Study On Dual Dynamic Mechanoresponsive Polyurethane Networks Based On Hydrogen Bond And Dynamic Covalent Bond

The dynamic covalent polymer network combines the advantages of both thermoplastic polymers and thermosetting polymers,and has attracted much attention in the scientific community.The reversible process of the breaking and reconstruction of dynamic covalent bonds overcomes the difficulty of recycling traditional thermosetting polymers,alleviates environmental problems such as plastic pollution and waste,and expands the application scope of the polymer field.Dynamic covalent bonds guide the topological rearrangement of polymer chain segments,which not only endow polymers with self-healing,stimulus response,recyclable and reusable property,but also play important roles in drug delivery and release,medical diagnosis,flexible devices,and 3D/4D printing.However,due to the weak bond energy of dynamic covalent bonds,most of the dynamic covalent polymer networks have poor mechanical properties now,which limits the application of these polymers in actual production and life.In addition,it is also urgent to explore the similarity,specificity and mechanism of action between dynamic covalent bonds and other secondary interaction systems(such as H-bonding)in polymer materials.Focusing on the current problems in dynamic covalent polymer networks,we designed a dual dynamic polymer network(DDPNs)based on the dynamic covalent compound unit(BPID)and the hydrogen bond unit(U2-diol).Compound BPID has four hydroxyls,which is a dynamic covalent compound based the reversible exchange reaction of carbon-carbon free radicals.After BPID is connected to the polymer,a dynamic covalent cross-linking network will be constructed.The compound U2-dioI contains both UPy and urea group,and is connected to the polyurethane side chain to form primary,double and quadruple multi-level hydrogen bonding in the polyurethane,which acts as the physical crosslinking point,thus constructing the second dynamic non-covalent crosslinking network.In this paper,DSC、SAXS and WXRD prove that the UPy sequence modular structure is formed in the polymer.DMA and TGA show that the polymer has good thermal stability.The uniaxial tensile test shows that the polymer has excellent mechanical properties and mechanochromic responsiveness.Then,through RGB,VTSAXS analysis,the mechanism of the dynamic unit bond breaking in the system is speculated.The analysis shows that the breaking of the polymer hydrogen bond is prior to the dynamic covalent bond.Finally,the experiments show that the polymer has good self-healing and recoverable properties.