A Kinetic Description of the Free Radical Polymerization of Vinyl Acetate in Cationic Microemulsions

Abstract

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) × 105 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.

Surfactant concentration effects on the microemulsion polymerization of vinyl acetate

“…Table 2 reports M w and the polydispersity indexes (ðI D Z M w = M n Þ as a function of conversion for the CTAB/water ratio of 5/95 and shows that both M w and I D increase as reaction proceeds. The poly(vinyl acetate) average molar masses obtained in this work and in other microemulsion systems previously reported by us [3,6,15,19] are much lower than that reported in the polymerization of this monomer in an emulsion stabilized with CTAB in a surfactant/water ratio of 1/99 (Table 1) [20] and those reported elsewhere [4,5]. Fig.…”

Emulsion Polymerization

“…The final polymer particles generally have diameters of 10-50 nm. Although many of the characteristics of microemulsion polymerization parallel those of emulsion polymerization, the details are not exactly the same de Vries et al, 2001;Lopez et al, 2000;Medizabial et al, 2000]. Water-soluble initiators are commonly used, but there are many reports of microemulsion polymerization with oil-soluble initiators.…”

Kinetics and monomer partitioning during polymerization of vinyl acetate in microemulsions stabilized with AOT and n-butanol

“…However, because of chain transfer reactions to polymer at high conversions during the emulsion polymerization of VAc, highly branched polymers are obtained [5][6][7][8]. On the other hand, in batch microemulsion polymerization of VAc in threecomponent cationic or anionic microemulsions chain transfer reactions to monomer control chain termination, even at high conversions, in contrast to emulsion polymerization [9][10][11].…”