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A review of recent work by the authors on a relaxation (Tgℓℓ) above the glass transition Tg of amorphous polystyrene is presented. On the basis of experimental data from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA), and of an examination of the literature, it is suggested that Tℓℓ represents a molecularly-based transition. Its main features are summarized by the expressions: Tℓℓ ≃ 1.2 Tg and Tℓℓ ≃Tℓℓ(∞)—KℓℓMn −1, where temperatures are in degrees Kelvin and Kℓℓ is a constant. Jt follows that if Tg is an isofree-volume state, then so is Tℓℓ Further, when Mn≃Mw and M for each component
Gillham et al. (1977) studied this question.