Michelle Coote

Computer Aided Chemical Design

Media Release

May 2011

Materials Views.

A mechanistic tug-of-war: Initiation via ISET or OSET by Marie-Claire Hermant published: 2011-05-06

The advent of controlled/ living radical polymerization (LRP) techniques, including atom transfer radical polymerization (ATRP) amongst others, has enabled polymer and material scientists to have very fine control over polymer molecular weights, compositions and structures. The mechanistic pathways underlying these techniques have been exhaustively studied, and in many instances, every bump has been ironed out.

This does not however hold for the “spin-off” technique, single electron transfer (SET) LRP first introduced by Percec et al. in 2006. There has been much debate in literature as to whether the outer-electron transfer (OSET) mechanistic route of SET-LRP, the route that has been stated to distinguish it from conventional ATRP, is in fact correct. OSET, in the case of SET-LRP, and inner electron transfer (ISET), in the case of ATRP, describes the cleavage of an alkyl-halide bond that dictates that controlled nature of the polymerization.

This hot debate is continued by the work of Isse et. al who have systematically investigated the nuances of the behaviour of various alkyl-halide initiators (including propagating chain ends). Through quantum-chemical computations and cyclic voltametry, they have investigated the existence of the radical-anion adduct, an essential intermediate to the proposed SET-LRP mechanistic pathway.

Both theory and experiment reveal the absence of any radical-anion adduct implying that the OSET mechanism proposed for SET-LRP should be reconsidered. With such compelling evidence, many researchers now wait with bated breath to see the opposing team’s rebuttal.

Isse et al J. Am. Chem. Soc. 2011 ; DOI: 10.1021/ja110538b