Effect of preferential solvation in the radical copolymerization of vinyl acetate with N-vinylpyrrolidone and styrene with methacrylic acid in bulk and solution

It was demonstrated that, in the copolymerization in bulk and in a solution of n-butyl alcohol, the composition of vinyl acetate copolymer with N-vinylpyrrolidone depends on the concentration of AIBN. A variation in the copolymer composition agrees with the dependence of the coefficients of the preferential solvation of the copolymer macromolecules on their molecular mass. A copolymer synthesized by the solution copolymerization and isolated at the initial stage of the process is characterized by a wide distribution with respect to composition. When copolymerization is performed in n-butyl alcohol, r(1)<1, r(2)<1, and the r(1)r(2) product is significantly smaller compared to the bulk copolymerization. This fact suggests an enhanced tendency toward alternation of the monomer units. In the copolymerization of styrene with methacrylic acid in dioxane, unlike bulk copolymerization, the copolymer composition is independent of the molecular mass; the copolymer isolated at a small conversion has a narrow composition distribution. Using the film Langmuir balance, it was shown that the surface pressure isotherms of the monomolecular layers of the styrene-methacrylic acid copolymer synthesized in bulk and in dioxane appreciably differ when water with pH 10 is used as a support. The observed differences are explained by the wide composition distribution of the copolymers prepared by the bulk copolymerization and isolated at low conversions and by the narrow distribution in the case of solution copolymerization.