pyridine, chlorotrimethylsilane (CTMS) and
N,N-dimethylaminopyridine (DMAP) as catalysts were obtained from
Aldrich Chemical Co. (Milwaukee, Wis., USA) and used without
further purification. Thionyl chloride was purchased from Samchun
Pure Chemical Co. (Gyeonggi-do, Korea).
[0153] As depicted in Scheme 5, three different di(acid chloride)
monomers (7) were reacted with equimolar diamine in
bis(aminophenol) (9) in the presence of pyridine as a Lewis base to
minimize the effect of byproduct of HCl. The exothermic reactions
were kept at a reduced temperature to avoid gelation of the polymer
solutions, followed by precipitation, filtration and drying. As a
catalyst, CTMS had a substantial role to activate the amine group
in bis(aminophenol) as well as to protect the hydroxide group, so
that high molecular weight polymers could be attained.
Consequently, as shown in Table 8 the precursor polymers showed the
average molecular weights (Mw) and intrinsic viscosities (ii)
exceeding 150,000 g/mole and 0.77 dL/g, respectively.
TABLE-US-00008 TABLE 8 Physical and thermal properties of PHAs
Polymer Molecular weight Viscosity (dL/g) Structure M.sub.n M.sub.w
M.sub.w/M.sub.n Inherent Intrinsic 3a 82,400 155,400 1.9 0.73 0.77
3b 36,500 189,400 5.2 0.82 0.79 3c 138,800 262,000 1.9 0.81
0.81
[0154] The molecular weight of 3c including bulky and rotational
moiety in both repeating units was the highest value of 262,000
g/mole as it was synthesized with small amount of DMAP. These PHAs
were characterized by 1H NMR spectra and FT-IR spectra in FIG. 8,
which indicated a broad absorption band at 3,400-3,100 cm.sup.-1
corresponding to amide and hydroxyl groups, a strong amide carbonyl
absorption (C.dbd.O) at 1,652 cm.sup.-1 and secondary amine
absorption (N--H) at 1,540 cm.sup.-1. The 1H NMR spectra of the
precursor also showed phenolic hydrogen at 10.3 ppm and 10.4 ppm
and amide group at 9.7 ppm and 9.8 ppm.
[0155] Monomers. High purity (99.9+%) bisAPAF (7) was dried
overnight in a vacuum oven at 120.degree. C. before use. Two
commercial monocyclic acid chlorides (9a, 9b) were recrystallized
under reduced pressure at 120.degree. C. and stored in an inert
atmosphere. To synthesize 6FCl (9c), 10 g (30 mmol) of
2,2-bis(4-carboxyphenyl)hexafluoropropane (6FOH) was treated with
25 ml of thionyl chloride in a three-neck round-bottomed flask
connected with a dean stark trap and a condenser, followed by
heating slowly to 90.degree. C. in an oil bath and stirring for
another 6 hours. The 6FCl solidified at reduced pressure and was
poured into hexane, filtered and recrystallized. The final 6FCl was
obtained as fine white powders after vacuum sublimation at
100.degree. C. This novel monomer structure was confirmed by FT-IR
spectra, which indicated a distinct peak at 1,780 cm.sup.-1
corresponding to carboxylic acid chloride without any residual peak
at 1,704 cm.sup.-1 from carboxylic acid.
[0156] Precursor polyhydroxylamides (PHAs). The synthesis of three
PHA precursors were performed by the same protocol except that
different acid chloride monomers were used. In a three-neck
round-bottomed flask, 3.66 g (10 mmol) of bisAPAF were dissolved in
20 ml of NMP under a nitrogen atmosphere, followed by dropping both
5.11 ml (40 mmol) of CTMS and 3.24 ml (40 mmol) of pyridine. After
the catalysts reacted with the bis(aminophenol) into a silylated
form, 10 mmol of each diacid chloride monomer was poured to the
solution and stirred vigorously in an ice bath for 4 hours,
resulting in a viscous and pale yellowish solution. For the bulky
monomer (9c), 4 mmol of DMAP was also added during the exothermic
reaction between diamine and diacid chlorides. After terminating
the reaction, the solution was precipitated in distilled water,
filtered repeatedly and dried at 100.degree. C. under vacuum.
[0157] PHA based on (bisAPAF-IPCl) (3a). 1H NMR (300 MHz,
DMSO-d.sub.6): 10.3 (OH), 9.7 (NH); FT-IR (powder): (--OH) at
3400-3100 cm.sup.-1, amide (C.dbd.O) at 1650 cm.sup.-1, (N--H) at
1530 cm.sup.-1; molecular weight: Mw=155,365, Mn=82,380; Tg (DSC):
211.degree. C.; density 1.45 g/cm.sup.3; fractional free volume
(FFV) 0.129.
