Glass-Transition Temperature of Cyclic Polystyrene: A Computational Study

Abstract: Molecular-dynamics simulations are employed to study the glass transition of cyclic polystyrene melts. Gibbs and DiMarzio’s theory predict an increase in glass transition temperature, T_g upon lowering the length of cyclic polymer chains, which is opposite to the well-known trend for linear polymers. Their theory has been confirmed by some experiments; however, others observe a decrease in T_g upon lowering the chain length instead. When volumetric methods are employed to obtain the glass transition temperature in simulated cyclic polystyrene, a slight increase with decreasing cyclic polystyrene chain length is obtained. This increase is more pronounced when glass transition temperatures are obtained from dynamics. Both the glass transition temperature T_g obtained from diffusion data and the ideal glass transition temperature T₀ obtained from the decay of the orientational autocorrelation function of the phenyl bond show a clear upturn.