Triptycene-based copolyimides with tailored backbone rigidity for enhanced gas transport

A series of triptycene-based copolyimides with varying backbone rigidity was synthesized and evaluated for chain packing behavior and gas transport properties. These copolymers were composed of a rigid element with the triptycene skeleton directly linked to imide rings and a relatively flexible element containing ether linkage and CF3 substituent groups. The ratio of the two components was systematically varied to investigate the effect of increasing triptycene density and steric hindrance while decreasing CF3 and ether linkage density. Generally, increasing the percentage of the directly-linked triptycene component increased chain rigidity, interchain spacing, and fractional free volume due to more highly disrupted chain packing. Therefore, copolymers with a high fraction of the directly-linked component showed increased gas permeabilities compared to the relatively flexible homopolymer counterpart. Additionally, the increase in triptycene density introduced more ultra-fine microcavities to facilitate in sieving, allowing for a concurrent maintenance or increase in selectivity. (C) 2017 Elsevier Ltd. All rights reserved.