Glass transition temperature versus conversion relationships for thermosetting polymers

TLDR

Tg of partially reacted thermosets depends on thermal history and heating rate, so theoretical Tg–conversion relations must incorporate enthalpy relaxation and entropic considerations of a random mixture of reacted network and monomers. The DiBenedetto equation, confirmed by an extended Couchman approach, accurately predicts Tg–conversion behavior and has been successfully applied to various diepoxy‑diamine copolymers.

Abstract

Abstract Owing to enthalpy relaxation, values of the glass transition temperature ( T g ) for partially reacted polymers may depend on the thermal history of samples and the heating rate used for measurements. Use of theoretical relations between T g and the extent of reaction ( x ) of a thermoset must take this fact into account. The original DiBenedetto equation has been reevaluated as a convenient constitutive equation for expressing T g versus x . An extension of Couchman's approach for the expression of the compositional variation of T g enabled us to derive the same functionality as given by the DiBenedetto equation. Thus, the DiBenedetto equation may be regarded as based on entropic considerations applied to a model of the thermosetting polymer consisting of a random mixture of a fully reacted network with the initial monomers in an amount which depends on the particular conversion level. These two equations have been applied with success to different diepoxy‐diamine copolymers.