Kinetics, Thermodynamics, and Monomer Reactivities in Radical Polymerization of α-Acetoxystyrene

The radical polymerization behavior of α-acetoxystyrene (ACOST) was investigated in toluene, using α,α'-azobis(isobutyronitrile) (AIBN) as the initiator. The polymerization of ACOST is an equilibrium process with a ceiling temperature (Tc) of 47°C at 1 mol/L of monomer due to the steric hindrance. The rate of polymerization (Rp) can be expressed by Rp=k[AIBN]0.45([M]-[M]e)1.0, considering the depolymerization process with an equilibrium monomer concentration of [M]e. The overall activation energy has been determined to be 116 kJ/mol. The enthalpy of polymerization and entropy of polymerization obtained from a linear relationship between In [M]e and l/T are -26.5 kJ/mol and -82.6 J/(K.mol), respectively. The Tc is low because of the low ΔHp but high enough to allow radical homopolymerization owing to the low ΔSp, which is significantly lower than the typical values (-100 to -125 J/(K-mol)) for vinyl monomers. Monomer reactivity ratios of bulk copolymerization of ACOST (M2) with methyl methacrylate (MMA, M1) are r1 = 0.644 and r2 = 0.754, respectively, at 60°C. The temperature dependence (50-80°C) of the reactivity ratios has revealed that the copolymerization mechanism can be adequately described by the Mayo-Lewis model; a depolymerization process does not have to be taken into consideration in copolymerization. Q and e values of ACOST can be calculated as 0.82 and -0.45 from the reactivity ratios. Although the values seem to be reasonable, the serious steric effect makes their meaning obscure. © 1990, American Chemical Society. All rights reserved.