Vulcanization of crepe rubber by sulfur monochloride. Part II. The dilatometric method

Abstract

AbstractThe kinetics of the reaction between natural rubber hydrocarbon and sulfur monochloride is investigated in dilute hydrocarbon solution by the dilatometric technique. Control experiments with trilaurin and triolein show that the reaction requires unsaturated linkages in the compound to be cold‐vulcanized. The extent and rate of the nonaccelerated reaction with rubber is shown to depend strongly on the nature of the solvent. Moreover, the nonaccelerated reaction is autocatalytic in nature, and exhibits kinetics that are first order with respect to sulfur monochloride. The accelerating effects, on the reaction, of Butyl 8, mercaptobenzothiazole, dibutylammonium dibutyl‐dithiocarbamate (DBA), and methanol are investigated and it is shown that, in the presence of sufficient Butyl 8 or DBA, the autocatalytic nature of the reaction is changed to one that is kinetically of pure first order. The accelerated (Butyl 8) reaction is found to be first order with respect to sulfur monochloride. The accelerated reaction is further shown to be first order with respect to DBA and second order with respect to methanol. A free radical mechanism is proposed for the nonaccelerated reaction, involving attack by the intermediate $ \mathop {\rm S}\limits^ * {\rm \bond S \bond Cl} $ at the double bonds of the rubber molecule. It is suggested that accelerators function by reacting with sulfur monochloride to produce the active intermediate $ \mathop {\rm S}\limits^ * {\rm \bond S \bond Cl} $.