Dielectric normal-mode process of polyisoprene in blends and in networks

Abstract

The dielectric normal-mode relaxation was studied on dilute blends containing a small amount of cis-polyisoprenes (PI) as a probe in a variety of matrices such as high molecular weight (MW) cis-PI and alkyllithium-polymerized polybutadiene (an-PB), and networks of natural rubber (NR), cis-PB ( cis-BR) and an -PB (an- BR). In the dilute blends of non-cross-linked high-MW PI or PB and low-MW probes with M ≧ M e 0 (⋍ 5000 , the MW between entanglemen for bulk PI), the relaxation time τ n, of the probe was proportional to M 3, obeying the original tube model. However, the M dependence of τ n of PI probes trapped in NR or BR networks was puzzling: for those in NR and in high cis-BR, τ n ∝ M 3.6, which is similar to bulk narrow-distribution PI; while for those in an-BR, τ n ∝ M 3, which is similar to that of the dilute blends of low- M probes in non-cross-linked high-MW matrices.