The effects of covalent bonds on the localized relaxations in the glassy states of linear chain and network macromolecules

Dipolar relaxations in the glassy states of five molecular liquids and of their partially and completely polymerized structures, both linear chain and network types, were studied by dielectric measurements for a fixed ac frequency of 1 kHz. Calorimetric measurements were made to determine the number of covalent bonds formed at different instants of polymerization, and the results were combined with the dielectric data to investigate how the height of the relaxation peak indicating localized dipole diffusion changed as the number of covalent bonds in the spontaneously polymerizing material increased. The height, or strength, of the peak due to the localized relaxation process in the molecular liquid gradually decreased and the process approached extinction as the number of covalent bonds approached its limiting value. Concurrently, a new localized glassy state relaxation process evolved at a temperature with a peak 70-90 K above that of the one observed for the molecular state and its height increased and approached a constant value as the number of covalent bonds formed approached its limiting value. These changes were quantitatively similar for the five materials, irrespective of the structure of the macromolecular product. The extinction of the sub-T-g relaxation peak observed originally for the unreacted state has features in common with structural relaxation effects. (C) 1996 American Institute of Physics.