[0158] PHA based on (bisAPAF-TPCl) (3b). 1H NMR (300 MHz,
DMSO-d.sub.6): 10.3 (OH), 9.7 (NH); FT-IR (powder): (--OH) at
3400-3100 cm.sup.-1, amide (C.dbd.O) at 1650 cm.sup.-1, (N--H) at
1530 cm.sup.-1; molecular weight: Mw=189,364, Mn=36.493; Tg (DSC):
261.degree. C.; density 1.46 g/cm.sup.3; fractional free volume
(FFV) 0.123.
[0159] PHA based on (bisAPAF-6FCl) (3c). 1H NMR (300 MHz,
DMSO-d.sub.6): 10.3 (OH), 9.8 (NH); FT-IR (powder): (--OH) at
3400-3100 cm.sup.-1, amide (C.dbd.O) at 1650 cm.sup.-1, (N--H) at
1530 cm.sup.-1; molecular weight: Mw=262,011, Mn=138,810; Tg (DSC):
258.degree. C.; density 1.40 g/cm.sup.3; fractional free volume
(FFV) 0.185.
[0160] Thermally rearranged polybenzoxazoles (TR-PBOs). PHA powders
were dissolved in NMP at 15 wt % concentration, and cast onto
well-cleaned glass plates using a doctor blade to control the
thickness of precursor films between 30-40 .mu.m. PHA solutions
were kept at 80.degree. C. overnight and then heated to 100, 150,
200 and 250.degree. C. in a vacuum oven. The resultant PHA films
washed in distilled water were cut to 5.times.5 cm.sup.2 size and
treated to 350.degree. C. at a heating rate of 5.degree. C./min in
a muffled furnace (Lenton, London, UK) so that each precursor (3)
can be converted into PBO (5) via intermediate (4) as described in
Scheme 1.
[0161] PBO based on bisAPAF-IPCl (5a). Tg (DSC): 303.degree. C.;
density 1.32 g/cm.sup.3; d-spacing: 0.672 nm; fractional free
volume (FFV) 0.238.
[0162] PBO based on bisAPAF-TPCl (5b). Tg (DSC): 375.degree. C.;
density 1.39 g/cm.sup.3; d-spacing: 0.614 nm; fractional free
volume (FFV) 0.198.
[0163] PBO based on bisAPAF-6FCl (5c). Tg (DSC): 326.degree. C.;
density 1.27 g/cm.sup.3; d-spacing: 0.606 nm; fractional free
volume (FFV) 0.282.
[0164] Characterizations. Polymer structures of PHAs and TR-PBOs
were confirmed by fourier-transformation infrared spectroscopy
(FT-IR) (Magna-IR 760 ESP spectroscopy, Thermo Fisher Scientific
Inc, Waltham, Mass.) and .sup.1H-NMR spectra (Varian Mercury Plus
300 MHz spectrometer, Varian, Inc, Palo Alto, Calif.). Elemental
analyses (EA) data were obtained by Thermofinnigan EA 1108 at
1000.degree. C. with WO.sub.3/Cu as a catalyst and BBOT
(2,5-bis(5-tert-butyl-benzoxazole-2-yl)thiophene) as a standard
material. Inherent viscosities of the precursor polymers were
measured by using Ubbelohde viscometer (Automatic dilution
viscosity measuring system, SI Analytics-Schott instruments,
Germany) at 27.degree. C. Molecular weights of precursor PHAs were
measured by gel permeation chromatography (Waters GPC system,
Milford, Mass.) with PLgel 10 uM Mixed-B LS 300 in 7.5 mm column
and Waters 2414 Refractive Index (R1) detector in NMP solution
including 0.05 M LiBr at 50.degree. C. on the basis of standard
poly(methyl methacrylate) (PMMA).
[0165] Conversion of TR-PBO were investigated by thermogravimetric
analysis (TGA) with mass spectroscopy (MS), (TGA Q500, TA
Instruments, New Castle, Del.) at a rate of 10.degree. C./min under
N.sub.2 with Thermo Star GSD 301T (Pfeiffer Vacuum GmbH, Asslar,
Germany) to confirm thermal stability of each PHA structure,
conversion temperature range with H.sub.2O removal and degradation
temperature. Differential scanning calorimetry (DSC, Q20, TA
Instruments, New Castle, Del.) was used for measurement of glass
transition temperature (Tg) in PHAs and TR-PBOs. Measurement
conditions were decided within the degradation temperatures by TGA,
at the rate of 5.degree. C./min under N.sub.2 from 180.degree. C.
to 300.degree. C. and 400.degree. C. for PHAs and TR-PBOs,
respectively. Mechanical properties were characterized to study
stress-strain behavior of the polymer samples by using Autograph
AGS-J (Shimadzu, Kyoto, Japan) with two film specimens of each
sample (11/4'' High ASTM D-638 Type). Wide angle X-ray Diffraction
(WAXD) was applied to investigate d-spacing of PHAs and TR-PBOs by
X-ray diffractometer (Rigaku Denki D/MAX-2500, Rigaku, Japan). The
threshold values in the 20 range of 5.degree.-80.degree. with a
scan rate of 5.degree. C./min by 1.54 .ANG. wavelength of Cu
K.alpha. radiation source was employed to get the average
intermolecular distance through the following Bragg's equation:
d = n .lamda. 2 sin .theta. ( 1 ) ##EQU00002##
where .lamda. is the X-ray wavelength and .theta. is the angle of
maximum intensity in the amorphous halo exhibited by the polymer.
