Permanganate–oxalic acid as a redox initiator of acrylonitrile polymerization in aqueous media. Part III. Kinetics and DP

Abstract

The kinetics of the aqueous polymerization of acrylonitrile initiated by the permanganate–oxalic acid redox pair have been studied gravimetrically at 32±0.2°C. The rate of polymerization is independent of oxalic acid concentration over a small range. The catalyst exponent varies continuously with the catalyst concentration, being 0.9 at low catalyst concentration and 0.27 at high catalyst concentration at a monomer concentration of 0.30M. The monomer exponent is nearly unity in the concentration range 0.30M and above. The molecular weight of the polymer is independent of oxalic acid concentration in the range where the rate of polymerization is independent of the oxalic acid concentration but decreases at higher concentration of oxalic acid with increasing concentration of catalyst and temperature. The overall activation energy was found to be 8.6 kcal./mole. Addition of salts such as Na₂SO₄ depresses the rate of polymerization, but the addition of MnSO₄ at low concentrations increases the rate, whereas at higher concentration the initial rate falls. It has been suggested that hydrated Mn³⁺ ions cause oxidative chain termination of polyacrylonitrile radicals. Complexing agents, such as fluoride ions, ethylene-diaminetetraacetic acid, etc., decrease the rate of polymerization, whereas addition of detergents enhances it.