Click Chemistry

Creating polymers with controlled length and stereo chemistry is an area where nature is currently streets ahead of science. But researchers at Massachusetts Institute of Technology (MIT) in the US have come closer to closing the gap, with an efficient strategy that allows them to synthesise a new family of uni molecular, sequence- and stereo-defined polymers using click chemistry.

Similar polymers have been created by adding one monomer at a time to a growing chain attached to a solid or soluble polymer support, but limited yields and inefficient use of reagents can result.

'We utilize an iterative exponential growth strategy where instead of adding one monomer at a time we double the length of the polymer with each iteration,' explains senior author Jeremiah A Johnson. 'It leads to longer chains of repeating sequences in fewer steps than would be possible with other methods, and also enables the use of catalytic reactions that are more atom economical.'

The strategy has produced macromolecules with exact chain lengths before. Johnson's new system - exponential growth plus side-chain functionalisation, or IEG+ - is exceptional in that one of the deprotection steps also includes the addition of a variable side chain.