Theoretical Study of Ethylene−Vinyl Acetate Free-Radical Copolymerization: Reactivity Ratios, Penultimate Effects, and Relative Rates of Chain Transfer to Polymer

Ab initio calculations (UB3LYP/6-31G(d)// UHF/6-31G(d)) and transition state theory on the title polymerization provide relative kinetic information which show the following:  that the hexyl group adequately represents the polymer chain, that theory predicts experimental reactivity ratios with reasonable accuracy, that the penultimate unit effect is small for this copolymerization, that inverted addition to give vicinal diacetoxy units should increase dramatically with polymerization temperature, and that the most favorable short chain branching reaction gives butyl braches as well as 1-acetoxybutyl branches, provided that inverted addition reactions place the acetoxy group six and four carbon atoms from the radical site, respectively. For primary radicals, the absolute values of the computed Arrhenius A factors are believed to be reliable, but the activation enthalpies are about 2 kcal/mol too low, based on a set of calibration reactions used to test the quality of our theoretical methods.