Copolymerization of vinyl acetate with a homologous series of vinyl esters: A comparative study of vinyl acetate–vinyl ester and ethylene–vinyl ester copolymerization
摘要整理
Abstract The effect of the alkyl group on the relative reactivity of a homologous series of vinyl esters (M 2 ) has been studied with vinyl acetate (M 1 ) as reference monomer and tert ‐butyl alcohol as solvent at 62°C and 35 kg/cm 2 . The description of the relative reactivities of the vinyl esters toward the vinyl acetate (VAc) macroradical in terms of the Taft relation is analogous to our previous findings in a similar study with ethylene (Eth) as reference radical. This implies that chiefly polar factors affect the relative reactivity, whereas from vinyl pivalate (VPV) on steric hindrance impairs the addition rate. The constancy of the r 2 values, also found in the series with Eth (M 1 ) as reference monomer (viz., r 2 = 1.50), appears to exist in the present investigation ( r 2 = 1.04) but does not hold for the VAc–VPV combination. This can be interpreted in terms of steric hindrance. A combination of kinetic results indicates sterically hindered additions in all those reactions in the system Eth–VAc–VPV that involve at least one VPV unit as macroradical or monomer (except for the addition of Eth to a VPV macroradical). The monomer reactivity ratios that pertain to the Eth–VAc–vinyl ester systems are discussed in terms of the Q–e scheme and the product relation postulated by Ham. The Ham relation does not hold for the latter systems.