Fine-tuning the molecular structure of binaphthalene polyimides for gas separations

Abstract A set of new stiff and contorted polyimides were prepared to systematically link polymer structure with gas separation properties. Seven novel bridged binaphthalene polyimides were synthesized for this purpose using commercial dianhydrides pyromellitic dianhydride (PMDA), biphenyl-tetracarboxylic acid dianhydride (BPDA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). From these polyimides, freestanding membranes were prepared and tested on mixed gas CO 2 /CH 4 and CO 2 /N 2 separation performance. They were further characterized using WAXS and PALS and through the simulation of their free volume elements (FVEs) and gas separation properties. The binaphthalene polyimides had CO 2 /CH 4 and CO 2 /N 2 mixed gas selectivities of respectively 40 and 29 and mixed gas permeabilities of about 20 barrer for both gas mixtures.