Amorphous Cis-1,4-Polybutadiene P-V-T properties from atomistic simulations

Abstract

Context The experimental values of variation of glass transition temperature (Tg) with the pressure are relatively dispersed due to the diversity of microstructure encountered in Cis-1,4-Polybutadiene (PB) and the diversity of technics used for its measurement. Fortunately, atomistic simulations allow to get valuable information for very well controlled chemistry and structures using very well-defined protocol of acquisition. That’s why, atomistic modelling will be used to evaluate the variation of Tg with the pressure for a well-defined amorphous oligomer of cis-1,4 PB.Method Atomistic dilatometry was performed on model of amorphous cis-1,4 PB with a molecular weight of 5402 g.mol− 1. The analysis was carried out by reporting with respect to the temperature, the specific volume, the coefficient of thermal expansion, the total energy, and the constant volume heat capacity averaged over 7 independent configurations. Tait equation was used to fit the evolution of the specific volume for temperatures between 10 K and 700 K and pressure of 0, 60 and 100 MPa.Results The specific volume evolution with temperature and pressure of the melt is predicted to be within 2% of error with the experimental values extrapolated for a similar molecular weight with a very well reproduced coefficient of thermal expansion. The best predictions of Tgs are obtained using the Tait equation fit with a Tg predicted at 162 K at zero pressure and a linear dependence with pressure given a slope of 0.22 K/MPa. As recently observed for PEO and PS, the different calculated properties show hysteresis between the heating and cooling curves.