Density was obtained to buoyancy method using Sartorious LA 120S
analytical balance in water at 27.degree. C. Van der Walls volumes
corresponding to each polymer structures were calculated by Bondi's
group contribution theory to obtain the fractional free volume
(FFV, Vf), which was calculated using the following equation:
V.sub.f=(V-1.3V.sub.w)/V (2)
where V is the polymer-specific volume and V.sub.w is the specific
Van der Waals volume.
[0166] PALS Experimental. PALS was used to investigate the pore
size and relative pore concentration within the PHAs and TR-PBOs.
The size of the free volume elements within the polymers can then
be related to the transport properties of the membranes. PALS
measurements were undertaken on an EG&G Ortec fast-fast
coincidence system using a vacuum cell equipped with a heat
controller. Long lifetimes were collected by setting the range of
the time-to-amplitude converter to 200 ns and removing the
coincident unit to increase count rates. Each file consisted of 106
integrated counts and a minimum of 5 files were collected for each
sample or at each temperature. The FWHM resolution of the
instrument was determined to be 240 ps when measured with
.sup.60Co.
[0167] The positron source was prepared with 50 .mu.Ci of .sup.22Na
which was dried onto 2.54 .mu.m thick Ti foil and required no
background subtraction. The TR membranes were stacked to 2 mm
thickness and placed on each side of the positron source. The
sample and source were then placed in the vacuum cell and brought
to 5.times.10.sup.-4 Pa. The samples were all initially measured at
room temperature (20.degree. C.) under vacuum. PALS was also
measured on sample 5c from 30 to 230.degree. C. at 20 or 30.degree.
C. intervals and then returned to 30.degree. C. to ensure there
were no permanent changes in the free volume due to the heating
regime.
[0168] The PALS data was deconvoluted using a four component fit
with LTv9 software by fixing the first lifetime (.tau..sub.1) to
0.125 ns due to annihilation of the para positronium (p-Ps) and
freeing the second lifetime (.tau..sub.2) to .about.0.4 ns due to
free annihilation. Therefore two ortho-positronium (o-Ps)
components (.tau..sub.3 and .tau..sub.4) were associated with the
bimodal porosity of the PHAs and TR-PBOs. The t.sub.3 shorter
lifetimes were converted to pore sizes using the Tao-Eldrup
semi-empirical formula. The longer lifetimes and the lifetimes at
high temperatures were calculated using the rectangular Tao-Eldrup
(RTE) model.
[0169] Gas permeation properties. Gas permeation properties of PHAs
and TR-PBOs were measured by both constant-volume method, so called
as `time-lag method`, at room temperature and constant-pressure
method at high temperature. Gas permeabilities and diffusivities
were determined at the steady-state pressure increments in-between
vacuum and 760 Torr over the membranes for six representative
permanent gases (e.g. He, H.sub.2, CO.sub.2, O.sub.2, N.sub.2, and
CH.sub.4) at 300K as follows:
P = p t ( VT 0 l P 0 TA .DELTA. P ) ( 3 ) ##EQU00003##
where P is the permeability represented in Barrer, dp/dt is the
rate of pressure rise under the steady state, V (cm.sup.3) is the
downstream volume, L (cm) is the membrane thickness, T (K) is the
measurement temperature, .DELTA.p (cmHg) is the pressure
difference, A (cm.sup.2) is the effective membrane area, and
P.sub.0 and T.sub.0 are the standard pressure and temperature,
respectively.
[0170] Temperature dependence of the polymers were investigated for
H.sub.2 and CO.sub.2 targeted to a specific application. Based on a
careful consideration on safety issues in a convection oven, the
membrane cell was connected to pre-heated gas chamber equipped with
several valves and manometers (Baratron 722 and 626A, MKS
instrument, MA, USA). Gas permeances were recorded at each
pressurized gas up to 20 bar at the temperature range of 300-493 K
and converted to gas permeabilities as follows:
P = Q .times. l A .times. .DELTA. P ( 4 ) ##EQU00004##
where Q (cm.sup.3/min) is the gas flow rate at downstream, l (cm)
is the membrane thickness, .DELTA.p is the pressure difference
(cmHg), and A (cm.sup.2) is the effective membrane area.
