Relaxation times poly melts

A frequency dependence of complex dielectric permittivity of polar polymer reveals two sets or two branches of relaxation processes (Adachi and Kotaka 1993), which correspond to the two branches of conformational relaxation, described in Section 4.2.4. The available empirical data on the molecular-weight dependencies are consistent with formulae (4.41) and (4.42). It was revealed for undiluted polyisoprene and poly(d, /-lactic acid) that the terminal (slow) dielectric relaxation time depends strongly on molecular weight of polymers (Adachi and Kotaka 1993 Ren et al. 2003). Two relaxation branches were discovered for i.s-polyisoprene melts in experiments by Imanishi et al. (1988) and Fodor and Hill (1994). The fast relaxation times do not depend on the length of the macromolecule, while the slow relaxation times do. For the latter, Imanishi et al. (1988) have found... 

Thermotropic LCPs have high melt elasticity, but exhibit little extrudate swell. The latter has been attributed to a yield stress and to long relaxation times (60). The relaxation times for LCPs are normally much longer than for conventional polymers. Anomalous behavior such as negative first normal stress differences, shear-thickening behavior and time-dependent effects have also been observed in the. rheology of LCPs (56). Several of these phenomena are discussed for poly(benzylglutamate) solutions in the chapter by Moldenaers et al. 

Carbon-13 spin-lattice relaxation times are measured for poly(octadecyl acrylate) above and below the melting point of the crystalline side chains. The behaviours of lithium ions in a polyether poly(urethane urea) (PEUU) were investigated by C MAS solid-state NMR. ... 

Ito et have studied relaxation in poly(ethylene sebacate) and poly(deca-methylene-l,16-hexadecane dicarboxylate) using the solid echo technique a and relaxations consistent with dielectric data were observed, the jS process being associated with the ester group. In poly(dimethylsiIoxane), Burnett et al. observed two spin-lattice relaxation time minima at <85 and 200 K and a discontinuity in Ti at 230 K. The low temperature minimum was assigned to methyl rotation, the high temperature minimum to a chain stretching and oscillational mode, and the discontinuity to melting. 

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