Langevin dynamics simulation of crystallization of ring polymers.

We have studied the crystallization of ring polymers using Langevin dynamics simulations with a coarse-grained united atom model. We show that there are marked differences in the crystallization of single ring polymers in comparison to single linear polymers. Contrary to expectations from equilibrium thermodynamics, ring polymers melt at lower temperatures than linear polymers. An analysis of the early stage crystallization mechanism shows that ring and linear polymers crystallize through the birth of baby nuclei with their coarsening depending uniquely on their topology. The single ring polymers nucleate faster than the single linear analogs and into several metastable lamellar thicknesses, although the motion of the monomers in both cases is comparable. Additionally, using multiple polymer molecules, we find that the secondary nucleation of ring polymers proceeds with free energy barriers, as opposed to linear polymers where no barriers are found. Our results are in qualitative agreement with some experiments, while in disagreement with some other experiments, indicating additional roles by chemistries of ring and linear polymers. Our simulations are designed to explore only the topological effects without any consideration of non-universal chemical effects for our particular model.