Effect of UV Crosslinking on Transport Properties of CO2 and N2 Through Poly(Imide-siloxane) Segmented Copolymer

Crosslinkable segmented random copolymers are made by synthesizing a polyimide in the presence of bisaminopropyl dimethylsiloxane (PDMS) oligomers. The polyimide segments of these materials are composed of two different dianhydrides, 2,2’-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), and 3,3’,4,4’- benzophenone tetracarboxylic dianhydride (BTDA) with the base diamine, 2,4,6-trimethyl-1,3-phenylenediamine (DAM). Upon irradiation with UV light, the ketone group in BTDA can form radicals that crosslink with adjacent benzylic methyl groups on DAM. Thermal analysis reveals that siloxane-containing polyimide copolymer films are phase segregated, composed of a polyimide-rich continuous phase and dispersed PDMS phase. CO2 and N2 gas permeabilities of uncrosslinked and crosslinked samples were measured to investigate the effect of UV crosslinking on permeability and permselectivity. Incorporation of PDMS did not significantly change the transport properties of the membranes. Densification occurred as a result of UV crosslinking, which enhanced the size-sieving capability of the poly(imide-siloxane) segmented copolymer membrane.