Simulation study of the glass transition temperature in poly(methyl methacrylate)

The glass transition in syndiotactic poly (methyl methacrylate) has been studied through atomistic molecular dynamics simulations performed at temperatures in the range from 297 K to 684 K. The mean squared deviations of atoms, monomers. and molecules from their initial positions were analyzed by means of a technique that separates the effects of diffusive motion from the underlying vibrational motion. The diffusive motion shows a novel power-law variation with time, with an exponent that varies continuously from 0.5 below the glass transition temperature T-g to I at high temperatures. The self part of the van Hove correlation functions for both hydrogen atoms and monomers shows structural arrest at the lowest temperature studied. A second peak in the atomic van Hove correlation is attributed to rotation of the CH3 group.