DIELECTRIC NORMAL-MODE PROCESS OF POLYISOPRENE IN BLENDS AND IN NETWORKS

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 greater-than-or-equal-to M(e)-degrees (congruent-to 5000, the MW between entanglement for bulk PI), the relaxation time, tau-n, of the probe was proportional to M3, obeying the original tube model. However, the M dependence of tau-n of PI probes trapped in NR or BR networks was puzzling: for those in NR and in high cis-BR, tau-n proportional M3.6, which is similar to bulk narrow-distribution PI; while for those in an-BR, tau-n proportional M3, which is similar to that of the dilute blends of low-M probes in non-cross-linked high-MW matrices.