A top-down and bottom-up strategy to generate free volume for membrane-based gas separations*

Polymers of intrinsic microporosity (PIMs) have outstanding gas permeabilities and adequate selectivities. These properties result from the rigid and contorted backbone structure of PIMs, which produce significant non-equilibrium free volume as these polymers vitrify during solvent casting. Unfortunately, it is difficult to manipulate and predict the nascent free volume architecture of these polymers. This presentation will describe two alternative strategies to generate high free volume polymers. The first strategy is to construct bottlebrush polymers with pre-designed side chains that can generate free volume. In this bottom-up approach, rigid side chains are tethered to flexible backbones to generate a new class of PIM materials. The second strategy is a top-down approach, where a polymer is pre-functionalized with a labile protecting group. After casting, in situ solid-state deprotection and crosslinking significantly increases free volume and tightens free volume distribution, resulting in enhanced permeability and selectivity for various gas pairs.