Oxygen-ascorbic acid-vanadyl ion initiating system. A kinetic study of the polymerization of methyl methacrylate and acrylonitrile in aqueous sulfuric acid

Abstract

The polymerization of methyl methacrylate (MMA) and acrylonitrile (AN) initiated by the oxygen-ascorbic acid (AA)-vanadyl ion (VO²⁺) system was studied at 40°C in dilute sulfuric acid medium. The rate of polymerization, R^p, was followed gravimetrically and found to be proportional to [MMA]^1.3, [O₂]^0.6, and [VO²⁺]° at [VO²⁺]=4−8×10⁻⁴ M̲ in the polymerization of MMA. In the polymerization of AN, R was dependent on [AN]^1.5, [O₂]^0.5, and [VO²⁺]° at[VO²⁺]=4−10×10⁻⁴ M̲, while at [VO²⁺]>10⁻³ M̲ it was proportional to [AN]^1.7, [O₂]^0.7, and [VO²⁺]^0.6. A slight dependence of R_p on [AA] and [H₂SO₄] was observed in both polymerizations. An increase of ionic strength had an accelerating effect on R_p. An initial increase in R_p and then a decrease with temperature was noticed. A plausible reaction mechanism with initiation by the primary radical R produced from the dissociation of the O₂-AA-VO²⁺ complex and termination by mutual interaction with predominant oxidation of R by VO²⁺ was found to be consistent for the observed kinetic results at all [VO²⁺] for MMA and for AN at low [VO²⁺]. Linear termination was found to be operative at high [VO²⁺] in the polymerization of AN. The chain length of the polymers was determined viscometrically.