title: Electronic and steric ligand effects in the radical polymerization of vinyl acetate mediated by beta-ketoiminate complexes of cobalt(II).
abstract: Complexes Co[OC(Ph)CHC(Me)NAr](2) [Ar=Ph, 1; o,o'-C(6)H(3)Me(2) (Xyl), 2; p-C(6)H(4)CF(3), 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30 degrees C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M(n) values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2>1>3. Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V-70/1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(beta-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.
authors.affiliation: Laboratoire de Chimie des Polymères Organiques, ENSCPB-CNRS-Université Bordeaux 1, 16, Avenue Pey Berland, 33607 Pessac Cedex, France.
authors.forename: K S
authors.initials: KS
authors.lastname: Santhosh Kumar
authors.forename: Yugang
authors.initials: Y
authors.lastname: Li
authors.forename: Yves
authors.initials: Y
authors.lastname: Gnanou
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baisch
authors.forename: Yohan
authors.initials: Y
authors.lastname: Champouret
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Poli
authors.forename: Kiyoshi C D
authors.initials: KC
authors.lastname: Robson
authors.forename: W Stephen
authors.initials: WS
authors.lastname: McNeil