Stress-Temperature Studies of Transitions in Rubbers

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Abstract
The stress-temperature method was employed as a means of studying the apparent ``second-order'' transition occurring in rubbers. The rubbers studied were a natural rubber gum, a butyl gum, a loaded GR-S, and a loaded Hycar OS-10. Pronounced stress relaxation was observed for all rubbers at temperatures not too far below the transition region, but not at temperatures a few degrees above the transition. For both the butyl and the Hycar OS-10 rubbers the transition temperature was observed to depend strongly upon extension, the transition temperature decreasing with increasing sample extension. No such dependence upon extension was observed for the natural rubber stock. Comparison data were also obtained from volume dilatometric studies. With the exception of the data for natural rubber, the transition temperatures determined by the volume dilatometric method were somewhat lower than the lowest values obtained in the stress-temperature studies.