Heat capacity measurements and modeling of polystyrene glass transition in a wide range of cooling rates

• Glass transition of polystyrene is studied with differential-scanning calorimetry.
• Heat capacity curves measured in a wide range of cooling rates (5·10− 6–2 K/s)
• Common theoretical methods (TNM, AG) do not fit experiment with usual parameter sets.
• Curve fitting for these methods is applied, and new values of model parameters were obtained.
• Gutzow–Schmelzer model with new expression for relaxation time bears similar results.

Polymers are known to be good glass formers, allowing one to study glass transition effects as well as to verify the applicability of various theoretical models. In this work experimental and theoretical investigations of glass transition of atactic polystyrene (PS) in a broad range of cooling rates (5·10− 6–2 K/s) are presented. The capability of commonly employed theoretical techniques for Cp modeling to describe the obtained data is considered. It is shown that the extended Tool–Narayanaswamy–Moynihan (TNM) model with Vogel–Fulcher–Tammann–Hesse (VFTH) or Adam–Gibbs (AG) expressions for relaxation time with the common single set of parameters do not fit the experimental data well. Moreover, the values of parameters required to produce an adequate fit of the whole set of heating curves are quite different from their estimates obtained from independent additional experiments. An additional expression for relaxation time is proposed within the Gutzow–Schmelzer (GS) approach for describing the kinetics of glass transition leading to results of similar precision. The obtained results reconfirm the general conclusion that the considered models of glass transition require parameter readjusting for different cooling or heating rates in order to adequately describe the experimental data.