Initiator-fragment incorporation radical copolymerization of vinyl acetate and 1,2-polybutadiene as a multivinyl monomer

The copolymerization of vinyl acetate (VAc) with 1,2-polybutadiene (1,2-PB; 85.5% 1,2-units and 14.5% 1,4-units) as a multivinyl monomer was carried out at 80 degrees C in dioxane with dimethyl 2,2'-azobisisobutyrate (MAIB) at high concentrations (0.10-0.50 mol/L) as an initiator. The copolymerization of 1,2-PB [0.80 mol/L (monomer unit)] and VAc (1.20 mol/L) with MAIB (0.30 mol/L) for 4 h proceeded homogeneously without gelation to yield a soluble copolymer. The resulting copolymer was divided into methanol- and n-hexane-insoluble parts, of which the yields based on the total weight of the comonomers and initiator were 46 and 20%, respectively. The methanol-insoluble part consisted of the fractions of the 1,2-PB units with (9 mol %) and without (39 mol %) an intact double bond, the 1,4-PB unit (8 mol %), the VAc unit (32 mol %), and the methoxycarbonylpropyl group (12 mol %) as the MAIB fragment, whereas the hexane-insoluble one was composed of the fraction of the 1,2-PB units with (4 mol %) and without (17 mol %) a double bond, the 1,4-PB unit (4 mol %), the VAc unit (60 mol %), and the methoxycarbonylpropyl group (15 mol %). The use of higher concentrations of 1,2-PB and VAc and lower concentrations of MAIB resulted in gelation. The cast film from a chloroform solution of the methanol-insoluble part contained spherical pores organized in a hexagonal way with a monadisperse pore size of 3 mu m. The copolymer molecules seemed to be arranged in an ordered way on the surface layer of the pores, as shown by an optical microscopy image under crossed polarizers. (c) 2006 Wiley Periodicals, Inc.