Redox polymerization of 2-hydroxyethyl methacrylate, 2: Kinetics, mechanism and solvent effect using manganese triacetate/cyanoacetic acid as the redox system

Polymerization of 2-hydroxyethyl methacrylate (HEMA) initiated by the redox system manganese triacetate (Mn(III)/cyanoacetic acid (CAA) was investigated kinetically in DMF and in HOAc/water (80:20 v/v). Monomer (M) conversion was followed gravimetrically. Polymerization was carried out at 31°C and at 41°C. The rate of polymerization Rp in DMF is expressed by the equation, Rp ∝ [M]1,4 [Mn(III)]0,4 [CAA]0,4. In HOAc/water, the polymerization exhibited a strong dependence on the concentration of Mn(III). That is, at low concentrations of Mn(III), the rate variations are [M]1,0, [CAA]0,5 and [Mn(III)]0,5, while at high Mn(III) concentration the polymerization rates are independent of [Mn(III)] and vary as a function of [M]1,5 and [CAA]0,5. Enhanced oxidation of the primary radicals by Mn(III) at higher concentrations has been elicited to explain the observed orders. The degree of polymerization was found to increase with increase in concentrations of monomer and decrease in concentrations of CAA and Mn(III). The polymerization rates as well as the molecular weights of the polymers are higher in HOAc/water than in DMF. The enhanced polymerization rates have been attributed to the increased propagation and the reduced termination rates.