Polymer Membranes for Gas and Vapor Separation - American

Chapter 19

Gas Separation Properties of Modified Poly(ether ketone[sulfone]) with Phthalic Side Group Role of Pendent Groups and Physical Cross-Linking on Gas Permeation Properties of Polymers Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 23, 2016 | http://pubs.acs.org Publication Date: September 2, 1999 | doi: 10.1021/bk-1999-0733.ch019

Jiping Xu, Zhonggang Wang, and Tianlu Chen Changchun Institute of Applied Chemistry, CAS, 159 People's Street, Changchun, 130022 Peoples Repubic of China

Phenolphthalein based polyetherketone and polyethersulfone (PEK-C & PES-C) were modified to improve their gas permeation properties. The influence of side groups on gas permeation properties was studied by using dimethylphenolphthalein (DMPPH), tetramethylphenolphthalein (TMPPH) and diisopropyidimethyl-phenolphthalein (DIDMPPH) to synthesize a systematic series of polymers. The dimethyl substituted polymers show lower gas permeabilities than unsubstituted ones, while the T M - and DIDM- polymers give enhanced permeabilities. In some cases, simultaneous increases of both permeability and permselectivity were observed. The reasons were discussed in terms of free volume. The lactone ring of the pendent phthalic group of phenolphthalein and its derivatives was opened by reduction to the corresponding phenolphthalin(PPL)s and their polyetherketone(sulfone) analogs were synthesized. Introduction of pendent carboxylic groups greatly enhanced the permeability and/or permselectivity. Ionomers obtained from salt formation of the PPL polymers show very high gas permselectivity.

The Chinese patented polyetherketone and polyethersulfone (PEK-C & PES-C) are amorphous polymers with high glass transition temperatures (T =228°Cand 260°C respectively)(1-3). They were synthesized by nucleophilic polycondensation of phenolphthalein (PPH) and dichlorobenzophenone or dichlorodiphenylsulfone in sulfolane in the presence of potassium carbonate. They were found to be good membrane materials for ultrafiltration and microfiltration(4) and could also be used as charged membranes (after sulfonation or chloromethylation/quaternization) for nanofiltration and electrodialysis processes. However, the gas separation properties of these materials are moderate, similar to those of polysulfone. In order to further improve their gas permeation properties, g

© 1999 American Chemical Society

Freeman and Pinnau; Polymer Membranes for Gas and Vapor Separation ACS Symposium Series; American Chemical Society: Washington, DC, 1999.

269

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270 modification of the pendent phthalic group was studied: the side lactone ring was transformed into a lactam ring in order to introduce hydrogen bonding between polymer chains. Membranes from PEK-H and PES-Η (having chemical structures similar to PEK-C and PES-C with the -0- in lactone ring of the phthalic group changed to -NH- or -NR-) and their copolymers show enhanced permselectivitiesf^. However, ammoniation of PPH under pressure has limited their practical application. From numerous studies of structure/gas permeation property relationships in polymers, two general conclusions can be reached: introduction of side alkyl groups to the aromatic ring usually increases the free volume of the polymer and hence enhances gas permeability while selectivity is lowered; and cross-linking of the polymer material by covalent bonds and also by hydrogen bonding or ionic bonds can increase permselectivity greatly. These principles were exploited in this work. First, dimethylphenolphthalein (DMPPH), tetramethylphenolphthalein (TMPPH) and diisopropyl-dimethylphenolphthalein (DIDMPPH) were used to synthesize the corresponding polymers: DMPEK-C, TMPEK-C, DIDMPEK-C, DMPES-C, TMPESC and DIDMPES-C, and their gas permeation properties were studied. Interestingly, the DM-substituted polymers show lower gas permeabilities than unsubstituted ones, while the T M - and DIDM- polymers give enhanced permeabilities. This can be explained based on the free volume concept. In some cases, simultaneous increases of both permeability and permselectivity were observed. Second, the lactone rings of the pendent phthalic groups of phenolphthalein and its derivatives were reduced via ring opening to the corresponding phenolphthalin(PPL)s, and their polyetherketone(sulfone)s were synthesized. Introduction of pendent carboxylic groups greatly enhanced permeability and/or permselectivity. Ionomers obtained from salt formation of the PPL polymers show very high gas permselectivity: around 300 for hydrogen/nitrogen, >11 for oxygen/nitrogen and 276,000 for water vapor/nitrogen. P E K - C and PES-C Derivatives with Side Subsituent Groups Based on preliminary experiments, the polymer from dimethylphenolphthalein and dichlorodiphenylsulfone (DMPES-C) has lower permeability to gases than PES-C, (which is in contradiction with common rules). Similar results have been observed for polysulfone and dimethylpolysulfone^. Hence, a series of substituted polymers were prepared for a systematic study of the role of substituent groups. Monomers. DMPPH was obtained from Beijing Reagents Co., TMPPH and DIDMPPH were obtained from Fluka, 4,4 -difluoro-diphenylsulfone(DFDPS) was obtained from Aldrich, 4,4'-dichlorodiphenylsulfone (DCDPS) was obtained from Shanghai Reagents Corp., and 4,4'-dinitrobenzophenone (DNBP) was synthesized in this laboratory(7,8,9). ,

