Solvent Effect in the Copolymerization of Ethylene and Vinyl Acetate

The copolymerization of ethylene vinyl acetate (VAc) at 4.0 MPa and 75 °C has been studied experimentally and computationally in four organic solvents, namely, methanol (MeOH), tert-butyl alcohol (TBA), methyl acetate (MA), and dimethyl carbonate (DMC), to reveal the effect of the solvents on copolymerization. The results show a significant dependence of the copolymerization rate and reactivity ratio on the nature of the solvent. Polymerization rate constants decrease in the order of TBA > MeOH > DMC > MA. The results from FTIR spectra and complexation energy calculation suggest that the variance of the copolymerization rate is closely related to the interaction between the monomer and the solvent. A stronger interaction between the monomer and the solvent might decrease the average effective monomer concentration. Various reactivity ratios are interpreted in terms of the stabilization effect of the solvent on electron-deficient species that changes the selectivity of macroradicals. Density functional theory (DFT) calculation performs well in predicting the change in the reactivity ratio in different solvents. The molecular weight of the ethylene vinyl acetate copolymer is remarkably affected by the solvents due to the chain transfer reaction, while the unit sequence is little affected.