Effect of Head-To-Head Addition on Vinyl Acetate Propagation Kinetics in Radical Polymerization

The radical propagation kinetics of vinyl acetate (VAc) has been studied by pulsed-laser polymerization coupled with analysis of the resulting polymer molar mass distributions. The significant increase in the apparent propagation rate coefficient observed with increasing pulse repetition rate is explained by the influence of the head-to-head defects formed during chain growth. Simulations that include head-to-head monomer addition are combined with an analysis of the experimental results to estimate the subsequent rate coefficients for reaction of the resultant radical as well as the propagation rate coefficient of normal head-to-tail addition. An analytical expression is derived for an averaged rate coefficient, kpav, for the system, with the best-fit Arrhenius parameters of ln(A/L mol(-1) s(-1)) = 16.56 +/- 0.35 and E/R= 2508 +/- 108 K.