Aqueous polymerization of methacrylamide initiated by the redox system K₂S₂O₈/ascorbic acid

Abstract

Abstract The polymerization of methacrylamide initiated by the redox system K 2 S 2 O 8 /ascorbic acid has been studied at 35 ± 0,2°C under the influence of atmospheric oxygen. The molecular oxygen autocatalyses the polymerization rate. The rate of polymerization is independent of the activator (ascorbic acid) concentration within the range 2,83 · 10 −3 to 11,3 · 10 −3 mol · l −1 , this does not hold below or above the given concentration range. The rate varies linearly at low monomer concentration (up to 17,76 · 10 −2 mol · l −1 ). The catalyst exponent decreases from nearly unity (0,94) to 0,57 with increasing concentration of the catalyst probably due to participation of primary radicals in the termination of growing chain. The initial rate is not changed by the addition of a strong acid (H 2 SO 4 ) within the range 15 · 10 −5 to 30 · 10 −5 mol · l −1 . With the activator (ascorbic acid) alone, an optimum is observed within the pH range 2,9–3,5. The initial rate and the limiting conversion increases with increasing polymerization temperature. The overall energy of activation as calculated from the ARRHENIUS plot has been found to be 16,0 kcal.mol −1 within the temperature range 30–45°C. Organic solvents (water miscible only) and small amounts of neutral salts, (KCl, Na 2 SO 4 ) depress the initial rate and the maximum conversion. The addition of small amounts of catalysts like Cu 2⊕ , Mn 2⊕ , Ag oplus; increases the initial rate but no appreciable increase in the limiting conversion is observed.