Journal of Polymer Science Part A: Polymer Chemistry, Vol.37, No.5, 589-601, 1999
Effect of solvent on the rate constants in solution polymerization. Part II. Vinyl acetate
Measurements were made of the value of the lumped kinetic constant k(p)/k(t)(0.5) of vinyl acetate in different solvents and with different initiators. This quantity was evaluated using the well-known conversion vs, time approach in dilute solutions using both azo-bis-isobutyronitrile and benzoyl peroxide (AIBN and BPO), and two different solvents (toluene and ethyl acetate) at 60 degrees C. As was found for butyl acrylate in Part 1 of this series, it was found that the value of the lumped rate constant depends very strongly on the concentration of monomer in solution, decreasing as the solution becomes more and more dilute. However, unlike butyl acrylate, vinyl acetate is much more susceptible to changes in the solvent type, with toluene acting as a severe retarding agent of polymerization. The results of the present study suggest that at least two separate effects of solvent exist simultaneously in the case of vinyl acetate polymerization, and that both of them must be taken into account when attempting to model this type of system. The number- and weight-average molecular weights of the different polymers were also measured, and excellent agreement was found between the measurements and model predictions. A linear relationship was shown to exist between the value of the lumped constant and the square root of the number-average chain length.