Theoretical prediction of the specific heat of polymer glasses

Abstract

Lattice vibrations are incorporated into the Gibbs-DiMarzio configurational entropy theory of glasses. A comparison is made with data compiled by O’Reilly. The resulting theory predicts the specific-heat discontinuity at the glass transition to within 20%. No adjustable parameters are involved; only the chemical structure need be known. The specific-heat discontinuity has three parts. The formula in customary notation is Δcp=R (Δε/kTg)2 f (1−f) +RTgΔα (4−TgΔα/0.06) +0.5TgΔαcp(Tg−). The first part is a configurational term arising from shape changes of the molecules (?50% of total). The second part is a configurational term arising from volume expansion (?30% of total). Finally there is a vibrational contribution arising from the change of the force constants (or characteristics frequencies) with temperature (?20% of total).