Permselectivity (.alpha..sub.1/2) is defined as the ratio of the
two gas permeabilities.
[0171] Thermal rearrangements. Thermal conversion of PHAs into
TR-PBOs occur by the attack of the hydroxide group into the
adjacent amide carbonyl group as thermal treatment accelerates
polymer chain mobility and reduces the activation energy for intra-
and inter-molecular reactions even at solid state. The intermediate
structures composed of fused five-membered rings undergo
dehydration to be conjugated with aromatic rings at around
350.degree. C. The intramolecular reactions were investigated
conveniently as tracing the weight change of PHAs and identifying
the evolved gases, which could be performed by mass spectroscopy
connected to thermogravimetric analysis.
[0172] As shown in FIGS. 9(a)-9(c), PHA precursor 3c has weight
reduction of around 6 wt % in the range of 240 to 380.degree. C.
Thermal conversion and decomposition of 3a and 3b possessing the
same chemical composition but different main chain formation of the
phenyl rings displayed the same trend, however, 3c which includes
hexafluoroisopropylidene group, C(CF.sub.3).sub.2, has the highest
initial conversion temperature (T.sub.ci). Note that the weight
drops coincide with the intensity variation of H.sub.2O at the same
temperature range without detection on other mass numbers in mass
spectroscopy. As a result, the thermally treated polymers were
confirmed by the newly detected FT-IR peaks (FIG. 10) at 1,054
cm.sup.-1 (C-0 stretching) and 1,475 cm.sup.-1 (C.dbd.N stretching)
in benzoxazole ring, as well as the peak disappearances at
3,400-3,100 and 1,650 cm.sup.-1 corresponding to hydroxyl groups
and amide carbonyl, respectively. The elemental analyses of PHAs
and TR-PBOs in Table 9 generally agreed well with the calculated
values for the proposed structures.
TABLE-US-00009 TABLE 9 Molecular Polymer formula of H N Total
structure repeating unit C (wt %) (wt %) (wt %) (wt %) PHA 3a
C.sub.23H.sub.14N.sub.2O.sub.4F.sub.6 59.83 2.60 6.49 68.92
(55.65)* (2.85)* (5.65)* (64.15)* 3b
C.sub.23H.sub.14N.sub.2O.sub.4F.sub.6 58.29 3.08 6.54 67.91
(55.65)* (2.85)* (5.65)* (64.15)* 3c
C.sub.32H.sub.18N.sub.2O.sub.4F.sub.12 55.79 2.83 4.78 63.4
(53.19)* (2.52)* (3.88)* (59.59)* *calculated values
[0173] Without intending to be bound by a particular theory,
hydroxyl groups in PHA are more flexible around the aromatic amide
linkage including secondary amine than those in HPI composed of
tertiary amine, thus PHAs can be thermally rearranged at
temperatures 100.degree. C. lower than HPIs. Moreover, differences
in the main chain and the following conversion routes can bring out
physical properties in the polymer matrix.
[0174] Physical properties of TR-polymers. The most significant
effect in the thermal rearrangement of these polymers is the change
of the physical properties such as intermolecular distance,
internal surface area, and fractional free volume (FFV) while the
changes in chemical structures contribute to the variation of glass
transition temperatures (Tg) and thermal degradation temperatures
(Td). In the case of TR-.alpha.-PBOs, their free volume increments
were almost doubled so that the FFV could reach to 30% or more.
Here, TR-.beta.-PBOs (5a-5c) obtained by thermal treatment at
350.degree. C. exhibited increased free volume compared to PHAs,
but were different from those of TR-.alpha.-PBOs. Referring to
FIGS. 12(a) and 12(b), the d-spacing values calculated by the
average two theta values from the WAXD patterns were enlarged with
increasing thermal treatment temperature. Apart from polymers
including bulky and rotational polar C(CF.sub.3).sub.2 groups which
have several strong crystalline peaks, PHA and PBO linked to
para-phenylene (3b to 5b) have larger intermolecular distances
compared to meta-phenylene polymers (3a to 5a).
[0175] Polymer densities and the resulting free volume calculations
showed a good correlation with the trend in d-spacing values. As
described in Table 10, the densities of PHAs were 1.4 gcm.sup.-1
(3c) to 1.46 gcm.sup.-1 (3b) according to their main chain
components and stiffness like those of conventional aromatic
polymers.
