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| - Dynamics of Dipole-Inverted cis-Polyisoprene Chains in a Matrix ofLong, Entangling Chains. 2. Effects of Constraint Release on theCoherence of the Subchain Motion
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| - For cis-polyisoprene (PI) chains having dipoles parallel along their backbone, viscoelasticrelaxation reflects orientational anisotropy of subchains (stress-generating units) at respective times whilethe dielectric relaxation reflects orientational correlation of the subchains at two separate times. Thisdifference between viscoelastic and dielectric relaxation processes enables us to examine the short-timecoherence of subchain motion in individual chains through comparison of these processes. Specifically,for the two extreme cases of perfectly coherent or incoherent subchain motion, viscoelastic moduliandare explicitly calculated from the relaxation times τp and eigenfunctions fp defined for a localcorrelation function describing fundamental features of the dielectric relaxation. On the basis of thesebackgrounds, theandwere calculated for a PI chain (M = 48800) dilutely blended in a high-Mentangling polybutadiene (PB) matrix (M = 263000). (The τp and fp data necessary for this calculationwere obtained dielectrically in Part 1 of this series of papers.) Thewas in excellent agreement withthe G* data of the PI chain whilewas significantly different from the data, meaning that thesubchain motion was highly coherent for the PI chain in the high-M PB matrix. In contrast, the subchainmotion of the same PI chain was found to be incoherent in an entangling PB matrix of smaller M (=9240).The constraint release mechanism made a negligible contribution to the global dynamics of the PI chainsin the high-M matrix while it dominated the dynamics in the low-M matrix. These results indicate thatthe constraint release is an important factor that determines the degree of coherence of the subchainmotion.
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