Asymmetric modified carbon molecular sieve hollow fiber membranes having improved permeance

A process for preparing a thermally rearranged polymer material having improved gas separation performance properties comprising:

• a. providing a polymer precursor material comprising a polyimide with an ortho-positioned functional group,
• b. contacting the polymer precursor material with a solution comprising a modifying agent and a non-aqueous solvent, wherein the modifying agent is
• a compound having the general formula R1R2R3R4Si, where each of R1, R2, R3, and R4 are independently C1-C6 alkyl or alkenyl, alkoxy, or halogen;
• with the proviso that the compound contains at least one C1-C6 alkyl or alkenyl substituent and at least one alkoxy or halogen substituent, or
• a compound having the general formula R1R2R3R4M, where M is a metal and where each of R1, R2, R3, and R4 are independently C1-C6 alkyl or alkenyl, alkoxy, or halogen, with the proviso that the compound contains at least one C1-C6 alkyl or alkenyl substituent and at least one alkoxy or halogen substituent,
• c. contacting the polymer precursor material of step b. with a moisture-containing atmosphere to form a treated polymer precursor material, and
• d. heating the treated polymer precursor material to form a thermally rearranged polymer.