Dielectric normal mode process of star-shaped polyisoprenes

Abstract

The dielectric behavior of six-arm star-shaped cis-polyisoprenes (6S-PI) with the arm molecular weight Mp ranging from 3.5×103 to 21×103 was compared with that of corresponding linear cis-polyisoprenes (L-PI) which were precursors for the arms. In the entangled regime, the normal mode relaxation time τn of 6S-PI was longer and its dependence on molecular weight was stronger for 6S-PIs than for L-PIs. However, an exponential increase of τn with Mp which is characteristic of a highly entangled star chains was not clearly observed for the 6S-PIs examined, because Mp was not large enough. In the non-entangled regime, the relaxation time τnζ at an iso-friction state of 6S-PI was close to that of corresponding L-PI, as suggested by the Rouse-Ham theory. However, the relaxation mode distribution for 6S-PI was broader than that of L-PI. A model calculation using Rouse-Ham dynamics suggested that the distribution of arm length could possibly lead to a substantial broadening for the relaxation mode distribution. © 1989, The Society of Polymer Science, Japan. All rights reserved.