Plasticization Suppression in Grafted Polyimide−Epoxy Network Membranes

Abstract

This paper considers the blending of epoxide and diamine components into a glassy polyimide structure (2,2‘-bis(3,4‘-dicarboxyphenyl) hexafluoropropane dianhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TMPDA) intended for use as a gas separation membrane. It is shown that the diamine component can react both with the epoxide component to form an epoxy network and with the polyimide backbone itself, leading to a complex grafted structure. Bulk density and X-ray diffraction results show that this leads to a denser, more amorphous membrane structure. This effect appears to be independent of the diamine structure. Gas permeability is reduced and selectivity increases, consistent with established free volume theory. Importantly, however, plasticization resistance also increases. This implies that membrane performance will be more robust when exposed to condensable gases such as carbon dioxide. In this particular case, the increase in plasticization resistance is possibly insufficient to warrant the lo...