3.11 - Organometallic-Mediated Radical Polymerization

Abstract

The term ‘Organometallic-Mediated Radical Polymerization (OMRP)’ encompasses all controlled radical polymerizations that make use of dormant species containing a direct bond between the metal atom and the growing radical chain. There are two versions of such techniques, one resting on the reversible activation of the dormant species by dissociation of the metal–carbon bond (OMRP-RT for ‘reversible termination’) and the other one based on the principle of degenerate transfer, with the growing polymer chain being released by an associative exchange with a second radical (OMRP-DT for ‘degenerative transfer’). The technique has allowed the control of a wide range of monomers from very reactive ones such as AN to vinyl acetate. Transition metals may be involved in a number of other one-electron processes and indeed all of them interplay with OMRP depending on conditions (type and amount of initiator, nature of metal and ligands, coordination number, type of monomer). A general analysis of this interplay is provided in this chapter. In addition to the interplay between dissociative and associative radical exchange processes in the OMRP dormant species, the chain-carrying radical may also interact with the OMRP trapping complex by H• transfer leading to catalytic chain transfer. Finally, transfer of atoms (particularly halogens) may positively or negatively interfere with OMRP. A strategy for the elimination, recovery, and recycling of the metal complex is also discussed.