Ting Ge – University of South Carolina
Title: Mechanics of Non-Concatenated Ring Polymers – Effects of Topology Revealed by Molecular Simulations

Abstract: Few aspects are as prevalent and important as topology in polymer mechanics, which provides an essential foundation for versatile functions of polymeric materials. Recent advances in chemistry have enabled the precise synthesis of non-concatenated ring polymers with distinctive topology. While many aspects of the statics and dynamics of ring polymers have been elucidated in the past several decades, the structure-property relationship has not been completely established for ring polymer mechanics. Using molecular simulations with perfect control of polymer topology, we make elastomers and thermoplastics out of non-concatenated ring polymers and investigate their mechanical properties during large deformation and failure. The simulations reveal that the elastomers made of cross-linked ring polymers are significantly more stretchable than cross-linked linear polymers [1]. Compared to linear polymers, the entanglements between ring polymers do not act as effective cross-links. As a result, the stretchability of cross-linked ring polymers is determined by the maximum extension of polymer strands between cross-links rather than between trapped entanglements as in cross-linked linear polymers. The simulations also reveal that the thermoplastics made of ring polymers fail through crazing as their linear counterparts under tensile loading [2]. The stable craze formation indicates the existence of an entanglement network in glassy ring polymers. Nevertheless, the entanglement network consists of only a fraction of the topological constraints that determine the conformations of ring polymers. Both the structural features of the ring polymer craze and the drawing stress during the craze formation are related to the underlying entanglement network. Besides the simulations, molecular theories have been developed to delineate the mechanical behaviors of ring elastomers and ring thermoplastics. The studies demonstrate the use of ring polymers as a transformative pathway to tailor polymer mechanics, propelling a new paradigm of topological polymer physics entering materials science.

[1] “Superstretchable elastomer from cross-linked ring polymers”, J. Wang, T. C. O’Connor, G. S. Grest, and T. Ge, Physical Review Letters 128, 237801 (2022).
[2] “Crazing reveals an entanglement network in glassy ring polymers”, J. Wang and T. Ge, Macromolecules 54, 7500 (2021).