6FDA‐TAPOB hyperbranched polyimide‐silica hybrids for gas separation membranes

Physical and gas transport properties of hyperbranched polyimide‐silica hybrid membranes were investigated. Hyperbranched polyamic acid as a precursor was prepared by polycondensation of a triamine, 1,3,5‐tris(4‐aminophenoxy) benzene (TAPOB), and a dianhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and subsequently modified a part of end groups by 3‐aminopropyltrimethoxysilane (APTrMOS). The hyperbranched polyimide‐silica hybrid membranes were prepared by sol–gel reaction using the polyamic acid, water, and alkoxysilanes. 5% weight‐loss temperature of the hybrid membranes increased with increasing silica content, indicating effective crosslinking at polymer‐silica interface mediated by APTrMOS moiety. On the other hand, glass transition temperature of the hybrid membranes prepared with methyltrimethoxysilane (MTMS) showed a minimum value at low silica content region, suggesting insufficient formation of three‐dimensional SiOSi network compared to the hybrid membranes prepared with tetramethoxysilane (TMOS). CO2, O2, N2, and CH4 permeability coefficients of the hybrid membranes increased with increasing silica content. Especially for TMOS/MTMS combined system, the hybrid membranes showed simultaneous enhancements of gas permeability and CO2/CH4 separation ability. It was concluded that the 6FDA‐TAPOB hyperbranched polyimide‐silica hybrid membranes have high thermal stability and excellent CO2/CH4 selectivity and are expected to apply to high‐performance gas separation membranes.