Patent ID: 9718032
Date: 2017-08-01
CPC Classifications: B01D,C08G,C08L,Y02C,Y02P

Claim:
1. A method of making a membrane comprising an uncrosslinked high molecular weight, monoesterified polyimide, the method comprising: (a) preparing a polyimide comprising carboxylic acid functional groups from a reaction solution comprising monomers and at least one solvent, wherein the monomers comprise (i) a dianhydride monomer, (ii) a diamino monomer without carboxylic acid functional groups, (iii) a diamino monomer with carboxylic acid functional groups, and (iv) a bulky diamino compound different from the diamino monomers (ii) and (iii), wherein 2 to 10 mole % of the total diamino monomers comprise the bulky diamine compound; (b) treating the polyimide with a diol at esterification conditions in the presence of dehydrating conditions to form an uncrosslinked monoesterified polyimide, wherein the dehydrating conditions at least partially remove water produced during step (b); and (c) obtaining a membrane comprising the uncrosslinked monoesterified polyimide polymer comprising less than 30% by weight ester crosslinks.