TG–Temperature property (TgTP) diagram for thermosetting systems: Anomalous behavior of physical properties vs. extent of cure

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Abstract
The relationships between the isothermal physical properties in the glassy state of amorphous thermosetting crosslinked polymers and chemical conversion are anomalous and complex. In this manuscript, a generalized framework for correlating the basic physical properties of a high‐Tg thermosetting amine/epoxy system vs. extent of cure at isothermal temperatures from above Tg to deep in the glassy state is reported in terms of the Tg‐Temperature Property (TgTP) Diagram. The framework arises from consideration of the isothermal shear modulus and the isothermal physical aging rate vs. extent of cure, both of which display maxima and minima throughout a wide range of temperatures below Tg. Use of Tg as a direct measure of conversion results in linearization of the relationships between the temperatures of the maxima and minima of the physical properties and extent of cure in the TgTP Diagram. The anomalous behavior is related to specific phenomena, such as the glass transition (vitrification) and the glassy‐state β‐transition (Tβ), the temperatures of which change with conversion, and also to gelation. The different types of behavior of a property of the material vs. extent of cure correspond to different regions in the diagram. Such simple diagrams are intellectually useful for understanding the properties of materials for both undercured materials (with change of conversion) and fully cured materials (with change of stoichiometric ratio). © 1993 John Wiley & Sons, Inc.

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