Highly Carboxylate-Functionalized Polymers of Intrinsic Microporosity for CO₂-Selective Polymer Membranes

Abstract

Carboxylate-functionalized polymers of intrinsic microporosity (PIMs) are promising materials for gas separation application. However, highly carboxylate-functionalized PIMs (HCPIMs) have not been reported owing to overlooked intermediate products. Herein, we successfully prepared HCPIMs (∼92 mol % of carboxylic acid group) through a prolonged alkaline hydrolysis process (360 h). HCPIMs were found to be soluble in various organic solvents, such as tetrahydrofuran and dimethyl sulfoxide, and then free-standing HCPIM membranes could be prepared by the common solution casting method. The HCPIM membranes were found to have smaller interchain distances and higher CO2 affinity than original PIM-1 films. For example, small gas molecules, such as carbon dioxide, were effectively separated due to the enhanced diffusivity selectivity combined with the smaller cavity size. Further, strong interactions between carbon dioxide and the carboxylic acid groups increased solubility selectivity. These synergetic effects endowed the HCPIM membrane with a selectivity of 53.6 for CO2/N2 separation, the highest among reported chemically modified PIMs.