Isothermal chemical reactions of network forming monomers or functional polymers produces a continuous increase in the systems Tg and the accompanying cooperative segmental relaxation time (a process). Both broad-band dipolar relaxation spectroscopy (DRS) ―? probing the a process via dipolar reorientational mobility, and dynamic light scattering (DLS) ― probing the a process via correlation times of density fluctuations, were used to monitor the system in-situ (to our knowledge, the first study of its kind). An excellent agreement was found between DRS and DLS for the a process characteristic parameters: relaxation time and KWW stretched exponential parameter (characterizing the relaxation breadth). It was concluded that the broadening of the a process is due to a general phenomenon: the microscale heterogeneous nature of glass formers.
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