A kinetic description of the free radical polymerization of vinyl acetate in cationic microemulsions

The polymerization of vinyl acetate (VA) in three-component microemulsions stabilized with the cationic surfactant, cetyltrimethylammonium bromide (CTAB), is investigated as a function of concentrations of monomer and initiator (V-50) and temperature. Stable latexes containing small particles (35-50 nm) of poly(vinyl acetate) with average number molar masses of (4-5) x 10(5) g/mol are obtained. Analysis of the molar mass distributions (MMD) indicates that the controlling chain growth termination mechanism is chain transfer to monomer, and not to polymer, which is the dominant; termination mechanism for the emulsion polymerization of this monomer, especially at high conversions. Deconvolution of the MMD curves and measurement of the radius of gyration as a function of molar mass show that more than 80% of the final polymer is linear, produced by chain transfer to monomer, whereas the rest may be branched, probably formed by chain transfer to polymer or by terminal double bond reactions. The population of linear polymer decreases with decreasing reaction temperature, but it is independent of initiator and monomer concentrations.