Increased rates of initiation of polymerization by 4‐4′‐dicyano‐4‐4′‐azopentanoic acid in the presence of ferric salts

The initiation of the polymerization of acrylamide by 4‐4′‐dicyano‐4‐4′‐azopentanoic acid in aqueous solution has been studied kinetically at 25°C. Ferric chloride and ferric sulfate were used to terminate polymerization so that rates of initiation could be calculated from the rates of production of ferrous iron. Velocity coefficients at 25°C. for the initiation reaction were found to be (25.7 ± 2.8) × 10−7 sec.−1 for the ferric chloride terminated reaction and (73.6 ± 0.6) × 10−7 sec.−1 for the ferric sulfate‐terminated polymerization. The value reported for the initiation reaction when acrylamide is polymerized in the absence of metal salts is 1.29 × 10−7 sec.−1. Velocity coefficients for the termination reaction have been calculated from the overall rates of polymerization obtained with ferric salts present. In the case of the ferric chloride‐terminated reaction, it has been shown that the rate of polymerization is reduced by increasing the total concentration of chloride ions. Termination velocity coefficients at 25°C. for the inner sphere complexes FeCl2+·5H2O and FeSO4+·4H2O have been calculated to be 18.9 × 104 and 7.98 × 104 l./mole‐sec., respectively. The dependence on the concentration of ferric chloride of the molecular weights of the polymers produced has also been considered.