DIELECTRIC STUDY OF SUBCHAIN DYNAMICS AND DIMENSION - BUTADIENE-ISOPRENE BLOCK-COPOLYMERS

Dielectric normal mode relaxation was studied for dilute and semidilut e hexane solutions of butadiene (B)-isoprene (I) block copolymers in w hich the polyisoprene block has the component of dipole moment aligned parallel to the chain contour (Type-A dipole moment) while the polybu tadiene block does not. Thus, the fluctuation of the end-to-end vector of a portion of a chain labeled by type-A dipoles was observed. The r esults indicate that BI diblock copolymers exhibit a single loss peak while BIB triblock copolymers exhibit double peaks. This behavior can be qualitatively explained by the Rouse-Zimm theory. In dilute solutio ns, the loss maximum frequency and the shape of the loss curve agree w ell with the Zimm theory. In semidilute solutions, the loss curve broa dens more than the theoretical loss curve calculated by either the Rou se theory or the Doi-Edwards theory. The broadening of the loss curve can be explained by the coupling theory proposed by Ngai and his co-wo rkers. The mean square end-to-end distance, [r(2)], of the PI block wa s estimated from the relaxation strength, Delta epsilon. The expansion factor, alpha, for [r(2)] agreed approximately with that of home PI s olution in heptane.