Functional Bisphenol-Based Additive for Controlled Gas Transport and Suppressed Plasticization of Polyimide Membranes

This paper describes a rationally designed, small-molecule additive that alters the physical properties of polyimide membranes. The additive molecule has a bisphenol-based core that can sufficiently interact with the polyimide backbone and a compatibilizer that ensures uniform distribution on a molecular level. Upon postcasting heat treatment, in situ morphing of the additive is caused to induce additional noncovalent interactions, reinforcing the matrices and affecting their gas transport properties. By incorporating 1 wt % small-molecule additives, the polymer chain packing structure of the polymer matrix was noticeably modified. This feature resulted in an improvement in gas selectivity for gas pairs with large kinetic size differences, such as CO2 or H2 discrimination from CH4 or N2. Moreover, the CO2 plasticization phenomenon was dramatically suppressed due to the formation of a noncovalent-induced rigid polymer chain arrangement. This design concept could be advanced by employing a variety of core and compatibilizer units or adapting it to other external stimuli, allowing stimuli-responsive additives for gas separation membranes.