Modeling of Methyl Group Rotations in PMMA

Abstract

This paper explores a simple quasi-static approach to the study of conformational changes in polymers in condensed phases. Essentially, a conformational change is driven in steps by a forcing potential and the change in energy of the system is monitored as the transition path is followed. The technique is of interest since it has the potential of yielding the distribution of activation energies for processes which occur on time scales too long for study by molecular dynamic (MD) techniques. In order to test its validity, however, we have applied it to the study of the rotation of the ester methyl group in poly(methyl methacrylate) (PMMA) and compared its predictions with those of direct molecular dynamics simulations and experimental quasi-elastic neutron scattering data. Since the experimental data were analyzed in terms of a Kohlrausch−Williams−Watts (KWW) correlation function, the simulation data are analyzed in terms of fitted KWW τ and β values. We find that the quasi-static approach yields values of...