Characterization and gas transport properties of UV-irradiated polydimethylsiloxane (PDMS)-containing polyimide copolymer membranes

Abstract

The influence of UV irradiation on gas permeation properties of random segmented poly (imide-siloxane) (PIS) copolymer films was investigated. Random segmented copolymers were synthesized via ester-acid imidization from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) in a 7:3 M ratio with 2,4-diamino mesitylene (DAM) and varying amounts of a diamine terminated polydimethylsiloxane (PDMS) oligomer (Mn = 3000 g/mol). Solvent cast films of these copolymers were UV-irradiated on both sides in air at 365 nm, which induced crosslinking and photooxidation. Pure-gas permeabilities of H2, O2, N2, CH4, and CO2 were measured with upstream pressures ranging from 2 to 18 atm at 35 °C. Gas permeability coefficients of a series of PIS copolymers decreased, and selectivity of all gas pairs increased after UV irradiation due to a decrease in free volume by UV crosslinking and photooxidation.