Mechanism of Cobalt Mediated Radical Polymerization and Its Application in The Direct Synthesis of Conjugated-Unconjugated Block Copolymers
Cobalt mediated radical polymerization (CMRP)1 is famous by controlling the radical polymerization of unconjugated monomers such as vinyl acetate (VAc). Atom transfer radical polymerization (ATRP)2 can control the polymerization of conjugated monomers like methyl methacrylate (MMA) and styrene (Sty). The issue is that the conjugated and unconjugated monomers form the radicals with different stability during the polymerization and thus require different reagents to control the polymerization process. The block copolymers of conjugated and unconjugated monomers were reported to be synthesized by using difunctional initiators or chain-end modification of the first block polymer which require additional synthetic processes and purifications. In our group, we have systematically studied the CMRP and established the mechanism model associated with the thermodynamic and kinetic parameters to correlate the relationship between reduction potential, equilibrium constant of cobalt(II) and organo-cobalt(III), and control mechanism. We also combined CMRP and ATRP to overcome the barrier of the preparation of conjugated-unconjugated block copolymers and obtained the block copolymers of PVAc-b-PMMA and PVAc-b-PSty by a direct chain extension process.3 The linear increased molecular weight and relatively narrow molecular weight distribution observed during the polymerization of both blocks demonstrated that the polymeric products were formed under a well controlled process.
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