The effect of rigid side-chain functionality on free volume and gas transport properties of a methoxy functionalized polymer generated via ring-opening metathesis polymerization (OMe-ROMP) was recently reported. In this study, we elaborate on the role of side-chain length with respect to fractional free volume (FFV), BET surface areas, and pure-gas diffusivities and permeabilities. Additionally, direct sorption analysis of the OMe-ROMP polymer was investigated, revealing an unambiguous correlation between sorption capacity and free volume. As side chain length increased, sorption capacity and diffusivity of small molecules also increased, resulting in significant improvements in permeability with minimal changes in selectivity. For example, by increasing the sidechain length from n = 2 units to n = 5 units, we observed a 20-fold increase in CO2 permeability, but at the same time, CO2/CH4 selectivity decreased by only ~33%. Moreover, the plasticization resistance of OMe-ROMP with varying side-chain length was studied using high-pressure mixed-gas CO2/CH4 permeation experiments, demonstrating that longer side-chain units can be used to mitigate polymer plasticization under relevant conditions. From this study, we show that designing and controlling pore-generating side-chains on polymers provide a useful tool to manipulate free volume, polymer packing structure, and plasticization resistance for ROMP polymers for gas separations.

Systematic studies on side-chain length of pore-generating bottlebrush polymers for membrane-based separations

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.