Polymer Morphological Effect on Gas Transport within Triptycene-Based Polysulfones

In this study, the effect of polymer morphology on chain packing and physical and gas transport properties was explored via the creation and study of three polysulfone copolymer membranes-a random copolymer, 15k-15k (g/mol) multiblock copolymer, and polymer physical blend-each containing a 50:50 mol equiv of triptycene and phenolphthalein bridging units. These polysulfones with varied morphologies were directly compared to each other, as well as to their relevant triptycene- and phenolphthalein-based polysulfone homopolymer counterparts. Each polysulfone containing equivalent amounts of triptycene and phenolphthalein exhibited similar physical properties, densities, and fractional free volume results regardless of combination method. Similarly, gas permeation data followed an expected trend of performance between that of the two homopolymers for H-2/CH4 and O-2/N-2 separations. Uniquely, the random copolymer exhibited unexpected suppression of methane permeability and, to a lesser extent, nitrogen permeability, leading to the highest selectivities for CO2/CH4 and CO2/N-2 among the series. This can likely be attributed to the greater abundance of triptycene and phenolphthalein units in close proximity along the polymer backbone in the random copolymer, leading to synergistic performance effects from different inter- and intrachain interactions unattainable in the multiblock, physical blend, and homopolymers.