Temperature dependence of the configurational entropy of undercooled melts and the nature of glass transition

The configurational entropy as well as other related thermodynamic properties of a (poly)disperse glass-forming polymer melt have been calculated exactly in terms of a lattice-hole model and within the framework of the mean field approximation (MFA). One of the main results of the calculation, in which the average “stiffness” and the mean degree of polymerization (association) of the melt appear as temperature-dependent entities, is that for the first time a single analytical expression for the configurational entropy has been established which predicts a noncatastrophic behavior of the undercooled liquid. For certain, “realistic,” values of the energy parameters obtained, the results are consistent with previous theoretical and experimental investigations, although the entropy curve in the region of the supposed second-order phase transition (Gibbs and Di Marzio 1]) is considerably leveled off, and no abrupt changes of its derivatives are to be expected. Qualitative agreement with existing data is good, and ways for further refinement of the model are also discussed.