Transition metal catalysts for controlled radical polymerization

The discovery, in the mid 1990s, that certain cobalt, ruthenium and copper complexes could effectively control the radical polymerization of a number of polar olefins, allowing for the facile synthesis of complex macromolecular architectures, fostered an intense search for increasingly better performing catalysts. As a consequence, several metal complexes were designed and tested. This article presents an organized and detailed overview of the most significant developments in the use of transition metal compounds to initiate, mediate and control radical polymerization, i.e., atom transfer radical polymerization or organometallic mediated radical polymerization. The catalysts have been classified according to the group of the periodic table to which the relative metal centers belong. Their catalytic performance, the mechanism with which they are supposed to operate, the structure-reactivity correlations as well as the type of monomers and experimental conditions employed are described. The use and the role of non-transition metal complexes in controlled radical polymerization are also discussed.