TABLE-US-00010 TABLE 10 Tem- d- V.sub.w perature 2theta spacing
Density V (cm.sup.3/ FFV Polymers (.degree. C.) (degree) (nm)
(g/cm.sup.3) (cm.sup.3/g) g) (--) 3a 250 13.88 0.630 1.45 0.690
0.462 0.129 4a 300 13.65 0.648 1.45 0.690 0.445 0.161 5a 350 13.2
0.672 1.32 0.758 0.444 0.238 3b 250 14.25 0.590 1.46 0.685 0.462
0.123 4b 300 14.55 0.610 1.43 0.699 0.445 0.172 5b 350 14.40 0.614
1.39 0.719 0.444 0.198 3c 250 15.50 0.583 1.40 0.714 0.448 0.185 4c
300 14.99 0.606 1.33 0.752 0.436 0.246 5c 350 15.35 0.606 1.27
0.787 0.435 0.282
[0176] As thermal treatment provides enough activation energy for
chain distortion and conversion, polymer densities diminished 5-10%
in TR.beta.-PBOs. The para-linked TR-.beta.-PBO (5b) retained the
highest density of 1.39 gcm.sup.-1 owing to the pristine packed
morphology at the same thermal treatment protocol whereas the bulky
sample (5c) showed a significant density drop (9.3%) as well as
density itself (1.27 gcm.sup.-1), because these polymers have small
thermal shrinkages less than 4%. Fractional free volume (FFV)
changes are also notable in that the improved values are not
anticipated for thermostable aromatic polymers. In the FFV
calculation, the samples (4) (Scheme 5) treated at 300.degree. C.
were considered discretionarily to exist in the state of
intermediate structures, where van der Walls volumes were close to
those of TR-.beta.-PBOs, although it was difficult to detect in the
reaction. FFVs increased generally in order of
250(3)<300(4)<350(5) and para-phenylene (b)<meta-phenylene
(a)<hexafluoroisopropylidene (c) for treatment temperatures and
structures, respectively. Although the FFVs were smaller than those
of TR-.alpha.-PBOs (0.28-0.35), they are comparative to FFVs of
amorphous fluoropolymers such as Hyflon AD series and Cytop.TM. as
well as polymers with intrinsic microporosity (PIMs), which are
promising polymers for separation and storages with FFVs of
0.19-0.33. High free volumes in those polymer matrixes contribute
to high sorption capability in their internal surfaces as well as
provide diffusion pathways for fast transport through the
polymers.
[0177] Positron annihilation lifetime spectroscopy (PALS) confirmed
these important characteristics by visualizing the free volume
elements as pore size distributions and intensities. As a positron
can live in the porous space with low electron density, the longer
lifetime of the positron, the larger the pore size in the material.
Computational software such as LTv9 and PAScual can exhibit several
individual lifetimes with their fit variances. As shown in FIGS.
11(a), 11(b), and 11(c) and Table 11, PHAs and TR-.beta.-PBOs have
bimodal distributions as other high free volume polymers (e.g.
PTMSP, PIM, TR-.alpha.-PBOs) have shown.
TABLE-US-00011 TABLE 11 Treatment Cavity Cavity Temperature
Diameter Intensity, I.sub.3 Diameter Intensity, I.sub.4 Polymers
(.degree. C.) .tau..sub.3 (ns) (nm) (%) .tau..sub.4 (ns) (nm) (%)
3a 250 0.82 .+-. 0.13 0.27 .+-. 0.06 11.09 .+-. 4.12 2.51 .+-. 0.03
0.655 .+-. 0.004 18.57 .+-. 0.45 4a 300 0.90 .+-. 0.10 0.30 .+-.
0.04 9.93 .+-. 1.99 2.92 .+-. 0.03 0.716 .+-. 0.004 21.97 .+-. 0.37
5a 350 0.99 .+-. 0.09 0.33 .+-. 0.03 8.44 .+-. 1.05 3.03 .+-. 0.03
0.731 .+-. 0.004 19.14 .+-. 0.48 3b 250 1.01 .+-. 0.11 0.34 .+-.
0.04 8.07 .+-. 0.77 2.92 .+-. 0.04 0.716 .+-. 0.006 16.09 .+-. 0.51
4b 300 0.96 .+-. 0.11 0.32 .+-. 0.04 8.68 .+-. 0.90 3.13 .+-. 0.03
0.744 .+-. 0.004 19.51 .+-. 0.44 5b 350 0.96 .+-. 0.06 0.32 .+-.
0.02 9.68 .+-. 0.72 3.31 .+-. 0.03 0.767 .+-. 0.004 21.00 .+-. 0.33
3c 250 0.85 .+-. 0.08 0.28 .+-. 0.03 9.10 .+-. 1.34 2.80 .+-. 0.02
0.699 .+-. 0.003 17.49 .+-. 0.22 4c 300 1.22 .+-. 0.21 0.40 .+-.
