Owing to their high surface area and solution-processability, polymers of intrinsic microporosity (PIMs) have shown great potential in heterogeneous catalysis, adsorption, and membrane separations, among other applications. However, the limited organic solvent resistance of PIM-1 restricts its application in aggressive operating environments. Two of the most prominent post-fabrication methods for improving stability of polymers are pyrolytic carbonization and crosslinking. These are both promising approaches to rigidifying polymeric materials, but require near-complete transformation of the precursor in the former case, and chemical/thermal treatments that result in partial conversion of the precursor in the latter case. Here, we discuss a new technique for improving the stability of polymers of intrinsic microporosity (PIMs) while retaining essentially the same microstructure as the precursor polymer. Cyclic vapor phase infiltration of atomic layer deposition (VPI-ALD) precursors (e.g., water and metal precursors) into the structure of PIM-1 (a prototypical PIM) results in the growth of sub-nanometer metal oxide structures on the surfaces of the interconnected PIM-1 micropores. The resulting oxide-PIM-1 hybrid material maintains the microporosity of PIM-1, and the pore size and pore volume are observed to decrease after additional VPI-ALD cycles. The hybrid materials exhibit excellent solvent resistance to strong solvents for PIM-1 (chloroform, dichloromethane and tetrahydrofuran). The rejection of dye molecules (dissolved in ethanol) from hybrid membranes in hollow fiber format increased markedly from those observed for neat PIM-1: the rejection of Oil Red, Solvent Blue 38 and Rose Bengal rose from 93%, 92% and 28% to 98%, 99% and 80%, respectively.

Improving the stability of PIM-1 via vapor phase infiltration - atomic layer deposition (VPI-ALD)

256th National Meeting (2018)

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