Dynamic Vitrification and the Activation Energy of Rubbery Polymers

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Abstract
1. The resistance to brittleness of a wide variety of rubbers was studied by the method of periodic deformation. 2. Dynamic glassing, during which transition from the highly elastic into the brittle state is observed, always occurs in the liquid state of aggregation of a polymer, where the activation energy of molecular rearrangement changes with temperature according to an exponential law. 3. In a small temperature interval the change of the activation energy can be approximated by a linear law; consequently, Equations (1) and (4) expressing the dependence of the temperature of transition of the rubber into the brittle state on the frequency of deformations are satisfied approximately. The constants entering into these equations and their relationship to the activation energy are determined. 4. The activation energy of dynamic glassing is directly proportional to the glass temperature of the polymer and is greater than the activation energy of static glassing by approximately 5–10%, consequently the rate of establishment of the equilibrium structure is greater than the rate of stress relaxation or the rate of development of elastomeric deformation. 5. The relatively high activation energy of dynamic in comparison with static glassing is caused, apparently, by the larger size of the segments of the polymer chain during mechanical action compared to the size during free thermal motion.

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