(705d) Facile Approach to Simultaneously Reducing Physical Aging and Swelling While Enhancing Permeability in Microporous Polymer Membranes

Although exhibiting superb performance in the short time operation, microporous and ultra-microporous glassy polymers suffer from physical aging and swelling, which hampers their scale up to the industrial level in gas, vapor as well as organic solvent separations. In this study, we propose a facile approach to manipulate free volume morphology and distribution, as well as polymer chain dynamics, to reduce physical aging and swelling in microporous glassy polymers, while enhancing gas permeability. A model microporous high free volume glassy polymer, PTMSP, was blended with 5wt.% hyper cross-linked triptycene-isatin porous polymer network exhibiting configurational free volume. As a result, gas permeability increased by a factor of three compared to neat PTMSP, with a minor loss in ideal selectivity. Simultaneously, polymer swelling in the presence of high pressure CO₂ and physical aging rate were substantially reduced. The combination of PALS analysis, density measurements and free volume calculations indicate that blending with PPN provides a unique opportunity to exquisitely tune the size and architecture of free volume elements, leading to the above mentioned enhancement of permeability, physical aging and swelling resistance. The molecular mechanism by which these effects take place was elucidated in detail, and possible strategies to enhance selectivity other than permeability and long-term stability were devised.

Remarkably, although the incorporation of PAFs (Porous Aromatic Frameworks) in high free volume glassy polymers can successfully slow down the aging rate while enhancing gas permeability and retaining selectivity,their cost is very high and their synthesis pathway complicate, which hampers their industrial scale-up. In sharp contrast, the PPNs synthesis pathway is easy and one order of magnitude cheaper, which makes our approach highly scalable.