Aqueous polymerization of methacrylamide initiated by KMnO4/H2C2O4 redox system

The polymerization of methacrylamide initiated by potassium permanganate/oxalic acid redox system has been studied at 35 ± 0.2°C in a nitrogen atmosphere. The rate of polymerization is independent of the activator (oxalic acid) concentration within the range 5·10^?3 to 10·10^?3 mole·1^?1, except at very high (above 10·10^?3 mole·1^?1) or at very low (below 5·10^?3 mole·1^?1) concentrations of the activator. The rate varies linearly at low monomer concentration (up to 5.87·10^?2 mole·1^?1). The catalyst exponent decreases from nearly unity (0.91) to 0.66 with increase in concentration of the catalyst (KMnO₄) probably due to participation of primary radicals in the termination of the growing chain. The addition of strong acid (H₂SO₄) within the range 5 · 10^?4–15 · 10^?4 mole · l^?1, shows a constant pH of 2.7 resulting in no change in initial rate. With activator alone (H₂C₂O₄ · 2H₂O), within the pH range 2.7 to 2.9 an optimum is observed. The initial rate increases with increase in polymerization temperature. The overall energy of activation as calculated from the ARRHENIUS plot has been found to be 15.1 kcal · mole^?1 within the temperature range 30–50°C. Organic solvents (water miscible only) depress the initial rate and the maximum conversion. Small amounts of neutral salts (KCl and Na₂SO₄), however, show no appreciable effect on the polymerization rate, but small amounts of manganous salts (MnSO₄) can increase the initial rate to a considerable extent. High concentrations of MnSO₄ result in termination of the growing chain. A complexing agent, Na₂F₂, decreases the initial rate but increases the maximum conversion. Introduction of fresh catalyst at intermediate stages of polymerization increases both the rate of the reaction and the conversion.