Polymer Molecular Weight Effects on Gas Sorption in Carbon Molecular Sieve Materials Derived from 6FDA-DAM

Carbon molecular sieve (CMS) materials, formed through pyrolysis of polymeric precursors, can effectively distinguish between different gas molecules, making them attractive next-generation separation materials. Altering the repeat unit structures of polymeric precursors is a frequently pursued approach to fine-tune the properties of CMS membranes and sorbents. Precursor molecular weight, the effects of which are studied here, is a more subtle variable with minimal study dedicated to its effect on CMS structure and properties. Using high and low molecular weight batches of the fluorinated polyimide 6FDA-DAM as a precursor, we show that gas sorption in CMS has significant dependence on polymer molecular weight. These effects, observable as elevated sorption capacities for high molecular weight derived CMS, are most pronounced at low and moderate pyrolysis temperatures. We expect that additional free volume elements in the more-entangled, high molecular weight precursor play a significant role in micropore formation.