Dielectric investigations on secondary relaxation of polyarylates: comparison of low molecular models and polymeric compounds

Abstract

This paper focuses on the secondary relaxation (γ-relaxation) behaviour of a set of polyarylates and of the corresponding model systems composed of a single repeat unit and end-groups. The common feature of the compounds is that they contain short dipolar groups (O, CO, COO, SO 2) between successive phenyl units. The method of analysis was dielectric spectroscopy. The aim of the investigations was to characterize the motions connected with this relaxation and their dependence on the chemical structure. It was found that all systems display γ-relaxations which have many features in common, such as for instance the activation energy. Yet differences also exist, for instance in terms of the relaxation strength and the relaxation time distribution, which reveal the impact of the actual chemical structure on the relaxation behaviour. The general conclusion is that the γ-relaxation has to be connected both with inter- and intramolecular motions, the correlation length of which cannot be much larger than the scale set by a single repeat unit.