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

• Published in: Journal of non-crystalline solids 2017-03, Vol.460, p.90-97
• Main Authors: Samith, V.D., Ruíz-Fernández, A.R., Bahamondes-Padilla, V.E., Muñoz-Gacitúa, D., Ramos-Moore, E., Davis, S.
• Format: Article
• Language: English
• Subjects: Differential scanning calorimetry; Glass transition temperature; Microcanonical ensemble; Molecular dynamics simulations; Poly(binaphthoxyphosphazene)s; Thermal degradation analysis
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2017.01.023

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 523K and a slow atropisomerization of the DBNP units above 523K which, in agreement with recent predictions on glassy polymer matrices, becomes much faster as the temperature approaches Tg~573K.