Study on Relaxation of Entanglement Network Structure with Use of Differential Dynamic Modulus as a Probe

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We have prepared four monodisperse polybutadienes (Mw = 1.4x10^5-7.2x10^5d) by anionic polymerization technique. Vinyl contents of the samples were all 70%. Quantitative interomolecular cross-link can be introduced to the samples by hydrosilation with p-bis(dimethylsilyl)-benzene. In this study, lightly cross-link (Mc/Me-7) was introduced. Under large shearing deformations, anisotropic conformation of the chain occurs in both uncroo-linked and cross-linked samples, but there is no change in entanglement density in the latter sample.We have observed the change in entanglement network structure in both samples under large shearing defotrmations with the use of differential dymnamic modulus as a probe. Differential dynamic modulus can be measured by superposed small oscillatory deformation on a large shearing deformation at a frequency falls down in the middle of the rubbery plateau. Deformations were given in a single-step and double-step fashions. The results were discussed with Doi-Edwards Tube Model and BKZ Model. It can be concluded that there is clear correspondence between nonlinear viscoelastic properties of polymer dense systems and change in entanglement network structure, and change in entanglement network structure under large deformations are due to two factors of chain anisotropy and decrease in entanglement density.