Gas separation membranes obtained by partial pyrolysis of polyimides exhibiting polyethylene oxide moieties

Aromatic copolyimides (PIx) and aromatic-aliphatic copolyimides (PIxEOy) were synthesized by reacting 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) with mixtures obtained from 2,2'-bis(4-aminophenyl) hexafluoropropane (6FpDA), 5-diaminobenzoic acid (DABA) and Jeffamine ED-2003 (PEO). The selective thermal removal of PEO from PIxEOy yielded membranes with high thermal stability and good mechanical properties. The presence of carboxylic groups minimized the shrinkage during the cross-linking process. The membranes containing 10 mol% DABA exhibited good O-2/N-2 and CO2/CH4 separation perfor-mance, and resistance to CO2 plasticization. PIx/PIxEOy blends containing less than 10 wt% PEO were prepared. The CO2/CH4 selectivity/permeability balance of cross-linked membranes largely exceeded that of PIx. The results highlight a possible strategy for using analogous cross-linkable polymers exhibiting ethylene oxide moieties as mere additive to prepare high free volume polyimide's membranes, exhibiting enhanced separation properties and high resistance to plasticization.