RIGID POLYMERS PACKED WITH PORES

A family of polymers riddled with nanosized pores could be used in separation and adsorption processes and in heterogeneous catalysis, according to the chemists in England who developed the materials. Dubbed "polymers of intrinsic microporosity" (PIMs), they are synthesized from commercially available starting materials.

The work was carried out by reader in chemistry Neil B. McKeown, senior lecturer in chemistry Peter M. Budd, and coworkers at the University of Manchester [Chem. Commun., 2004, 230].

"The microporosity originates from the highly rigid and contorted molecular structures of the polymers, which prohibit close packing of the macromolecules in the solid state," McKeown tells C&EN. "The presence of interconnected micropores with an average diameter of 0.5 nm results in remarkably high surface areas."

Unlike conventional microporous materials--zeolites or activated carbons, for example--PIMs are soluble and can be cast into thermally stable films suitable for use as separation or reactive membranes.

"The solubility also allows a PIM to be used as a microporous matrix for the support of a homogeneous catalyst simply by casting a solution containing both polymer and catalyst, thereby entrapping the catalyst within its micropore structure," McKeown says. "The nature of the accessible surface is determined by the choice of the monomer precursors. Bespoke [custom-made] PIMs can therefore be prepared for chemoselective catalysis, separation, or adsorption, and it will be possible to introduce chirality for enantiomeric processes."

The Manchester chemists have shown that PIMs can be fabricated into robust, freestanding films that can be used as membranes for removing organic compounds like phenol from water. The group is also planning to investigate the use of PIMs as selective adsorbents for toxic and malodorous compounds.