Hierarchically porous polystyrene membranes fabricated via a CO2-expanded liquid selective swelling and in situ hyper-cross-linking method

Abstract

Hierarchically porous polymeric materials represent a new class of materials that have attracted both industrial and academic interest. This paper presents a novel, etching-free and versatile preparation methodology, using commercially available polystyrene and a CO₂-expanded liquid selective swelling process combined with a hyper-cross-linking reaction. The morphology of the membranes was observed with electron microscopes, and the chemical structure of the membranes was investigated using Fourier transform infrared spectrometry and solid-state nuclear magnetic resonance measurements. One level of macroporous structures was produced by a CO₂-expanded methanol selective swelling process, while the other level of micropores was created via the hyper-cross-linking reaction. The cross-linked membranes possessed large specific surface areas and excellent thermal stability, and have potential applications in catalysis, separation and gas storage.