Discussion of Two Models for the Glass Transition Temperature

In Bovey/Winslow (1979) [1] pp. 366-367, there are presented d Tg / d P according to Goldstein (1963) [2]: d Tg / d P = (βl - βg) / (αl - αg) or O'Reilly (1962) [3]: d Tg / d P = TV (αl - αg) / ΔCp. O'Reilly presented a TABLE showing how the second equation agrees with the experiment and that will be included here. Goldstein maintains that the two expressions are equal, but Fanggao, et al (1996) [4] say that O'Reilly is correct while Goldstein gives values that are "appreciably higher" than d Tg / d P at the glass transition. This paper will examine Goldstein's derivation to ascertain why BOVEY/WINSLOW says (βl - βg) is a questionable quantity.