Effect of solvent on the copolymerization of ethylene and vinyl acetate

The ethylene (M 1 )–vinyl acetate (M 2 ) copolymerization at 62°C and 35 kg/cm 2 with α,α′‐azo‐bisisobutyronitrile as initiator has been studied in four different solvents, viz., tert ‐butyl alcohol, isopropyl alcohol, benzene, and N , N ‐dimethylformamide. The experimental method used was based on frequent measurement of the composition of the reaction mixture throughout the copolymerization reaction by means of quantitative gas chromatographic analysis. Highly accurate monomer reactivity ratios have been calculated by means of the curve‐fitting I procedure. The observed dependence of the r values on the nature of the solvent is surprisingly large and can be correlated with the volume changes (= excess volumes) observed on mixing vinyl acetate (VAc) with the relevant solvent. An increased hydrogen bonding or dipole–dipole interaction through the carbonyl moiety of the acetate side group of VAc, induces a decreased electron density on the vinyl group of VAc, which in turn leads to a decreased VAc reactivity. The differences among the overall rates of copolymerization in the various solvents can be interpreted in terms of a variable chain transfer to solvent and the rate of the subsequent reinitiation by the solvent radical. In the case of benzene, complex formation is believed to play an important part.