Synthesis and Characterization of Poly(vinyl acetate)-b-poly(dimethylsiloxane) Diblock Copolymer by Iodine Transfer Radical Polymerization

Iodine transfer radical polymerization as an easy, efficient and robust method of controlled radical polymerization has been applied for a wide range of monomers. This polymerization technique is used in both homogeneous and heterogeneous processes. Iodine transfer radical bulk polymerization of the vinyl acetate (VAc) monomer was carried out in the presence of 2,2'-azobis(isobutyronitrile) (AIBN) as an initiator and ω-iodine-terminated poly(dimethyl siloxane) (PDMS-I) as a macrotransfer agent at 80oC. PDMS-I with a number average molecular weight of 5029 g/mol and a polydispersity index of 1.23 was synthesized by bromination followed via iodination of the ω-hydroxyl-terminated poly(dimethyl siloxane) (PDMS-OH). The product was used as a macrotransfer agent in the iodine transfer radical polymerization of VAc. Formation of the poly(vinyl acetate)-b-poly(dimethyl siloxane) diblock copolymer with a number average molecular weight of 19620 g/mol and a polydispersity index of 1.53 was proved by proton-nuclear magnetic resonance spectroscopy and gel permeation chromatography. A good agreement between the theoretical and experimental molecular weight calculated by proton-nuclear magnetic resonance spectroscopy and gel permeation chromatography was achieved, indicating that the PDMS-I macrotransfer agent was completely consumed and the PDMS impurities did not participate in the polymerization reaction. The analysis of the chain-ends was performed by using proton-nuclear magnetic resonance spectroscopy technique. It was found that a considerable number of inverse chain-ends were present at the end of the polymerization. Moreover, formation of several other side products due to degradation of the functional chain-ends was confirmed.