Preparation And Mechanical Properties Of Elastomers Based On Cyclic Molecules

High-performance elastomers have demonstrated extensive application prospects in fields such as medical devices,wearable electronic skins,smart sensors,and soft robots.Typically,high-performance elastomers can be achieved by modulating the chemical structure and composition of polymers,such as introducing phase separation,supramolecular interactions,double network structures,or nanofillers into polymer networks.In addition,the performance of elastomers is not only dependent on the chemical structure and composition of polymers but also closely related to their topology.Therefore,designing the topology of polymer networks is also an effective strategy for preparing high-performance soft materials.As an important topological polymer structure,cyclic polymers possess unique physical and chemical properties due to their non-chain-end structure,such as lower characteristic viscosity,gyration radius,higher glass transition temperature,and no entanglement effect.Currently,research on cyclic polymers mainly focuses on their synthesis methodology and the dynamics of solutions and melts.However,there is still limited research on constructing high-performance soft elastomers based on cyclic polymers and investigating the relationship between their structure and mechanical properties.Therefore,this thesis aims to use cyclic molecules to construct elastomers with a high extensibility and toughness,and to investigate the tough mechanisms of cyclic topology-enhanced elastomers.The main research content and results of this thesis are as follows:(1)High-stretch elastomeric materials were prepared using cross-linked cyclic polymers.Cyclooctene-4-ene-6-acetoxyhexyl acrylate(CEACA)was used as a monomer,and cyclic and linear polymers with similar molecular weights were successfully synthesized using the ring-expansion metathesis polymerization(REMP)and ring-opening metathesis polymerization(ROMP)methods.Cross-linked cyclic and linear soft elastomers was achieved via thiol-ene click reactions.Compared with elastomers prepared using linear polymers,it was found that the soft elastomers prepared using cyclic polymers exhibited higher stretchability and toughness due to their more compact conformation and lower degree of entanglement.(2)Using cyclic and linear polymers as additives to achieve toughening of elastomers.Using isobornyl methacrylate as a monomer,a series of cyclic and linear polymers with different molecular weight ranges(10~4～10~6 g/mol)were synthesized using the REMP and ROMP methods,and they were blended into a cross-linked poly(butyl acrylate)network to form composite elastomeric materials.The results showed that the tensile strength and fracture toughness of the composite elastomer increased with the molecular weight of the cyclic and linear polymers.Compared with composites using linear polymer blending,composites using cyclic polymer blending exhibited higher tensile strength and fracture toughness.This toughening mechanism may originate from the matrix polymer interpenetrating into the cyclic polymer network structure,forming an effective mechanical interlocking structure,which substantially delays the relaxation of polymer chains.(3)Using cyclic small molecules as dynamic cross-linkers to form high-performance elastomeric materials.A dynamic cross-linker containing a cyclic nitrogen-boron(N-B)structure was developed and copolymerized with acrylate monomers to form elastomeric materials.The results showed that compared with the elastomer prepared using polyethylene glycol diacrylate as a covalent cross-linker,the elastomer prepared using the cyclic N-B structure of the dynamic cross-linker exhibited higher stretchability and toughness.Additionally,the elastomer also demonstrated rapid self-recovery functionality.