Effect of thermal treatment on gas transport properties of hyperbranched polyimide–silica hybrid membranes

Physical and gas transport properties of thermotreated hyperbranched polyimide and its silica hybrid membranes were investigated. Thermal treatment at 450 °C resulted in partial degradation and rearrangement of molecular chains. Gas permeabilities of the hyperbranched polyimide membrane were remarkably enhanced by thermal treatment at 450 °C, compared to those of linear-type polyimide membrane with a similar chemical structure. The enhanced gas permeabilities were considered to be due to local deformation of molecular packing caused by thermal degradation and rearrangement of molecular chains, which provided an increase in free volume elements. In addition, for the hyperbranched polyimide–silica hybrid membrane treated at 450 °C, hybridization with silica brought about increases in gas permeabilities and improvement of CO2/CH4 separation ability. The prominent CO2/CH4 separation ability was attributed to the enhanced free volume elements induced by facilitated thermal degradation and rearrangement of molecular chains, as well as created around interfacial region between polymer and well-dispersed silica domains with a large surface area.