Mechanical Behavior of a Polymer at Temperatures through the Glass Transition Temperature

Stress-temperature (constant strain) and length-temperature (constant stress) measurements have been made on Paracril-35 (a butadiene-acrylonitrile copolymer) in the temperature range −80°C to 25°C, which includes the glass-like, transition, and rubber-like states for this material (Tg∼−25°C). Time effects are observed in the transition region, but for temperature gradients used (down to about 1°C in 4 hours) the behavior at low temperatures is unique, indicating the existence of a real transition. This behavior is independent of the strain imposed at room temperature. The shift in transition temperature (in the length-temperature work) with extension is found to give quantitative support to the theory that the transition occurs at a certain minimum volume. In the rubber-like region, behavior is represented by the usual equation of state.