Atomistic modelling study of relaxation processes in polymers: the beta-relaxation in polyvinylchloride

Activation energies related to the beta-relaxation process in polyvinylchloride were calculated from atomistic simulations. Pure Boyer and Schatzky crank-shaft type motion seem idealised situations which rarely contribute to relaxation in amorphous polymers. However, the activation energies accompanying other types of local conformational transitions were found in the appropriate range to account for the beta-relaxation. Moreover, the present results suggest that local conformational transitions may account for both the beta-relaxation as well as the alpha-or glass transition in polyvinylchloride, whereas motions related to the glass transition involve considerable distortion of the environment next to the conformational transition. The results obtained point out possible answers to long-standing questions concerning the details at the molecular level of the glass-transition and the secondary relaxation mechanism in an amorphous polymer. (C) 1997 Elsevier Science Ltd.