VISCOELASTIC PROPERTIES OF AMORPHOUS POLYMERS .2. ANOMALOUS TEMPERATURE-DEPENDENCE OF THE STEADY-STATE RECOVERABLE COMPLIANCE IN LOW-MOLECULAR-WEIGHT POLYMERS

Previous study of the viscoelastic behavior of low molecular weight polystyrenes found that the steady-state recoverable compliance, J(e)o, decreased markedly with temperature as the glass temperature, T(g), was approached from above. This anomalous viscoelastic property of polystyrene was explained by a model of coupled molecular motions. Application of the coupling model to low molecular weight poly isobutylene (PIB) leads to the prediction that the anomalous marked decrease of J(e)o will not be observed in PIB. This prediction made for the behavior of polyisobutylene was verified by new creep recovery measurements on a specimen of low molecular weight. The physical reasons for the observation of a breakdown of the Rouse model (modified for undiluted polymers) for low molecular weight polystyrene and the absence of it in polyisobutylene are given. The explanation, based on the coupling model, is illucidated by detailed comparisons between the viscoelastic properties of polystyrene and polyisobutylene.