SLOW DIELECTRIC-RELAXATION OF ENTANGLED LINEAR CIS-POLYISOPRENES WITHASYMMETRICALLY INVERTED DIPOLES .1. BULK SYSTEMS

Global motion of entangled linear cis-polyisoprene (PI) chains in mono disperse systems was examined through their slow dielectric relaxation behavior. For this purpose, a series of dipole-inverted PI chains of (almost) the same molecular weight M congruent-to 48 x 10(3) was made via multistep coupling of two living PI anion precursors of various M1 and M2 = M-M1 (less-than-or-equal-to M1) with a bifunctional terminat or, p-xylylene dichloride. Those PI chains had dipoles that were paral lel along the chain contour but inverted once at a contour distance M2 from one chain end, and their slow dielectric relaxation corresponded to fluctuation of a vector DELTAR(t) = R1(t) - R2(t), with R1(t) and R2(t) being the vectors that connect the dipole inversion (DI) point a nd the two chain ends at time t. Because of the differences in the DI point locations M2, the PI chains of (almost) the same M and thus of t he same global motion exhibited remarkably different dielectric loss ( epsilon'') curves: For PI's with M2 = M/2 (DI at the chain center) and M2 = 0 (DI at chain end, i.e., without DI), the dielectric relaxation time was found to be 3.9 times shorter for the former but the relaxat ion mode distribution was the same. For 0 < M2 < M/2, the epsilon'' cu rves were intermediate of these two extremes and exhibited a bimodal r elaxation mode distribution. These features of the dipole-inverted PI' s at low frequencies were reasonably well described by a model conside ring reptation and Rouse-type constraint release (CR) for the cases of M2 = 0 and M/2. However, nonnegligible disagreements were found for t he cases of intermediate M2, indicating a necessity of refining the mo del. Further analyses of the epsilon'' data enabled us to obtain infor mation on low-order eigenfunctions f(p)(n) for a local correlation fun ction C(n,t;M) = (1/a2) [u(n,t).u(m,0)], with u(n,t) being a bond vect or for nth segment at time t and a2 = [U2]. The experimental f(p)(n) ( p = 1-3) were not largely but certainly different from the model eigen functions and exhibited nonsinusoidal n dependence. This n dependence appeared to be related to an extra relaxation mechanism (other than re ptation and Rouse-type CR) that had a significant effect at chain ends .