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A composition of and a method of making high performance hollow fiber membranes is described. The membranes have a high resistance to plasticization by use of a predetermined amount of crosslinking. The preferred polymer material for the membrane is a polyimide polymer comprising covalently bonded e

A composition of and a method of making high performance hollow fiber membranes is described. The membranes have a high resistance to plasticization by use of a predetermined amount of crosslinking. The preferred polymer material for the membrane is a polyimide polymer comprising covalently bonded ester crosslinks. The resultant hollow fiber membrane exhibits a high permeability of CO2 in combination with a high CO2/CH4 selectivity. Another embodiment provides a method of making the hollow fiber membrane from a monesterified polymer followed by final crosslinking after hollow fiber formation.

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1. A hollow fiber polymer membrane, comprising:a crosslinked polyimide polymer having covalent ester crosslinks; and having a CO2 permeance of at least 20 GPU and a CO2/CH4 selectivity of greater than 20, at 35 degrees C. and a pressure of 100 psia. 2. The hollow fiber polymer membrane of claim 1 wh

1. A hollow fiber polymer membrane, comprising:a crosslinked polyimide polymer having covalent ester crosslinks; and having a CO2 permeance of at least 20 GPU and a CO2/CH4 selectivity of greater than 20, at 35 degrees C. and a pressure of 100 psia. 2. The hollow fiber polymer membrane of claim 1 wherein the polyimide is 6FDA.3. The hollow fiber polymer membrane of claim 1 wherein the covalent ester crosslinks are formed by the monoesterification of an uncrosslinked polyimide polymer having carboxylic acid sites incorporated therein, with a diol, followed by transesterification, to form a crosslinked polyimide polymer.4. The hollow fiber polymer membrane of claim 3 wherein the diol is selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, benzenedimethanol, and 1,3 butanediol.5. A hollow fiber polymer membrane, comprising:a crosslinked polyimide polymer having at least some covalent ester crosslinks and having a ratio of crosslinkable sites to imide groups of between 3:8 and 1:16. 6. A hollow fiber polymer membrane, comprising:a polyimide polymer made from the monomers A+B+C; where A is a dianhydride of the formula; where X1 and X2 are the same or different halogenated alkyl group, phenyl or halogen; where R1, R2, R3, R4, R5, and R6 are H, alkyl, or halogen; where B is a diamino cyclic compound without a carboxylic acid functionality; where C is a diamino cyclic compound with a carboxylic acid functionality; and wherein the ratio of B to C is between 1:4 and 8:1, and wherein said hollow fiber polymer membrane further comprises at least some covalent ester crosslinks. 7. The hollow fiber polymer membrane of claim 6 where X1 and X2 are CF3.8. The hollow fiber polymer membrane of claim 6 where R1, R2, R3, R4, R5, and R6 are H.9. The hollow fiber polymer membrane of claim 6 wherein the dianhydride is 6FDA.10. The hollow fiber polymer membrane of claim 6 wherein C is DABA.11. The hollow fiber polymer membrane of claim 6 wherein B is a diamino aromatic compound.12. The hollow fiber polymer membrane of claim 6 wherein B is a methyl substituted diamino benzene.13. The hollow fiber polymer membrane of claim 6 wherein the ratio of B to C is between 17:3 and 3:2.14. The hollow fiber polymer membrane of claim 6 wherein the ratio of B to C is between 17:3 and 3:1.15. The hollow fiber polymer membrane of claim 6 wherein said ester crosslinks are made using a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, benzenedimethanol, and 1,3 butanediol.16. The hollow fiber polymer membrane material of claim 15 wherein the ester crosslinks are made by formation of a monoester, at monoesterification conditions, followed by formation of the ester crosslinks by transesterification of the monoester, at transesterification conditions to from a crosslinked hollow fiber polymer membrane.17. The hollow fiber polymer membrane material of claim 6 wherein the ratio of B to C is between 4:1 and 3:2.18. The hollow fiber polymer membrane of claim 6 wherein the polyimide polymer has an average molecular weight of between 20,000 and 200,000.19. The hollow fiber polymer membrane material of claim 6 wherein the membrane material has an average molecular weight greater than the entanglement MW of the polymer.20. The hollow fiber polymer membrane material of claim 6 wherein the membrane material has an average molecular weight of between 40,000 and 140,000.21. A method of making a crosslinked hollow fiber membrane, comprising:preparing a polyimide polymer comprising a predetermined quantity of crosslinkable sites; treating the polyimide polymer with a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, and 1,3 butanediol, at esterification conditions, to form a monoesterified polymer; forming a monoesterified hollow fiber from the monoesterified polymer; and subjecting the monoesterified hollow fiber to transesterification conditions to form a covalently crosslinked hollow fiber membrane. 22. The method of making a crosslinked hollow fiber membrane of claim 21 wherein the polyimide polymer is treated with a diol in the presence of an esterification catalyst.23. A method of making a crosslinked hollow fiber membrane, comprising:preparing a polyimide polymer comprising a predetermined quantity of crosslinkable sites; forming a hollow fiber from said polyimide polymer; treating the hollow fiber with a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, and 1,3 butanediol, at esterification conditions, to form a monoesterified hollow fiber; and subjecting the monoesterified hollow fiber to transesterification conditions to form a crosslinked hollow fiber membrane.