Vulcanization of Crepe Rubber by Sulfur Monochloride. II. The Dilatometric Method

Abstract

Abstract The vulcanization of rubber by sulfur monochloride is believed to consist of the cross-linking of adjacent isoprene units by thio-ether bonds. Such a reaction, involving polymer aggregation, should be accompanied by an increase of the density of the rubber, and, by choosing a suitably delicate technique, it should be possible to measure the rate of vulcanization by observing density changes. A dilatometric method seemed most suitable, and it was found that the reaction could indeed be followed by observing the rate of decrease of volume of the system rubber-sulfur monochloride when dissolved in a suitable solvent. Initial experiments showed that, during cold vulcanization, the system underwent a volume contraction which was of the order of 10 per cent with respect to the rubber. This comparatively large contraction allowed one to work with extremely dilute solutions (<0.3% w/w) of rubber. It thereby became possible to study the systems under more ideal kinetic conditions of high dilution than has been hitherto possible. In the present investigation, it has not been possible to do more than establish the broad outlines of the kinetic behavior of the system, and, on this basis, to propose feasible mechanisms for the cold vulcanization process.