Chain Scissions in a Polymer Network

Abstract Relations between degree of crosslinking and gel fraction in a polymer have been derived by several authors. An important parameter in these relations is the crosslinking index γ, the average number of crosslinks to which one original polymer molecule is linked. The relations have been applied to the determination of the degree of crosslinking in linear polymers, but they can be used as well to calculate the soluble fraction of the network in a crosslinked polymer that has been subjected to a degradation process. It will be shown in this paper that a simple relation exists between the soluble fraction of a network that has undergone scission and the effective number of chains in the gel fraction (as determined by swelling measurements). The fraction of soluble material in the degraded network is a measure of the number of scissions. This problem bears upon natural-rubber vulcanizates, which give increasing amounts of extractable material and increasing degrees of swelling on the absorption of oxygen.