Gas transport properties of truxene-based network polyimide membrane with flexible hexyl side chains

Abstract

Crosslinking is a viable way to construct the network polymers which possesses the merits of high rigidity, excellent plasticization resistances, and good thermal stability using in the area of gas separation. However, dependence on crosslinking method often leads to contracted pores among polymer chains and in turn, sacrifices gas permeability seriously. In this work, a novel truxene triamine monomer with flexible hexyl side chains (termed as HTUTA) was designed, synthesized, and subsequently reacted with three different dianhydrides ODPA, BTDA, and 6FDA though polycondensation to obtain a series of network polyimides (PIs) membranes. Among these three designed truxene-based network PIs, HTUTA-6FDA had the best overall gas separation performance rooting from its bulky –C(CF3)2- moieties within the polymer framework. Compared with our previous reported TAPA-6FDA and TAPB-6FDA, the overall gas transport properties of the newly designed truxene-based network PIs are enhanced obviously because of incorporating the bulky and flexible side chains as well as enhancing the polymer backbone rigidity via using the truxene structure as the building block. For instance, the gas permeability of designed HTUTA-6FDA for CO2 and O2 were, respectively, enhanced 261% and 253% in comparison with these of TAPB-6FDA. In addition, benefiting from the flexible hexyl side chains, the partial chain segment motion was increased and accordingly the inter- and intra-chain interactions were minimized. Thus, a broad operating flexibility without the risk of gelation could be achieved during the tridimensional polycondensation process, which is extremely significant to their practical production. We hope this study can open a new insight into the rational design of the network PI membranes with enhanced gas permeability as well as no risk of gelation trend before film-forming.