Highly Selective Soluble Polyimides Simultaneously Containing Benzimidazole and Hydroxyl Groups for Membrane-Based Gas Separation
Haoqi Sang, Jun Zhou, Fan Hu, Kai Geng, Shichao Feng, Hanli Wang, Yongbing Zhuang
Abstract
A diamine monomer 5-amino-2-(4-hydroxy-3-aminobenzene)-benzimidazole (OH-BIA) containing both benzimidazole and hydroxyl groups was synthesized through a facile two-step reaction and polymerized with four commercially available dianhydrides to yield four polyimides. The solubility, chain packing, mechanical performance, thermal stability, and gas transport properties of the synthesized polyimides were investigated in detail. The synthesized polyimides exhibited good solubility, excellent mechanical properties (tensile strengths ≥103.3 MPa), high thermal stability and glass-transition temperatures (≥396 °C), and high gas selectivity due to the simultaneous introduction of benzimidazole and hydroxyl groups. In particular, because of their enhanced size-sieving ability, these polyimide membranes exhibited higher ideal selectivity for some gas pairs such as CO 2 /CH 4 (up to 116) compared to commercial Matrimid 5218 (selectivity for CO 2 /CH 4 is 36) and other reported polyimide dense membranes (selectivity for CO 2 /CH 4 is up to 63). This work provides useful insights into the design of highly selective polyimides for membrane-based gas separation.