Kinetics and mechanism of acrylonitrile polymerization by p‐toluene sulfinic acid. I. Experimental

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Abstract
p‐Toluene sulfinic acid (TSA) of a high degree of purity, halide free and low p‐toluene sulfonic acid (TOSA) content, was prepared. A cooled‐capillary dilatometer was constructed for the study of the bulk heterogeneous polymerization up to high conversions. Acids were found to show both cocatalytic and inhibitory activities, depending on their type and concentration. The bulk polymerization of acrylonitrile (AN) by TSA shows the usual autoacceleration, which was found however to be depressed or even eliminated by the addition of TSOA and other acids. An autoacceleration phenomenon was found in the solution polymerization of AN at 60°C. by TSA alone. In this case the addition of small amounts of TSOA eliminated the autoacceleration. On addition of TSOA to samples of constant TSA concentration, in bulk or in solution, the initial rate increases, reaches a maximum, and then decreases. A decrease in rate was also observed in the azo‐initiated bulk polymerization on addition of TSA + TSOA. Increasing the concentration of TSOA or H3PO4 in the bulk polymerization, at constant TSA concentration, leads to a lowering of molecular weight. The order of the polymerization with respect to TSA was found to be between 1.1 and 1.5, depending on the TSOA concentration. The results are explained by an enhancement of the TSA initiation through its interaction with a proton, and the role of a TSA‐proton complex in a retardation mechanism.

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