Polymers. The following polymers were prepared by solution polycondensation of bisphenol, potassium carbonate and DFDPS, DNBP or DCDPS in DMSO or sulfolane. Structures were characterized by N M R (Unity-400) and FT-IR (Digilab FTS-20E).


271


Membranes. Dense membranes of the polymers were cast onto glass plates from 7% solution in CHCI3/CH2CICHCI2 (4:6 vol.), dried 24 h at room temp., then dried for 6 h at 60 °C, lifted from the glass plate in water, dried at 100°C for 4 h and finally dried for one week in a vacuum oven at 10 torr and 120°C. For polymers insoluble in the mixed solvent, membranes were cast from 7% DMF solution.

Polymer PEK-C DMPEK-C

Rl H H

R2 H H

R

3

H CH3

X

R4 H CH3

c=o c=o

CH

c=o

TMPEK-C

CH3

CH3

CH

DIDMPEK-C

CH3

CH3

H

H

CH(CH )2 H

c=o

PES-C

CH(CH )2 H

DMPES-C

H

H

CH

3

CH3

S02

TMPES-C

CH3

CH3

CH

3

CH3

S02

DIDMPES-C

CH3

CH3

CH(CH )2

3

3

3

3

S02

S02

CH(CH )2 3

3

Gas permeability coefficients for CO2, H2, O2, N2 and CH4 were measured by a vacuum manometric method with an upstream pressure of 5 atm. in the temperature range from 30 to 100°C The gas permeation data of the PEK series of polymers are summarized in Table I, and those for the PES series are recorded in Table II.

Table I. Polymer PEK-C DMPEK-C TMPEK-C DIDMPEK-C Ρ in barrers.

Gas permeation properties of polyetherketones at 30°C PH

2

11.7 10.3 21.5 42.5

α H /N 2

75.6 95.2 114.4 45.3

2

Po

2

0.95 0.87 1.55 4.85

α o /N 2

6.2 8.9 8.2 5.2

2

Pco

2

2.73 2.60 5.44 19.3

α co /CH 33.2 37.1 32.0 17.7


2

4

272 Table II.


Polymer PES-C DMPES-C TMPES-C DIDMPES-C Ρ in barrers.

Gas permeation properties of polyethersulfones at 30°C PH

α H /N

2

2

12.1 10.8 16.9 30.6

72.6 98.1 84.1 43.8

2

Po

2

0.95 0.87 1.55 4.85

α o /N 6.2 7.6 7.5 5.5 2

2

Pco

α CO /CH

5.74 3.12 7.69 19.4

40.1 42.9 34.2 20.9

2

2

4

Based on the data in Tables I and II, the gas permeability coefficients of the DM-based polymers is the lowest, similar to the results observed by Moe et a\,(6). The introduction of two methyl groups to the repeat unit of PEK(S)-C decreased permeability and increased permselectivity. Introduction of four methyl groups or two methyl and two isopropyl groups enhances the permeability. These results can be explained using the free volume concept. We suppose the bulky phthalic pendent group of PEK(S)-C provides some free volume to the polymer. The two methyl groups introduced in DMPEK(S)-C fill up some fraction of the free volume produced by the phthalic group, thus decreasing the total free volume of the polymer. A further increase in the number of methyl or isopropyl substituent groups enlarges the interchain distance and the free volume greatly. This explanation is supported by density measurement experiments to characterize free volume (cf Table III).

