Chain scissions in a polymer network

Abstract Relations between the soluble fraction and the number of effective chains between crosslinks in a three‐dimensional network undergoing a scission reaction have been derived. Three limiting cases have been considered: (a) random scission in the chains, (b) scission in the chains directed by the crosslinks, and (c) scission of the crosslinks. The number of scissions can be computed from the fraction of soluble material in a degraded network, as determined experimentally. This procedure has been applied to the oxidation of a natural rubber vulcanizate. In a natural rubber sulfur‐Santocure vulcanizate, the scission reaction accompanying the oxygen absorption at 100°C. does not involve opening of the crosslinks, but it remains undecided whether the scission in the chains is directed or at random. At each chain scission about 5–10 molecules of oxygen are taken up by the rubber at 100°C. under various conditions, this number being apparently independent of the rate of oxidation, the absence or presence of antioxidants and metal stearates as catalysts, and the oxygen pressure.