INFLUENCE OF CROSS-LINKING ON THE MOLECULAR RELAXATION OF AN AMORPHOUS COPOLYMER NEAR ITS GLASS-TRANSITION TEMPERATURE

Temperature-dependent dielectric relaxation spectra of cross-linked styrene-butyl acrylate copolymers were measured at frequencies between 10 mHz and 1 MHz. The results were analyzed using the empirical Kohlrausch-Williams-Watts (KWW) and Havriliak-Negami (HN) formalisms. While the KWW and the HN formalisms were equally well able to fit the experimental data for the uncross-linked copolymer, the HN formalism provided superior fits at high levels of cross-linking. The fitting parameters obtained from the HN routine were used to interpret the data in terms of the model proposed by Schonhals and Schlosser that relates the molecular motion of the polymer with the HN parameters. In this model, n = alphabeta is correlated with the local intramolecular dynamics of the polymer and is not influenced by the level of cross-linking. On the other hand, the parameter m = alpha, which is related to the intermolecular correlations of the polymer chain segments, decreases with increasing level of cross-linking.