Katherine Mizrahi Rodriguez
Today, industrial gas separations such as CO2 removal from natural gas rely primarily on energy-intensive or environmentally unfriendly processes. Polymer membranes are a candidate for gas separations due to their low energy costs and mechanical stability, yet polymer performance is constrained by a trade-off between permeability and selectivity (separation efficiency). One path towards improving separation performance and tackling transport limitations is the development of diffusion-selective polymers like polymers of intrinsic microporosity (PIMs). PIMs’ rigidity and inefficient packing yields an interconnected structure with <2nm micropores, high surface areas, and, as a result, high permeability values. In this study, a leading microporous polymer, PIM-1, is used as a platform to study the effect of functionality and packing structure on gas transport performance. After incorporating carboxylic acid (–COOH), amine (–NH2), and tertbutoxyl (tBOC) chemical groups into PIM-1, pure gas transport measurements for industrially relevant gas pairs such as CH4/CO2 are carried out. The direct effects of side-group chemistry on performance and packing are compared for two hydrogen bonding and CO2 sorbing moieties (–COOH and –NH2); while pore blockage is studied using the tBOC protecting group. Additionally, porosity in the protected polymer is renewed through acid or thermal de-protection of the tBOC group, providing a unique handle to understand the impact of solution or thermal processing on polymer packing and, as a result, transport.