Microporous materials can be derived directly from soluble polymers whose randomly contorted shapes prevent an efficient packing of the macromolecules in the solid state.

A polymer with a rigid, randomly contorted molecular structure (see Figure), incorporating fused rings connected by spiro‐centres, may be precipitated or cast from solution to give microporous powders and membranes stable up to temperatures of 350 °C, with apparent surface areas > 600 m2 g–1. Organophilic membranes may be formed, as demonstrated by the separation of phenol from water by pervaporation.

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Novel types of microporous material are required for chemoselective adsorptions, separations and heterogeneous catalysis. This concept article describes recent research directed towards the synthesis of polymeric materials that possess microporosity that is intrinsic to their molecular structures. These polymers (PIMs) can exhibit analogous behaviour to that of conventional microporous materials, but, in addition, may be processed into convenient forms for use as membranes. The excellent performance of these membranes for gas separation and pervaporation illustrates the unique character of PIMs and suggests immediate technological applications.