| Summary: | Over the past forty years, membrane-based gas separations have emerged as a promising alternative to energy-intensive separation processes such as amine absorption and cryogenic distillation. However, a trade-off between permeability and selectivity as well as issues of decreased performance at high pressures have hindered widespread membrane deployment. In response, there is a growing body of research aimed to developing materials formulations that address these polymer-specific disadvantages. Polymers of intrinsic microporosity (PIMs) were designed as ultrahigh-free-volume materials with inefficient chain packing and high surface areas, resulting in pure-gas performance beyond that of traditional glassy polymers. Hybrid systems such as mixed-matrix membranes (MMMs) also emerged as a means of increasing overall separation performance and reducing plasticization. Despite the surge in available material platforms for membrane-based separations, the performance and fundamental underpinnings of binary and ternary mixed-gas transport in these microporous polymers and MMMs remains underexplored.
This thesis combines synthetic chemistry, materials science, and chemical engineering to develop a platform of functionalized PIM derivatives and to investigate their pure- and mixed-gas transport properties in industrially relevant conditions. Approaches to increase diffusion-based performance in PIMs are developed, including methods to functionalize PIMs with carboxylic acid and amine functionalities, template free volume elements through protection/de-protection chemistries, and fabricate MOF–polymer composites. The effects of polymer functionalization, free volume manipulation, and membrane hybridization on transport are investigated via pure-gas testing and sorption–diffusion analysis, to elucidate structure–property relationships between polymer packing structure and gas diffusion. Polymers with identical backbone structures and varying backbone functionality are subsequently used as a platform to investigate the effects of CO₂ sorption affinity on the binary and ternary mixed-gas transport. Among the PIMs considered, amine-functionalized PIM-1 shows a notable increase in mixed-gas selectivity compared to the pure-gas case. The generalizability of this approach is investigated through aminefunctionalization of a different family of polymers, poly(aryl ether)s (PAEs). Results indicate that amine-functionalization can serve as a promising route to increase mixed-gas transport performance while also reducing CO₂-based plasticization. The influence of CO₂ sorption affinity on transport is finally investigated through ternary mixed-gas tests in toxic gas mixtures containing H₂S. Taken together, this thesis derives connections between macromolecular chemistry and complex gas transport performance in PIMs. By developing these structure-property-performance relationships, this work provides context for the potential of PIMs in industrial applications and rational design handles for future development of high-performing membrane solutions.
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