Microcanonical molecular dynamics simulation of the vitreous phase transition of poly(binaphthylphosphazene)

Properties of poly(binaphthoxyphosphazene)s were investigated employing molecular dynamics simulations in the original microcanonical ensemble. In particular we have applied our methodology to the case of isotactic poly-(2,2´-dioxy-1,1´-binaphthylphosphazene) (P-DBNP) in order to estimate the vitreous transition temperature Tg, the energy barrier Δμβ for β-relaxation of the BNP unit, and the thermodynamic entropy of the system. According to our results, the transition is consistent with the Adam-Gibbs model and the specific rotation of α and β-relaxations, which varies significantly with the molecular weight Mw. Our results suggest a rapid interconversion between the different proportions of the chiral R and S repeating units (70% and 30%, respectively) of the non-isotactic copolymer below 523 K and a slow atropisomerization of the DBNP units above 523 K which, in agreement with recent predictions on glassy polymer matrices, becomes much faster as the temperature approaches Tg ~ 573 K.