Glass transition of random heteropolymer melts

Random heteropolymers (RHPs) have been widely used as toy models for protein folding, and in many industrial and biological scenarios. Here, we use atomistic MD simulations to explore the factors affecting glass transition temperature (T_g) of a complex class of RHPs. Our random copolymers consist of four monomers with a methacrylate backbone. We explore the dynamical features in polymer melts of random sequence mixtures and show that instead of a sharp glass transition as happen in PMMA, RHPs show a soft transition. However, we show that in both systems there exists an “entropy crisis”, i.e. the backbone configurational entropy becomes extinct. Interestingly, the chain mobility depends on the contents of ionic monomers and types of counterions when they are present. The spatial heterogeneity during the glass transition is also found to be related to both chemical structure and sequence. The comparison with the single-chain shows the effects of breathing dynamic in aqueous systems or vacuum environments. Our work thus indicates that RHP melts are excellent system to investigate the effects of chemistry on T_g. This work is supported by the Defense Threat Reduction Agency contract HDTRA11910011.