An Off-Lattice Sanchez-Lacombe Related Equation of State Extensible to Polymeric Foams*

We have extended an off-lattice model of the Sanchez-Lacombe equation of state for pure polymeric systems by including internal degrees of freedom to polymer chains. The extension allows us to predict glass transition temperatures of pure polymeric systems at different pressures. To find unknown parameters of the model only two experimental values are required, namely, the glass transition temperature of the pure polymer at atmospheric pressure and the change in isobaric heat capacity of the pure polymer across the glass transition. The model is also successful in predicting the behavior of isobaric heat capacities of polymer melts as a function of temperature. The model shows that the Gibbs-DiMarzio criterion for the glass transition is invalid for the Sanchez-Lacombe equation of state. Thus, we proposed a new criterion for glass transition temperature calculations. Predictions of the model are compared with a lattice-based version of the Sanchez-Lacombe equation of state for several pure polymeric systems. The proposed model can be extended to multi-component polymeric systems and thus to retrograde vitrification in polymeric foams.