Further investigation of the dielectric normal mode process in undiluted c i s-polyisoprene with narrow distribution of molecular weight

Abstract

Dielectric relaxations in undiluted cis-polyisoprene (cis-PI) with narrow molecular-weight distribution were investigated. The normal mode process due to fluctuation of the end-to-end distance and the segmental mode process due to the local segmental motions were observed. The average relaxation time τn for the normal mode process was insensitive to the polydispersity Mw/Mn, but the width of the loss curve reflecting the distribution of the relaxation times increased with Mw/Mn. The slope of the double logarithmic plot of τn against Mw changed at the characteristic molecular weight Mc from 2.0 in the range Mw<Mc to 4.0±0.2 in the range Mw>Mc. It was found that although the half-width is nearly independent of Mw, the tail of the loss curve in the high frequency side broadens with increasing Mw. This indicates that by entanglement effects the distribution of the relaxation time for the normal mode process changes slightly. The segmental mode is found to be almost independent of the molecular weight and the polydispersity factor.