Thermodynamics of copolymerization of vinyl acetate and vinyl pivalate

Vinyl pivalate (VPi) and vinyl acetate (VAc) were copolymerized at low temperature using 2,2′-azobis(2,4-dimethylvaleronitrile) as an initiator. Copoly(VPi/VAc) was prepared in a broad range of chemical composition, from 0/10 to 10/0 of VPi/VAc molar feed ratio. A statistical treatment of the 1H NMR peak intensities brought to the determination of the reactivity ratios of the comonomers. A thermodynamic study of the molecular dynamics simulation data led to the estimation of number-average sequence lengths of comonomers and Gibbs free energy change over VPi content. From this result, the retardation of copolymerization rate at about 5/5 composition was also explained. Enthalpies of –VAc–VPi∗, –VPi–VAc∗, and –VPi–VPi∗ formation were calculated as −12.07, −5.57, and −18.33 kcal/mol, respectively.