Table III. Polymer

Density and Free Volume of PEK-C's

Ρ (g/cm ) V(cm /g) V (cm3/g)* V (cm3/ ) PEK-C 1.249 0.801 0.677 0.124 DMPEK-C 1.247 0.805 0.112 0.693 TMPEK-C 1.195 0.833 0.131 0.706 DIDMPEK-C 1.140 0.877 0.718 0.159 * V is calculated by the method of Sudgen(70). 3

3

0

F

g

CED(kJ/cm3)** 458.4 474.8 429.1 418.6

0

** CED is estimated by a group contribution method^ 1). In the case of TMPEK(S)-C, both permeability and permselectivity were increased simultaneously relative to PEK(S)-C. More detailed studies are being pursued to clarify the origin of this effect. PEK(S)-C Polymers with Side Carboxylic Group Cross-linking polymers by radiation, chemical or photochemical means can increase permselectivity by decreasing the permeability of larger gases more than that of smaller gases. The permselectivity can be increased as much as thirty times ( α H /N increased from 47 to 1400) by photochemical crosslinking of a polyether-imide made 2


2


273 from benzophenone dianhydride and diphenyletherdiamine(72). After crosslinking, polymers lose their solubility in solvents and cannot be processed anymore. On the other hand, polymers with carboxylic or other pendent groups, which are capable of forming hydrogen or ionic bonds between the polymer chains may be regarded as polymers with physical crosslinks. Such polymers are still soluble in solvents and hydrogen bonds formed at room temperature can usually be broken by increasing the temperature to processing temperature. The ability of hydrogen bonding in PEK(S)C to enhance permselectivity has already been shown for the PEK(S)-H family of polymers^. In this study, phenolphthalein and diisopropyldimethylphenolphthalein were reduced in alkaline solution by Zn dust with lactone ring opening to phenolphthalin (PPL) and diisopropyldimethylphenolphthalin (DIDMPPL) (7,8) with good yield. In the process of polycondensation, the pendent carboxylic groups were protected by formation of the Κ salt. It was shown that no pendent carboxylic group took part in the nucleophilic polycondensation with dinitrobenzophenone or dichlorodiphenylsulfone in DMSO to give the following polymers:

Polymer

Η

R Η CH Η

CH3

CH3

Rl Η CH3

PEK-L DIDMPEK-L PES-L DIDMPES-L

3

X

R Η

R3 Η

2

4

CH(CH )2 Η

CH(CH )2 Η

CH(CH )2

CH(CH )2

3

c=o c=o

3

3

S02 S02

3

Table IV. Gas permeation properties of polyetherketone(sulfone)s with side carboxylic group at 30°C Polymer PEK-C PES-C PEK-L PES-L DIDMPEK-L DIDMPES-L Ρ in barrers.

PH

2

11.7 12.1 7.26 7.22 49.7 49.6

α H /N 2

75.5 72.6 150 165 42.1 65.5

2

Po

2

0.95 0.95 0.49 0.44 7.20 4.53

α o /N 2

6.2 6.2 10.1 9.24 6.10 5.98

2

Pco

2

α CO /CH

2.73 5.74 1.81 2.25 22.8 25.1


2

33.2 40.1 43.6 57.0 16.9 22.3

4

274


The procedures for membrane casting and gas permeability measurement were the same as above. The permeability of water vapor was measured separately according to G B 1037-70 (China). The gas permeation properties of PEK(S)-L and DIDMPEK(S)-C are shown in Table IV. In comparison with the PEK(S)-C's, the PEK(S)-L's have much higher gas selectivity (as expected) at the expense of a slight decrease in permeability. The DIDM-substituted PEK(S)-L's, on the other hand, are 5-10 times more permeable than their unsubstituted analogs and exhibit permselectivity vallues similar to those of PEK(S)-L. These materials are promising candidates for the next generation of gas separation membrane materials. Ionomers from PEK(S)-L. When PEK(S)-L membranes were soaked in K O H or NaOH solution overnight and then washed with water and dried, ionomer type membranes were obtained. Analyses show complete salt formation (i.e. no free acid groups), and the monovalent alkali metal ion, K+ or N a , was coordinated with several carboxylic groups to form clusters. +

The gas permeation properties of these ionomer membranes are recorded in Table V . As shown in Table V , the ionomers achieve the highest permselectivity of all of the modifications of PEK(S)-C studied: around 300 for the hydrogen/nitrogen gas pair, >11 for oxygen/nitrogen and 276,000 for water vapor/nitrogen.

