Different Routes To The Glass Transition: A Comparison Between Chemical And Physical Vitrification

Despite the differences in the molecular processes involved in chemical and physical vitrification, surprising similarities are observed in the dynamics and in the thermodynamical properties of the resulting glasses. We report on a systematic study of reactive glass-formers undergoing a process of progressive polymerization of the constituent molecules via the formation of irreversible chemical bonds. The formation of most of the materials used in engineering plastics and the hardening of natural and synthetic resins, including epoxy resins, are based on chemical vitrification. The clear analogies characterizing the dynamic evolution of physical and chemical glass-formers, on the time scale of the structural and the low-frequency vibrational dynamics, are briefly reviewed.