University of Connecticut |
Polymer Program SeminarPathways for Transition Metal Controlled Radical Polymerization Friday, October 14, 2005 11:00 am , IMS Room 20 Cobalt(II) metal-centered radicals and related organo-cobalt derivative will be used to illustrate the control of radical polymerization through catalytic chain transfer (CCT) and living radical polymerization (LRP) . Alkene terminated macromonomers result from CCT and low polydispersity homo-polymers and block copolymers are prepared by LRP . Emphasis will be placed on describing a new form of organometallic degenerative transfer (DT) living radical polymerization process that is useful in forming amphiphilic block copolymers . Organo-cobalt porphyrin complexes in combination with azo radical sources are observed to mediate controlled / living radical polymerization of acrylates and vinylesters through a degenerative transfer pathway called radical interchange polymerization (RIP). Organo-cobalt complexes are used to illustrate the most prominent mechanistic features of the RIP process. Comparative studies will be presented for alternate approaches to obtain living radical polymerization by metallo-radical mediated reversible termination (RT) and through organo-metal mediated degenerative transfer (RIP) processes. Slow polymerization rates and chain transfer by b-H abstraction that are associated with a metallo-radical mediated reversible termination (RT) are largely circumvented by the organo-cobalt mediated process which suppresses the metallo-radical concentration. Kinetic-mechanistic studies reveal that both associative and dissociative routes can be responsible for interchange of radicals between solution and dormant organo-metal complexes depending on the choice of monomers, organo-metal catalyst and reaction conditions. The scope of both catalyst materials and applicable monomers are substantially larger for the RIP process compared to RT. Extensions of radical interchange polymerization to new classes of olefin monomers and block copolymers will be presented.
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