SECONDARY AND SEGMENTAL RELAXATION IN POLYBUTADIENES OF VARYING MICROSTRUCTURE - DIELECTRIC-RELAXATION RESULTS

The dielectric behavior of polybutadiene copolymers with different com positions of 1,2 and 1,4 units is analyzed to study the influence of t he microstructure on the relaxation spectrum, especially the beta rela xation. The experimental data were obtained between 10(-2) and 10(6) H z and temperatures above and below T-g. Above Tg, the relaxation spect ra are described by the superposition of two processes, the main a rel axation at low frequencies and a beta relaxation at high frequencies. The a relaxation has the typical Vogel-Fulcher-Tammann behavior and ex hibits a quasi-linear shift of time scale upon change of the vinyl con tent. The high-frequency process shows Arrhenius behavior only in the case of the homopolymers. For the other samples with a mixture of micr ostructures, spectral broadening occurs and deviation from the Arrheni us behavior is observed. In these samples, the relaxation can be model ed by the simple assumption that the high-frequency process consists o f a superposition of two separate processes, each with the properties of the beta relaxation of one of the homopolymers. This suggests that secondary relaxations can relax quite independently from the segmental relaxation and are therefore restricted to a very local environment i nfluenced by intramolecular interaction.