Chain Ends and the Mullins Effect in Rubber

Abstract It has been suggested that “Mullins softening”, which is the anomalously low stress found in crosslinked rubbers that have been subjected to a reversing deformation history, might be caused by retraction of the chain ends along their primitive paths. Using natural rubber networks made from precursors of varying molecular weight, and an end-linked polytetrahydrofuran rubber, the fraction of chain ends was varied. From stress-strain relationships measured on these rubbers, it is concluded that Mullins softening is unrelated to the presence of chain ends, or to polydispersity in the lengths of network strands.