Alicyclic segments upgrade hydrogen separation performance of intrinsically microporous polyimide membranes

Even with high permeability, insufficient selectivity of intrinsically microporous polyimides is a major obstacle for large-scale membrane-based separation applications. The present work proposes to increase hydrogen separation performance by incorporating deliberately chosen alicyclic segments into Troger's Base (TB)-based polyimide backbones via copolymerization. The resulting TB-based copolyimides showed the best hydrogen separation performance (e.g., H-2/CH4, H-2/N-2 and H-2/CO2) among all state-of-the-art TB-based polyimide materials reported to date. An important contribution of enhancement in solubility selectivity to increase hydrogen separation performance was investigated for the first time in this study. The introduction of alicyclic segments significantly promoted the Langmuir affinity parameters of H-2, thereby improving H-2 solubility over other gas solubilities (CH4, N-2 and CO2). Herein, the unique backbone architecture highlights the possibility of accessing membranes characterized by favorable hydrogen separation performance in adverse/harsh environments, as well as by solution processability, desirable physical properties for large-scale separation applications.