Microporous carbon materials with finely tuned pore sizes can be made from hyper-branched polymers.

Porous carbons have a wide variety of potential and current applications, including in gas separation and absorption, and as catalyst supports. But current methods to make these materials, such as template synthesis or carbonisation of polymer blends, do not allow control of the pore distribution.

Norifumi Kobayashi and Masashi Kijima of the University of Tsukuba, Japan, have developed a new way to make porous carbons, which allows more control over the development of the pores. The researchers started by making hyper-branched polymers in which rigid cyclic components, such as benzene rings, are linked together by alkyl chains consisting of carbon-carbon single bonds. 

The rigid components are much more thermally stable than the alkyl chains, so when the researchers heated the polymers to 450 °C only the alkyl groups degraded. This left behind a rigid polymer network containing permanent pores where the alkyl groups once were.  

Heating this material to even higher temperatures of around 900 °C formed a microporous carbon material with finer pores. Kijima terms the new materials 'porous organoceramics'.

John Plater, an organic chemist at the University of Aberdeen, UK, was impressed by the work, saying, 'it opens up a new field of research aimed at the discovery of new functional materials with tailored properties.'