Atomistic Molecular Insight into the Time Dependence of Polymer Glass Transition.

The most atomistic molecular details of polymer glass transition were analyzed through the frozen torsions in our molecular dynamics simulations. Different observation times were used to determine the frozen fractions and frozen chain lengths. The glass transition temperature was found to coincide well with the temperature at which the frozen fractions were reduced to 1/e. The frozen chain segments grow as the temperature decreases in a similar way with that of linear polymerization, and the inverse number-average frozen chain length leads to the formulation of configuration entropy during glass transition. The ideal glass transition temperature extrapolated to zero configuration entropy corresponds well with those reported in the literature, and the relation between the relaxation time and the configuration entropy shows perfect agreement with the Adam-Gibbs theory around the glass transition temperature. Volume spanning clusters are formed at the low temperature end, which might serve as a premature prototype for the formation of the "ideal glassy state" with limited accessible configurations.