EFFECTS DUE TO PREFERENTIAL SORPTION OF M ONOMERS IN COPOLYMERIZATIONTO HIGH CONVERSIONS

In copolymerization of styrene with acrylonitrile and vinylpyrrolidone with vinyl acetate at moderate and high conversions, the ratio betwee n the rates of monomer depletion is controlled by the concentration of initiator. In some cases, plots of current monomer feed composition v ersus conversion may be described in terms of effective reactivity rat ios r(1) and r(2) determined at low conversions. The composition distr ibution for styrene-methacrylic acid copolymer at 30, 50, and 70% conv ersions is significantly broader than that expected on assumption that conversion is the only factor giving rise to copolymer heterogeneity. At 15 and 50% conversions, the data on composition and molecular mass es of the copolymer fractions are related by a general relationship si milar to that established previously for the copolymers obtained at lo w conversions. The effects discovered are explained by preferential so rption of the monomers. A model treating preferential sorption in copo lymerization to high conversions is discussed.