Preparation of block copolymers from macroradicals in viscous homogeneous heterogeneous systems
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Abstract
Living macroradicals of styrene and vinyl acetate were prepared in viscous good and poor solvents. It was found that when these macroradicals were heated with a second vinyl monomer, block copolymers were produced. Exceptional rates of polymerization and yields of block copolymers were obtained in viscous poor solvents. The small microparticles, formed when styrene and vinyl acetate were polymerized in a poor solvent, were counted and measured by scanning electron microscopy. The number of particles was found to be linearly related to the initiator concentration. The size of the particles is related to the nature of the polymer and diluent and their solubility parameter. The size of the particles was found to be independent of the diluent viscosity and initiator concentration. It was postulated that each particle may contain a single macroradical. Block copolymers of styrene and methyl methacrylate, acrylic acid, ethyl methacrylate, acrylonitrile, and vinyl acetate were prepared from styrene macroradicals. Block copolymers of vinyl acetate and methyl methacrylate, acrylic acid, vinyl pyrrolidone, acrylonitrile, and styrene were prepared from vinyl acetate macroradicals. The block copolymers were characterized by yield, solvent fractionation, pyrolysis gas chromatography, and differential scanning calorimetry.