Owing to their high surface area and hierarchical porosity, microporous polymers, such as polymers of intrinsic microporosity (PIMs), have shown great potential in heterogeneous catalysis, adsorption, and membrane separations, among other applications. Linear microporous polymers (e.g., solution-processable PIM-1), can be easily manufactured into form factors consistent with large-scale separations (e.g., hollow fibers). However, linear microporous polymers can be dissolved, swollen, or plasticized by various solvents, which restricts their application in aggressive operating environments. Two of the most prominent post-fabrication methods for improving the stability of polymers are pyrolytic carbonization and crosslinking. These are both promising approaches to rigidifying polymeric materials, but require a near-complete transformation of the precursor in the former case and chemical/thermal treatments in the latter case.<br/>Here, we develop a novel post-fabrication modification technique for improving the stability of microporous polymers without damaging the microstructure and macroscale form factors. Cyclic vapor phase infiltration of metal-organic precursors and water into the structure of PIM-1 creates monolayers or bilayers of sub-nanometer metal oxide structures on the surfaces of the interconnected PIM-1 micropores. The resulting interpenetrating atomic-scale networks of metal oxide and PIM-1 retain the microporosity and exhibit excellent solvent resistance to strong solvents for PIM-1 (chloroform, dichloromethane, and tetrahydrofuran). While PIM-1 membranes cannot effectively reject polystyrene oligomers below 1200 g/mol from ethanol, the hybrid PIM-1 membranes reject polystyrene oligomers larger than 400 g/mol. Besides, the interpenetrating aluminum oxide networks inhibit the interaction between membranes and solutes, increasing the Rose Bengal rejection from 45% to 86%. Since the vapor phase infiltration process can be directly applied to state-of-art membrane modules, this treatment has the potential to be adopted into the large-scale manufacturing of advanced membranes.

Vapor-phase infiltration of metal oxides into microporous polymers for solvent stable nanofiltration membranes

2019 Spring National Meeting

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