Control of Radical Polymerizations by Metalloradicals

摘要

Cobalt(II) porphyrin complexes ((por)Co~II centre dot) are used to illustrate how metalloradicals (M centre dot) can function to control radical polymerization through both chain transfer catalysis and living polymerization. Chain transfer catalysis (CTC) is best achieved when there are minimal steric demands. This allows #beta#-hydrogen abstraction from oligomer radicals by M centre dot, as illustrated by the readical polymerization of methyl methacrylate in the presence of tetraanisylporphyrinato cobalt(II). When #beta#-H abstraction fro mthe oligomer radical is precluded by sterics, then a metalloradical mediated living radical polymerization (LRP) can occur. Radical polymerization initiated and mediated by organo-cobalt tetramesitylporphyrin complexes manifest high living character as shwn be the linear increase in M_n with conversion, formation of block copolymers and relativity low polydispersity homo and block copolymers. Kinetic studies provide rate and activation parameters for the living radical polymerization process.