Topological Catenation Enhances Elastic Modulus of Single Linear Polycatenane

Abstract

Entropic elasticity of single chains underlies many fundamental aspects of mechanical properties of polymers, such as high elasticity of polymer networks and viscoelasticity of polymer liquids. On the other hand, single chain elasticity is further rooted in chain connectivity. Recently, mechanically interlocked polymers, including polycatenanes and polyrotaxanes, which are formed by connecting their building blocks (cyclic and linear chains) through topological bonds (e.g., entanglements), emerge as a conceptually new kind of polymers. In this work, we employ computer simulations to study linear elasticity of single linear polycatenane (or [n]catenane), in which n rings are interlocked through catenation into a chain of linear architecture. Aim of this work is to illuminate the specific role of catenation topology in the elastic moduli of linear polycatenanes by comparing with those of their [n]bonded-ring counterparts, which are formed by connecting the same number of rings but via covalent bonds. Simulation results lead to a conclusion that topological catenation makes [n]catenanes exhibit larger elastic moduli than their linear and [n]bonded-ring counterparts, i.e., larger elastic moduli in the case of [n]catenanes. Furthermore, it is revealed that those [n]catenanes composed of a smaller number of rings (smaller n) possesses larger elastic moduli than others of the same total chain lengths. Molecular mechanisms of these findings are discussed based on conformational entropy due to topological constraints.