Epoxy polymers : Glass transition/cure degree correlation

The correlation between the glass transition temperature,T g , and the cure degree, α, of epoxy polymers has been analysed on the basis of an extension of the Vogel-Tamman-Fulcher equation for the viscosity of polymers and glasses. A physical meaning has been given to the coefficients of the series expansion of the functionT g=T g (α). This analysis allows one to verify that the experimental (T g ,α) data support the conclusion that, in the case of thermoset polymers, the ideal glass transition temperature,T o, appearing in the VTF equation, is larger thanT g . This conclusion may be supported by the thermodynamic interpretation ofT 0 as the temperature at which the excess entropy of the systems tends to vanish: in the case of partially cured thermosets;T 0 would represent the minimum temperature at which the system becomes able to enhance its cure degree.