Topological Catenation Enhances Elastic Modulus of Single Linear Polycatenane

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.

Mechanochemistry of an Interlocked Poly[2]catenane:From Single Molecule to Bulk Gel

Mechanically interlocked molecules(MIMs)are prototypical molecular machines with parts that enable controlled,large-amplitude movement with one component positioned relative to another.Incorporating MIMs into polymeric matrices is promising for the designing of functional materials with unprecedented properties.However,the central issue is the challenges involved with establishing the mechanistic linkage between the single-molecule and the bulk material.Herein,we explore the mechanochemical properties and energetic details of a linear poly[2]catenane with strong intercomponent hydrogen bonding(IHB)revealed by single-molecule force spectroscopy.Our results showed that the individual linear poly[2]catenane chain exhibited typical sawtooth pattern,corresponding to the reversible unlocking and relocking transitions under external force or upon stimulations to dissociate or re-form the strong IHB.Furthermore,when a poly[2]catenane-based polymer gel was prepared using a thiol-ene click reaction between thiol-ended poly[2]catenane and a low-molecule-weight cross-linker,the resultant gel showed excellent mechanical adaptability and dynamic properties,which correlated well with the molecular-level observations.The unique poly[2]catenane structure also contributed to the gel formation with an extraordinary IHB-mediated swelling behavior and shape memory property.Thus our present results demonstrate the functioning of bulk material in a linear tandem manner from the behavior of a single molecule,a finding which should be applicable to other systems with versatile properties and promising applications.