The glass transition in polymer melts - results from neutron scattering

The polymer dynamics near the glass transition can be classified into three different categories: (i) anomalous low-frequency vibrations, the so-called boson peak, which are accompanied by a fast relaxational process; (ii) secondary and higher-order relaxations, which are assumed to involve only local molecular motions and (iii) the structural relaxation underlying the flow processes which freezes at the glass transition. This paper presents inelastic and quasielastic neutron scattering data on these dynamical processes, emphasizing polybutadiene. In the light of these data, current models on the dynamic glass transition are inspected. In a second step, recent experiments on the coherent dynamic structure factor are exploited in order to learn about the molecular nature of the various polymer motions.