DYNAMICS OF DIPOLE-INVERTED CIS-POLYISOPRENE CHAINS IN A MATRIX OF LONG, ENTANGLING CHAINS - 1 - EFFECTS OF CONSTRAINT RELEASE ON THE EIGENMODES OF THE LOCAL CORRELATION-FUNCTION

For a series of cis-polyisoprene (PI) chains having nearly the same mo lecular weight (M congruent to 50000) but differently once-inverted di poles parallel along the chain backbone, dielectric behavior was exami ned in homogeneous blends in an entangling polybutadiene (PB) matrix w ith M = 263 000. In the blends, the PI chains (5 vol %) were entangled only with the matrix chains. The constraint release (CR) mechanism ma de a negligible contribution to the global relaxation of those PI chai ns. The series of PI chains exhibited quite different dielectric losse s epsilon ''. These differences, reflecting the different location of the dipole inversion point in the chain backbone, were utilized to exp erimentally determine the eigenfunctions f(p)(n) and relaxation times tau(p) defined for a local correlation function, C(n,t;m) = (1/a(2))-[ u(n,t).u(m,0)] = (2/N)Sigma(p)f(p)(n) f(p)(m) exp(-t/tau(p)) with u(n, t) being the bond vector for the nth segment at time t. The f(p)(n) an d tau(p)/tau(1) ratio (p = 1-3) evaluated for the PI chains in the hig h-M PB matrix were found to be close to those determined in a low-M en tangling matrix (M = 9240) as well as in the monodisperse bulk state o f the same PI chains. The PI relaxation was dominated by the CR mechan ism in this low-M matrix, while this mechanism made a moderate contrib ution to the PI relaxation in the monodisperse bulk state. Thus the cl ose coincidence of f(p)(n) and the tau(p)/tau(1) ratio (p = 1-3) in th e three environments indicated that the distribution of the slowest th ree eigenmodes was hardly affected by the CR mechanism. In contrast, f or higher eigenmodes, modest CR effects were observed through differen ces in the shape of the epsilon '' curves at intermediate frequencies for respective dipole-inverted PI chains in the three environments.