Abstract
The various types of segmental motions occurring inside a polymer chain are presented and discussed as well as the most suitable expression for the orientational autocorrelation function (OACF) involved in spectroscopic techniques such as fluorescence anisotropy decay (FAD) and 13C NMR relaxation. FAD studies on anthracene labeled polybutadiene and 13C NMR on various low T g polymers show that the segmental dynamics of polymers can be described by considering: (1) conformational jumps leading to bond orientation diffusion along the chain sequence, and (2) additional librations at much higher frequencies, with an amplitude strongly dependent on the considered atomic group in a given chemical structure. The T-dependence of the correlation times associated to the conformational jumps proves that the segmental motions observed by these techniques are involved in the glass-rubber transition phenomenon. Further, the comparison of the results obtained on various polymers show that the polymers have similar segmental dynamics when they are at temperatures where their friction coefficients, determined from melt viscosity, are identical.
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