Living radical polymerizations mediated by metallo-radical and organo-transition metal complexes
Journal
ACS Symposium Series
Journal Volume
944
Pages
358-371
Date Issued
2006
Author(s)
Abstract
Cobalt porphyrin derivatives are observed to participate in the control of living radical polymerization (LRP) by two distinctly different mechanisms. Cobalt (II) porphyrin (Co(II)) metallo-radicals mediate a LRP by reacting with polymeric radical (P·) to produce a quasi-equilibrium with an organometallic complex (Co-P) which gives living character through the persistent radical effect. Diamagnetic organocobalt complexes in combination with an additional radical source such as AIBN produces an alternate form of LRP. The rates of polymerization by the organo-cobalt mediated route are relatively fast and approach that of regular radical polymerization because the radical concentration is determined by the organic radical source. The cobalt (II) metallo-radical concentration is vanishingly small in the organo-cobalt mediated process which removes the need for ligands that use large steric requirements to suppress cobalt (II) catalyzed chain transfer. Radical polymerizations of alkyl acrylates, acrylic acid and vinyl acetate mediated by the organo-cobalt porphyrin route are used in illustrating the principal mechanistic features of this process. © 2006 American Chemical Society.
Type
conference paper