Block copolymerization of vinyl ester monomers via RAFT/MADIX under microwave irradiation

Well-defined homopolymers and block copolymers of vinyl esters were synthesized under microwave irradiation via reversible addition-fragmentation chain transfer (RAFT)/macromolecular design via interchange of xanthates (MADIX) polymerization without the significant inhibition or retardation often observed under conventional heating conditions. Poly(vinyl acetate) (PVAc) with molecular weights of 1000−10 000 g/mol was prepared in less than 15 min under microwave irradiation at an apparent temperature of 70 °C in the presence of the commercially available chain transfer agent ethylxanthogenacetic acid. The polymerizations were well-controlled, leading to polymers with narrow molecular weight distributions and excellent agreement between theoretical and experimental number average molecular weights. Despite the high rates of polymerization, the resulting PVAc homopolymers retained a high degree of thiocarbonylthio end group functionality that allowed the synthesis of block copolymers by chain extension with vinyl benzoate and vinyl pivalate. The rates of polymerization during the addition of the second blocks were also high, and the resulting block copolymers were obtained in good yield with excellent blocking efficiencies.