Structure–property relationships of hyperbranched polyimide–silica hybrid membranes with different degrees of modification

Abstract

AbstractThe physical and gas transport properties of hyperbranched polyimide (HBPI)–silica hybrid membranes with different degrees of modification prepared with a dianhydride, 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride, a triamine, 1,3,5‐tris(4‐aminophenoxy) benzene, and a coupling agent, 3‐aminopropyltrimethoxysilane, were investigated. With increasing degree of modification, the inherent viscosity of the hyperbranched poly(amic acid) increased, and the density of the HBPI decreased; this suggested the formation of crosslinking through the coupling agent. Dynamic mechanical analysis and thermomechanical analysis measurements indicated that the mobility of the HBPI molecular chains decreased in the rubbery region and that the free‐volume holes of the HBPI increased in the glassy region because of the increased degree of crosslinking through the coupling agent. The CO2 permeability and CO2/CH4 permselectivity of the HBPI–silica hybrid membranes increased with increasing silica content, with the latter increase being remarkable for the HBPI–silica hybrid membranes with a higher degree of modification. This suggested that the pronounced improvement in the CO2/CH4 permselectivity of the highly modified HBPI–silica hybrid membranes was likely caused by the contributions of both the intrinsic high‐fractional free volume attributed to crosslinking through the coupling agent and the characteristic distribution and interconnectivity of free‐volume holes created by hybridization with silica. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013