0.06 7.09 .+-. 0.49 3.60 .+-. 0.05 0.802 .+-. 0.006 22.16 .+-. 1.00
5c 350 1.24 .+-. 0.10 0.40 .+-. 0.03 8.88 .+-. 0.54 3.79 .+-. 0.03
0.825 .+-. 0.004 21.54 .+-. 0.76
[0178] Lifetime of PHAs, which have 0.82-1.01 ns and 2.50-2.92 ns
for .tau..sub.3 and .tau..sub.4, respectively, ascended to
0.96-1.24 ns and 3.03-3.79 ns in TR-.beta.-PBOs, corresponding to
the cavity size of 0.32-0.4 nm and 0.73-0.83 nm, generally in the
order of 3a<3c<3b<5a<5b<5c. The significant changes
in both smaller and larger cavities indicates that the chain
rearrangement enlarged the internal free volumes within the polymer
matrix. Therefore, the increased free volume elements evolved by
thermal rearrangement of HPAs are expected to have superior
transport properties to small gas and vapor molecules. Despite the
two cavities sizes being comparable to those of TR-.alpha.-PBOs
(0.38 and 0.9 nm), they were slightly smaller, therefore, it would
be predicted that their diffusion selectivity for small gas
penetrants would be improved although diffusion through the
polymers could be restricted to the high free volume polymers.
[0179] Gas separation properties. As transport of gas molecules
through polymers were governed by well-known `solution-diffusion`
mechanism, TR-PBOs retaining high free volume elements, as
elucidated by X-ray diffraction, density, FFV and PALS, exhibited
superior permeabilities for small gas molecules compared to
conventional glassy polymers. As can be seen in Table 12, gas
permeabilities of PHAs (3a-3c) showed relatively low gas
permeabilities and reasonably high ideal selectivities.
TABLE-US-00012 TABLE 12 Gas permeation properties of PHAs and
TR-.beta.-PBOs at 300 K Polymer Gas permeability Ideal selectivity
Structures He H.sub.2 CO.sub.2 O.sub.2 N.sub.2 CH.sub.4
O.sub.2/N.sub.2 CO.sub.2/N.sub.2 CO.sub.2/CH.sub.4 H.sub.2/CO.sub.2
H.sub.2/CH.sub.4 N.sub.2/CH.sub.2 3a 9.2 5.4 2.1 0.47 0.09 0.03 5.2
23 69 2.6 180 3.0 3b 20 14 4.7 1.4 0.2 0.1 6.3 21 43 3.0 128 2.1 3c
106 75 32 8.0 1.6 0.83 5.1 20 40 2.3 93 2.0 5a 70 60 23 5.7 1.0 0.5
5.6 23 45 2.6 115 2.0 5b 82 85 53 11 2.3 1.4 4.9 23 39 1.6 59 1.6
5c 251 255 199 45 11 6.4 4.2 18 31 1.3 40 1.7 Pressure: 760 Torr.
Temperature: 300 K
[0180] H.sub.2 permeability of 3b membrane exhibited 14 Barrer
while ideal selectivity of hydrogen over carbon dioxide is about 3.
On the other hand, 3b was treated at 350.degree. C. to become
TR-.beta.-PBO membrane (5b), H.sub.2 permeability was improved 6
times while selectivity was reduced in half. This result is
consistent with an increase in free volume as the larger gases
(kinetic diameter>3.2 .ANG.), which are originally subject to
larger energy barriers due to size exclusion within 3b, achieve
enhanced diffusivities within 5b as almost barrier-free pathways
are presented. Smaller gases (kinetic diameter<3.2 .ANG.) on the
other hand, achieve enhanced solubilities at a detriment to
diffusivity where an increase in free volume creates ideal
pore-filling space. Therefore, permselectivities for small gas
pairs were partially mitigated. Notice that H.sub.2 permeability of
5a was about 60 Barrer and selectivity of H.sub.2/CO.sub.2 was
still about 2.6. In 5a and 5b, as evidenced in Table 10 and FIGS.
11(a)-(c), the difference in their size exclusion capabilities
resulted in higher permselectivities in the former although they
showed similar He permeability. 5c membranes showed relatively high
permeabilities for six representative gases among the TR membranes
tested because of the high free volume and large cavity sizes. For
this membrane, CO.sub.2 permeability was about 200 Barrer and the
selectivity over nitrogen and methane was about 18 and 31,
respectively. As shown in FIGS. 13(a)-(c), there was a trade-off
relationship between gas permeability and permselectivity, the
separation performances approached but did not surpass the
Robeson's upper bounds. See [L. M. Robeson, Correlation of
separation factor versus permeability for polymeric membranes, J.
Membr. Sci., 1991, 62, 165; L. M. Robeson, The upper bound
revisited, J. Membr. Sci., 2008, 320, 390].
