Broadband dielectric study of oligomer of poly(vinyl acetate): A detailed comparison of dynamics with its polymer analog

We have studied the dynamics of a trimer of vinyl acetate (3VAc) using broadband dielectric spectroscopy over a wide temperature range to cover its primary and secondary relaxations. The dielectric spectra for the primary process over the entire temperature range have been described in terms of the Kohlraush-Williams-Watts approach [Williams and Watts, Trans. Faraday Soc. 66, 80 (1970)]. The dielectric relaxation is found to show a characteristic crossover in the dynamics at 261 K through the temperature dependence of different dielectric parameters, viz., the relaxation time, shape parameter, and dielectric strength. Unlike in the polymer counterpart, this crossover temperature has been found to be different from the apparent merging temperature of the primary and secondary processes. Moreover, a direct comparison between the shape parameters in the case of 3VAc and poly(vinyl acetate) (PVAc) reflected a near absence of chain connectivity effects on the relaxation shape at the high-temperature side, which is interpreted as the decoupling of side group (containing the dipolar entity) motions from the main chain in the case of PVAc. A secondary relaxation for 3VAc was observed below its glass transition temperature, which is found to show the same activation energy as the beta process in PVAc, for which new measurements have been made. However, their shapes showed different temperature dependences, which are discussed in terms of the molecular structure.