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An equation, based on thermodynamic considerations to relate the glass transition temperature, Tg, to compositional variation of a polymer system, is adapted in this article for modeling the Tg vs. fractional conversion (x) relationship of reactive thermosetting systems. Agreement between the adapted equation and experimental Tg vs. x data is found for several thermosetting crosslinking systems (i.e., epoxies and cyanate ester/polycyanurate) as well as for reactive thermosetting linear polymer systems (i.e., polyamic acid and esters to polyimides). The equation models the experimentally obtained Tg vs. x behavior of thermosetting systems which include competing reactions. Agreement for widely varying molecular structures demonstrates the generality of the equation. The entire Tg vs. x relationship can be predicted for a thermosetting material by using the Tg vs. x equation and the values of the initial glass transition temperature, Tg0, the fully reacted system glass transition temperature, Tg∞, and the ratio of the change in specific heat from the liquid or rubbery state to the glassy state (Δcp) at Tg0 and Tg∞, Δcp∞/Δcp0. The values of Tg0, Tg∞, and Δcp∞/Δcp0 can be measured generally from two differential scanning calorimetric experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 3–14, 1997
Venditti et al. (Fri,) studied this question.