[0181] Temperature dependences on physical properties and
separation performances. Though aromatic polymers usually possess
glass transition temperatures greater than 150.degree. C., the
ability to utilize them at elevated temperatures has typically been
restricted because of the long-term stability and performance
reduction. While common glassy polymers have typically shown two
different rates of increasing free volume at the boundary of glass
transition temperature (Tg), high free volume polymers represent
very ambiguous behaviors in their patterns. Even though these
polymers have very high Tg, their cavity sizes in bimodal
distributions as well as unimodal distributions have a threshold at
a certain temperature under Tg and start to decline: for instance,
AF 2400 and PIMs showed thresholds at 170.degree. C. and
90-110.degree. C., respectively. The same phenomena were detected
in TR-PBOs. FIGS. 14(a) and (b) represent the changes of cavity
diameters of 5c membranes in terms of .tau..sub.3 and .tau..sub.4
as a function of temperature ranging from 30 to 220.degree. C.
measured using PALS. Noticeably, T.sub.3, representing the small
cavity, as well as .tau..sub.4, showing the large cavity, increase
as a function of temperature. However, .tau..sub.4 decreases at
temperatures above 200.degree. C. for the 5c membrane.
[0182] FIG. 15 (a) shows the permeability and selectivity variation
of H.sub.2 and CO.sub.2 for TR-.beta.-PBO membranes (5a-5c) as a
function of temperature from 30 to 230.degree. C. For the 5c
membrane, gas permeability of hydrogen and carbon dioxide was
tested at Los Alamos National Laboratory to confirm the accuracy of
the gas permeability measured in our laboratory. The results are
very consistent when using the same membranes measured at
temperatures up to 230.degree. C. In general, permeabilities of
H.sub.2 and CO.sub.2 both increase with temperature for all three
membranes. An increase in permeability of gases is understandable
from the view point of the changes in cavity size as a function of
temperature as was discussed in connection with FIG. 14. Note that
the increase of H.sub.2 permeability is pronounced in comparison to
that of CO.sub.2 resulting in the increase of selectivity of
H.sub.2/CO.sub.2 because the reduction of CO.sub.2 solubility at
higher temperatures are more critical than those of H.sub.2 and
thus counterbalance the higher diffusion increase of CO.sub.2.
Activation energies of H.sub.2 and CO.sub.2 derived from the
Arrhenius plot data such as FIG. 15(a) are 10.6, 6.3 kJ/molK in 5a,
and 7.8, 2.5 kJ/molK in 5c, respectively. In general the activation
energies are in the order of H.sub.2 (5a)>H.sub.2
(5b)>H.sub.2 (5c)>CO.sub.2 (5a)>CO.sub.2 (5c)>CO.sub.2
(5b) because gas molecules passing through smaller cavities are
easily disturbed for permeation and thus the temperature dependence
on permeation are more significant. As a result, 5a showed the
highest separation performance with 205.8 Barrer of H.sub.2
permeability and 6.2 of H.sub.2/CO.sub.2 selectivity at 215.degree.
C.
[0183] Therefore, H.sub.2/CO.sub.2 separation performances are
surprisingly improved in both permeability and selectivity at
elevated temperatures which is unique to other gas separations.
This peculiar temperature dependence of gas permeation has already
been noticed by Dye et al. Thermal energy prompts the increases in
diffusivity and thus the permeability of most gases for
TR-.beta.-PBO membranes, contributing to the exceeding upper bound
as can be seen in FIG. 15(b). Here, TR-.beta.-PBOs showed better
separation performances than TR-PBI reported in Han et al., J.
Membrane Sci., Vol. 357, 2010, pp. 143-151. Although there needs to
be further optimization and improvement in terms of selectivity for
TR-.beta.-PBO membranes, this result shows the potential for
TR-.beta.-PBO membranes for the syn gas separation application. The
data from FIGS. 15(a) and 15(b) is listed in the following Tables
13 to 16.
