Segmental Mobility of Polymers Near Their Glass Temperature

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Abstract
Glass forming polymers exhibit a rapid rise of activation energy for molecular motion as T is lowered through the glass temperature. This phenomena is explained here in two different but largely equivalent ways. The first method assumes that in order for a polymer segment to move (i.e., rotate or jump) an energy greater than a critical energy E must be localized on it and its neighbors. The second approach stipulates that a segment may not move unless more than a certain critical amount of free volume is associated with it and its neighbors. Both approaches lead to good agreement with experimental data available for polystyrene and polyisobutylene. The critical values of E and the free volume for these polymers are found and shown to be reasonable. Conclusions are drawn concerning factors influencing the glass temperature.

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