Switching off polymerisation in the dark

With summer in full swing, the world of polymer science is about to get a boost following news that sunlight can kick-start living polymerisation reactions.

Ian Manners’ team at the University of Toronto, Canada, has developed a method to polymerise silicon-bridged ferrocenophanes. The process can be initiated by photoirradiation from a mercury lamp, or even bright sunlight. But in what Manners describes as a ’remarkable’ twist, the reaction stops in the dark.

In living polymerisations, the end chain of the polymer is altered so it doesn’t have the ability to stop growing through a conventional chain termination step. The rate of initiation of the chain polymerisation reaction is faster than the rate of propagation of the chain reaction. The effect is a steady, controlled polymerisation, with all resulting polymer chains ending up about the same length. The resulting metal-containing polymers show promise in a number of high-tech applications: recently a ruthenium polymer was used in a sensor to monitor air-pressure on aircraft wings.

The light-initiated method developed by Manners, now based at the University of Bristol, UK, can control the growth of block copolymers when the light is switched on and off. ’In traditional living anionic polymerisations, the monomer is activated by heat, and basic anionic initiators such as butyllithium are necessary. Unfortunately, the highly basic initiators often cause side reactions with many monomers, especially metal-containing monomers. Compared to heat, light provides bond-specific activation and is therefore much more efficient,’ Manners told Chemistry World. An added benefit is the wide range of monomers the method can be applied to, and the generality of the technique, Manners claims.

Rachel O’Reilly, a polymer chemist from the University of Cambridge, UK, said this wide-ranging applicability is the key innovation. ’Using photo activation allows for the polymerisation of functional monomers with reactive groups which are incompatible with conventional anionic ring opening polymerisation techniques,’ she told Chemistry World. ’The development of any new living polymerisation techniques is exciting, especially this one given its versatility in the synthesis of functionalised polymers,’ she said.

Katharine Sanderson