Long branching in poly(vinyl acetate) and poly(vinyl alcohol). III. Kinetic study of the branching reaction in the radical polymerization of vinyl acetate

Abstract

AbstractThe branching reaction in the radical polymerization of vinyl acetate was studied kinetically. Branching occurs by polymer transfer as well as terminal double‐bond copolymerization. The chain‐transfer constants to the main chain (Cp,2) and to the acetoxy methyl group (Cp,1) on the polymer were calculated on the basis of the experimental data described in the preceding paper giving Cp,2 = 3.03 × 10−4, Cp,1 = 1.27 × 10−4 at 60°C, and Cp,2 = 2.48 × 10−4, Cp,1 = 0.52 × 10−4 at 0°C. Chain transfer to monomer is important with respect to the formation of the terminal double bond. The total values of transfer constants to the α‐ or β‐position in the vinyl group and the acetoxymethyl group in vinyl acetate was determined to be 2.15 × 10−4 at 60°C. The transfer constant to the acetyl group in the monomer (Cm,1) was also evaluated to be 2.26 × 10−4 at 60°C from the quantitative determination of the carboxyl terminals in PVA. These facts suggest that the chain‐transfer constant to the α‐ or β‐position in the monomer (Cm,2) is nearly equal to zero within experimental error. Copolymerization reactivity parameters of the terminal double bond were also estimated. In conclusion, it has become clear that the formation of nonhydrolyzable branching by the terminal double‐bond reaction can be almost neglected, and hence that the long branching in PVA is formed only by the polymer transfer mechanism. On the other hand, a large number of hydrolyzable branches in PVAc are prepared by the terminal double‐bond reaction rather than by polymer transfer.