Table V . Gas permeation properties of Ionomers from PEK(S)-L at 30°C Polymer PH Po2 α o /N P H O α H 0 / N PN α H /N 2

PEK-L PEK-Na PEK-K DIDMPEK-L PES-L PES-Na PES-K DIDMPES-L Ρ in barrers.

2

7.26 4.67 3.95 49.7 7.22 5.05 4.89 49.6

0.049 0.023 0.013 1.18 0.044 0.026 0.018 0.76

2

150 202 302 42.1 165 242 269 65.5

2

2

0.49 0.24 0.155 7.20 0.404 0.281 0.208 4.53

10.0 10.4 11.8 6.10 9.24 10.7 11.4 5.98

2

2

2

1349 5860

27800 254000

2840 7260

65000 276000

5050

6670

2

The Po2 vs. α o /N and P H 2 vs. α H / N plot for the modified PEK(S)-C polymers together with common polymers are presented in Figures 1 and 2. As can be seen from the plot, most of the polymers synthesized in this work are located above the "upper bound line" (13). 2

2

2

2


275

\


10

r 3'·

r

\ ·

2

'

\

8

1

5

„ 7 3 6 ο ο ο 8\ 1 \ ο

\

• τ

0.1

8'·\ :—ι 3

1

1_ ,

4

5 α

Figure 1. Ρ

2

I

6 0 /Ν 2

7

é

4

2

vs. α / for modified PEK(S)-C polymers. 1: PES-C, 2: DMPES-C, 2 2 2 3: T M P E S - C , 4: DIDMPES-C, 5: P E K - C , 6: D M P E K - C , 7: T M P E K - C , 8: D I D M P E K - C , Γ : PMP, 2': PPO, 3': E C , 4': PSF, 5': PC, 6': PP, 7': Kapton, 8': Ube's PI. 0

0

Ν

10

30

50

70 Α

90 H /N 2

Figure 2. P

110 130 150

2

vs. a / for modified PEK(S)-C polymers. 1: PES-C, 2: DMPES-C, 2 2 2 3: T M P E S - C , 4: DIDMPES-C, 5: P E K - C , 6: D M P E K - C , 7: T M P E K - C , 8: DIDMPEK-C, Γ : PMP, 2': PPO, 3': C A , 4': PSF, 5': PC, 6': PP, 7': Kapton, 8': Ube's PI. H

H

N


276 Literature Cited


1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Liu, K.J.; Zhang, H.C.; Chen, T.L. Chin. Pat. C N 85,101,721 1987. Zhang, H.C.; Chen, T.L.; Yuan, Y.G. Chin. Pat. C N 85,108,751 1987. Chen, T.L.; Yuan, Y.G.; Xu, J.P. Chin. Pat. C N 88,102,291 1991. Chen, T.L.; Yuan, Y.G.; Xu, J.P. Preprints of ICOM'87, Tokyo, 1987, p.249. Liu, W.Y.; Wang, Z.G.; Chen, T.L.; Xu, J.P. Proceedings of ICOM'90, Chicago, 1990, p.836. Moe, M.B.; Koros, W.J.; Paul, D.R. J. Polym. Sci.: Polym. Phys. Ed. 1988, 26, 1931. Wang, Z.G. doctoral dissertation, CIAC CAS, Changchun, 1994. Wang, Z.G.; Chen, T.L.; Xu, J.P. J. Appl. Polym. Sci., 1997, 63, 1127. Wang, Z.G.; Chen, T.L.; Xu, J.P. J. Appl. Polym. Sci., 1997, 64, 1725. Sudgen, S. J. Chem. Soc, 1927, 1786. Jeans, J. An Introduction to the Kinetic Theory of Gases; Cambridge Univ. Press: London, 1982, p. 183. Liu, Y.; Ding, M . X . ; Xu, J.P. Procedings of IMSTEC '92, Sydney, Australia, Nov. 1992, p.240. (paper E2-7) Robeson, L . M . J. Membrane Sci., 1991, 62, 165.


Polymer Membranes for Gas and Vapor Separation - American

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