Extent of the glass transition in polymers envisioned by computation of mechanical properties

F Godey and MO Bensaid and A Soldera, POLYMER, 164, 33-38 (2019).

DOI: 10.1016/j.polymer.2019.01.001

The simulated glass transition temperature (T-g) is usually determined by the dilatometry procedure. However, we recently showed that a greater glass transition domain is uncovered where specific volume, coefficient of thermal expansion and heat capacity vary. This domain extends over 150 K, definitively higher than the experimental 3-5 K, raising the question of the identification of T-g. This article thus presents the computation of the bulk modulus and the Gruneisen parameter of two polymers, polyethylene and polystyrene. Fit of the Murnaghan equation when the system is in mechanical equilibrium, and the volume fluctuation method are used. The first method leads to important standard deviation for values higher than T-g. With the latter procedure, the computing values data are found consistent with experimental data for temperatures higher and lower than the glass transition domain. This study confirms the enlargement of the glass transition domain, and the difficulty to associate T-g with a specific change in the molecular behavior.

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