Superacid-catalyzed polymerization of Diimide-PMDA and BTFMA for gas separating membranes

Abstract

In this study, novel polymers with high imide characteristics were synthesized by superacid-catalyzed step-growth polymerization of Diimide-PMDA and BTFMA monomers, using trifluoromethanesulfonic superacid (TFSA) as catalyst. This one-step, room-temperature reaction is eco-friendly and enables rapid chain growth without high temperature conditions. The successful synthesis and incorporation of both monomers into the polymer backbone was confirmed by structural analysis. However, the newly formed BTFMA–PMDA polymer was completely insoluble in most organic solvents due to the dense imide core and its strong intermolecular interactions, preventing membrane processing and formation, which was the main aim of this study. To overcome insolubility, diphenyl ether (DPE) was introduced as a co-monomer, providing flexible linkages that disrupted rigid chain packing, resulting in two co-polymers with enhanced solubility but reduced PMDA content compared to the original polymer. The 20% PMDA sample was soluble in NMP, DMSO, and THF, while the 30% PMDA sample remained soluble only in NMP. The findings of this study demonstrate the potential of using superacid-catalyzed polymerization to produce soluble and selective imide-containing polymers by strategically engineering co-monomers to balance solubility and structural rigidity in the next-generation of gas separation membranes.