RELATIONSHIP BETWEEN SEGMENTAL AND CHAIN DYNAMICS IN POLYMER MELTS ASSTUDIED BY DIELECTRIC-SPECTROSCOPY

Broadband dielectric spectroscopy in the frequency range from 10(-5) H z to 10(6) Hz is employed to study the relation between alpha-relaxati on and normal mode process for oligomeric polyisoprene and polypropyle ne glycol samples of different molecular weight. It is shown that rela xation time of the alpha-relaxation has a much stronger temperature de pendence than that of the normal mode process. This means that applica bility of the Rouse model to the normal mode relaxation breaks down ne ar the glass transition. This result is further discussed in terms of the different temperature dependence of the two relevant length scales , the correlation length for the alpha-relaxation zeta and the end-to- end vector of the polymer chain. A quantitative evaluation gives more evidence that there exists a characteristic length scale for the alpha -relaxation which is in the order of magnitude of 2 to 3 nm at the gla ss transition temperature.