# US 8,772,417 B2 · Polyimide membranes and their preparation

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- Number: US 8,772,417 B2
- Document ID: US8772417B2
- Status: Granted
- Kind: B2
- Application number: 13/640,439
- Filed: 2011-04-12
- Published: 2013-02-21
- Granted: 2014-07-08
- Earliest claimed: 2010-04-12
- Assignees: National University of Singapore
- Applicants: Youchang Xiao; Tai-Shung Chung; Mei Ling Chua; Mohammad Askari; Rui Chin Ong
- Inventors: Youchang Xiao; Tai-Shung Chung; Mei Ling Chua; Mohammad Askari; Rui Chin Ong
- Web page: https://patentgrep.com/patent/US8772417B2

## CPC

- C08G 73/101: {containing chain terminating or branching agents}
- C08J 5/2256: {based on macromolecular compounds obtained by reactions other than those involving carbon-to-carbon bonds, e.g. obtained by polycondensation}
- C08L 79/08: Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
- C08J 2379/08: Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)

## Abstract

Disclosed are (1) a method of preparing a polyimide membrane, including cross-linking polyimides via thermal labile side chains and decomposition of the thermal labile side chains; and (2) polyimide membranes thus prepared.

## Claims

### Claim 1

A method for preparing a polyimide membrane comprising:
providing a solution containing a solvent and grafted polyimides, the grafted polyimides having molecular weights of 10,000-300,000 and containing monomers A and, optionally, also containing monomers B;
each of the monomers A, which are the same or different, having the following formula:
and each of the monomers B, which are the same or different, having the following formula:
in which
each of the Ar1 moieties, independently, is
each of the Z moieties, independently, being C(CF3)2, C(═O), O, S, S(O2), C(CH3)2, CH2, or O(-Ph-)O;
each of the Ar2 moieties, independently, is
each of the X, X1, X2, and X3, independently, being H, C1-C5 alkyl, C1-05 alkoxyl, phenyl, and phenyoxyl; and each of the Y moieties, independently, being C(CF3)2, C(═O), O, S, S(O2), C(CH3)2, CH2, or O(-Ph-)O;
each of the Ar3 moieties, independently, is
each of the R moieties, independently, being C(CF3)2, C(═O), O, S, S(O2), C(CH3)2, CH2, or O(-Ph-)O; each of the R1 moieties, independently, being H, C1-C5 alkyl, C1-C5 alkoxyl, phenyl, and phenyoxyl; each of the n values, independently, being 0, 1, 2, or 3; and
each of the T moieties, independently, is a thermal labile side chain containing a —O— group linked to the carbonyl group in the Ar3 moiety in a monomer A, and also containing at least one hydroxyl group;
evaporating the solvent to form a membrane;
cross-linking Ar3 moieties via T moieties by covalent bonding therebetween to form a cross-linked membrane, the covalent bonding resulting from reaction between the hydroxyl group in a T moiety and the carbonyl group in an Ar3 moiety; and
heating the cross-linked membrane so as to both decompose the T moieties and form covalent bonds between aryl rings in the Ar1, Ar2, and Ar3 moieties,
wherein, if the grafted polyimides also contain the monomers B, the molar ratio of the monomers B to the monomers A is 0.11 to 99, and a monomer A and a monomer B are linked as follows:

### Claim 2 (depends on 1)

The method of claim 1, wherein the solution further includes ungrafted polyimides, having molecular weights of 10,000-300,000 and containing monomers A′ and, optionally, also containing monomers B as defined in claim 1 above;
each of the monomers A′, which are the same or different, having the following formula:
in which
each of the Ar1 moieties and each of the Ar3 moieties are defined in claim 1; and
T′ is a —OH group, linked to the carbonyl group in the Ar3 moiety in a monomer A′, wherein, if the ungrafted polyimides also contain the monomers B, the molar ratio of the monomers B to the monomers A′ is 0.11 to 99, and
a monomer A′ and a monomer B are linked as follows:

### Claim 3 (depends on 2)

The method of claim 2, wherein the grafted polyimides have molecular weights of 30,000-70,000, the ungrafted polyimides have molecular weights of 30,000-70,000, the molar ratio of the monomers B to the monomers A is 0.33 to 19, and the molar ratio of the monomers B to the monomers A′ is 0.33 to 19.

### Claim 4 (depends on 2)

The method of claim 2, wherein each of the T moieties, independently, is R2—CH2—O—, R2 being CnH2n+2−x(OH)x, in which x is 2-30 and n is 2-30.

### Claim 5 (depends on 2)

The method of claim 2, wherein each of the T moieties, independently, is
glucose or
in which p is 1-9; and each of the X4 moieties, independently, is H, C1-C5 alkyl, C1-C5 alkoxyl, phenyl, or phenyoxyl.

### Claim 6 (depends on 5)

The method of claim 5, wherein p is 6 and X4 is H.

### Claim 7 (depends on 6)

The method of claim 6, wherein Ar1 is
Z being C(CF3)2; Ar2 is
each of X, X1, X2, and X3, being CH3; Ar3 is
the molar ratio of the monomers B to the monomers A is 9; and the molar ratio of the monomers B to the monomers A′ is 9.

### Claim 8 (depends on 5)

The method of claim 5, wherein p is 0.

### Claim 9 (depends on 8)

The method of claim 8, wherein Ar1 is
Z being C(CF3)2; Ar2 is
X, X1, X2, and X3, being CH3; Ar3 is
the molar ratio of the monomers B to monomers A is 1, and the molar ratio of the monomers B to the monomers A′ is 1.

### Claim 10 (depends on 2)

The method of claim 2, wherein the cross-linking step is induced thermally.

### Claim 11 (depends on 2)

The method of claim 2, wherein the heating step is performed at 350-450° C.

### Claim 12 (depends on 1)

The method of claim 1, wherein the grafted polyimides have molecular weights of 30,000-70,000 and the molar ratio of the monomers B to the monomers A is 0.33 to 19.

### Claim 13 (depends on 1)

The method of claim 1, wherein each of the T moieties, independently, is R2—CH2—O —, R2 being CnH2n+2−x(OH)x, in which x is 2-30 and n is 2-30.

### Claim 14 (depends on 1)

The method of claim 1, wherein each of the T moieties, independently, is
glucose or
in which p is 1-9; and each of the X4 moieties, independently, is H, C1-C5 alkyl, C1-C5 alkoxyl, phenyl, or phenyoxyl.

### Claim 15 (depends on 14)

The method of claim 14, wherein p is 6 and X4 is H.

### Claim 16 (depends on 15)

The method of claim 15, wherein Ar1 is
Z being C(CF3)2; Ar2 is
each of X, X1, X2, and X3, being CH3; Ar3 is
the molar ratio of the monomers B to the monomers A is 9, and the molar ratio of the monomers B to the monomers A′ is 9.

### Claim 17 (depends on 14)

The method of claim 14, wherein p is 0.

### Claim 18 (depends on 17)

The method of claim 17, wherein Ar1 is
Z being C(CF3)2; Ar2 is
X, X1, X2, and X3, being CH3; Ar3 is
the molar ratio of the monomers B to monomers A is 1, and the molar ratio of the monomers B to the monomers A′ is 1.

### Claim 19 (depends on 1)

The method of claim 1, wherein the cross-linking step is induced thermally.

### Claim 20 (depends on 1)

The method of claim 1, wherein the heating step is performed at 350-450° C.

### Claim 21 (depends on 1)

A polyimide membrane prepared by the method of claim 1.

### Claim 22 (depends on 2)

A polyimide membrane prepared by the method of claim 2.