Glass-Transition Temperature of Cyclic Polystyrene: A Computational Study

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 T-0 obtained from the decay of the orientational autocorrelation function of the phenyl bond show a clear upturn.

Automated summary

Molecular dynamics simulations of cyclic polystyrene melts reveal conflicting findings regarding the glass transition temperature, with some experiments confirming the predictions of Gibbs and DiMarzio's theory while others showing contradictory results. Volumetric methods suggest a slight increase in glass transition temperature as the chain length decreases, while dynamics-based methods show more pronounced results. Both diffusion data and orientational autocorrelation function analysis indicate a clear increase in glass transition temperature.