Physical and gas transport properties of hyperbranched polyimide (HBPI)silica hybrid membranes prepared with a dianhydride monomer, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and triamine monomers, 1,3,5-tris(4-aminophenoxy)triazine (TAPOTZ), and 1,3,5-tris(4-aminophenyl)benzene (TAPB), were investigated and compared with those of 6FDA-TAPOB HBPI system synthesized from 6FDA and 1,3,5-tris(4-aminophenoxy)benzene (TAPOB). Glass transition and 5% weight-loss temperatures of the 6FDA-based HBPIsilica hybrid membranes were increased with increasing silica content. 6FDA-TAPOTZ HBPI system, however, showed relatively low 5% weight-loss temperatures, suggesting thermal instability of triazine-ring in the TAPOTZ moiety. CO2/CH4 permselectivity of the HBPIsilica hybrid membranes were increased with increasing silica content, tending to exceed the upper bound for CO2/CH4 separation. This result indicated that free volume elements effective for CO2/CH4 separation were created by the incorporation of silica for the HBPIsilica hybrid systems. Especially, 6FDA-TAPB HBPI system had high gas permeabilities and CO2/CH4 separation ability, arising from high fractional free volume and characteristic size and distribution of free volume elements. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012