TABLE-US-00013 TABLE 13 TR-PBI T (.degree. C.) 1000/K He H2 CO2 O2
N2 CH4 CO .alpha. (H2/CO2) Permeability 30.00 3.30 868.44 1778.83
1624.09 336.64 61.93 35.26 93.60 1.10 60.00 3.00 905.92 1757.48
1598.92 327.05 76.79 54.08 119.66 1.1 90.00 2.75 907.26 1615.55
1267.72 289.49 82.04 70.58 129.44 1.27 120.00 2.54 893.61 1551.69
1004.15 262.58 85.28 81.43 133.40 1.55 Diffusivity 30.00 3.30
1.13E-06 1.12E-06 2.98E-07 7.48E-07 8.2E-07 4.11E-08 4.82E-07 3.76
60.00 3.00 1.01E-06 8.62E-07 4.47E-07 1.06E-06 9.78E-07 1.02E-07
5.12E-07 1.92 90.00 2.75 9.99E-07 1.05E-06 5.21E-07 8.22E-07
1.52E-06 2.13E-07 1.67E-06 2.02 120.00 2.54 1.1E-06 1.01E-06
6.33E-07 7.17E-07 2.19E-06 3.22E-07 2.23E-06 1.59 Solubility 30.00
3.30 0.0772 0.1586 0.5453 0.0450 0.0076 0.0858 0.0194 0.29 60.00
3.00 0.0896 0.2039 0.3573 0.0310 0.0079 0.0529 0.0234 0.57 90.00
2.75 0.0908 0.1535 0.2433 0.0352 0.0054 0.0332 0.0078 0.63 120.00
2.54 0.0814 0.1536 0.1585 0.0366 0.0039 0.0253 0.0060 0.97
TABLE-US-00014 TABLE 14 TR-b-PBO 6F-IP (5a) .degree. C. 1000/K H2
CO2 .alpha. (H2/CO2) Permeability 30 3.30 44 6 8 60 3.00 61 17 3.67
90 2.75 83 22 3.75 120 2.54 111 22 5 150 2.36 139 28 5 180 2.21 178
28 6.4 200 2.11 195 33 5.83 210 2.07 206 33 6.17 225 2.01 222 39
5.71
TABLE-US-00015 TABLE 15 6F-TP (5b) .degree. C. 1000/K H2 CO2
.alpha. (H2/CO2) Permeability 30 3.30 191 60 3.16 60 3.00 130 60
2.16 90 2.75 143 60 2.37 120 2.54 168 64 2.65 150 2.36 200 67 3 180
2.21 238 70 3.41 200 2.11 270 76 3.54 210 2.07 280 76 3.67 225 2.01
305 79 3.84
TABLE-US-00016 TABLE 16 6F-6F (5c) .degree. C. 1000/K H2 CO2
.alpha. (H2/CO2) Permeability 30 3.30 144 95 1.5 60 3.00 210 124
1.69 90 2.75 248 130 1.9 120 2.54 321 130 2.46 150 2.36 372 133
2.79 180 2.21 426 140 3.05 200 2.11 451 146 3.09 210 2.07 464 156
2.98 225 2.01 499 149 3.34
[0184] As apparent from the foregoing, the benzoxazole-based
polymers according to the present invention are suitable for use in
various separation membranes, in particular, separation membranes
applicable to small gases. The stability of these membrane
materials at high temperatures makes them suitable for various gas
separation applications at temperatures higher than most current
commercially available polymeric membranes. In many gas separations
applications using conventional polymeric membrane materials, the
feed gas to the membrane must be cooled, because of
temperature/stability limitations of most current polymer membrane
materials. Such cooling is not required as a result of the present
invention.
[0185] For example, for separations of air (involving principally
separation of O.sub.2 from N.sub.2), the elevated pressure gas from
a compressor output is very hot, possibly at temperatures as high
as 100 to 200C, depending on the type of compressor. In air
separations used to enrich N.sub.2 by onboard inert gas generation
systems (commonly referred to as OBIGGS), the feed air to the
membrane is obtained from a compression stage of a turbine (in an
aircraft engine), where temperature of the gas can be as high as
about 200 C. Using conventional polymeric membrane materials, which
cannot tolerate such high temperatures, a heat exchanger must be
used to first cool the feed gas to the membrane. Need for such
after-cooling could be largely avoided for the membrane polymers of
the present invention, since these polymers show much better high
temperature stability. For example, as shown by the TGA curves in
FIGS. 1 and 9, decomposition of the polymer does not begin to occur
until temperatures exceed approximately 400 to 500.degree. C. Hot
operating environments may also be encountered, where the polymers
of the present invention may be useful by virtue of their stability
at high temperature, such as under the hood in the engine
compartments of diesel engines. For diesel engines, it may be
desirable to use a membrane to remove some of the O.sub.2 from feed
air, so as to reduce the nitrogen oxides (NOx), which are harmful
pollutants normally contained in the exhaust gases from diesel
engines operating on normal air.
[0186] Further, many H.sub.2 separations are employed in a variety
of chemical processing and refinery process applications, such as
separations of H.sub.2 from CH.sub.4 and other light hydrocarbons,
H.sub.2 from CO, H.sub.2 from N.sub.2, and the like. Many of these
process gas streams operate at very high temperatures, such that
use of convention polymer membrane materials requires that the feed
gas to the membranes must be cooled prior to the gas contacting the
membrane. In refining processes, for example to name just a few of
many, hydro-treating processes may operate at temperatures ranging
from about 200.degree. C. to over 400.degree. C., isomerization
processes may operate in the range of about 150.degree. C. to about
200.degree. C., catalytic reforming processes may operate at even
higher temperatures, for example, in the vicinity of
400-500.degree. C. These are just a few of many examples of
potential uses of the polymers of the present invention, which are
made possible by their high temperature stability.
* * * * *