Shape Memory Polymer Based On Reversible Bonds And Its Applications

Shape memory polymers(SMPs)are a class of smart materials that can remember temporary shapes and recover to permanent shapes responding with external stimuli.SMPs have a wide range of applications in a variety of fields,including aerospace,biomedicine,flexible electronics,and other fields.Due to the limited species and applications of SMP materials,the development of the SMP has been in a state of stagnation for a long time.This paper mainly studies the new properties brought by the introduction of reversible bonds to SMPs and expands the species and applications of SMPs.Reversible bonds are a class of bonds that can be broken and reconstructed in particular states.In this work,temperature sensitive reversible bonds are introduced into SMP systems.Thus,this novel SMP has another reversible bond activation temperature range besides the phase transition temperature of conventional SMPs.Within this reversible bond activation temperature range,the mechanical properties of the material are greatly affected by temperature.By introducing suitable reversible bonds and adjusting the network structure,the novel SMP exhibits the elastic behavior of conventional SMPs below the reversible bond activation temperature and exhibits the plastic behavior in the reversible bond activation temperature range.This study first explored the effects of supramolecular bonds on the properties of SMPs.2-ureido-4[1H]-pyrimidinone(UPy)is capable of forming dimers by supramolecular forces of quadruple hydrogen bonds.Introduction of UPy dimers into SMPs can greatly affect the properties of SMPs.We found that as the amount of UPy introduced increases,the material gradually transformed from an elastic material to a plastic material.By precisely adjusting the amount of UPy added,we found the elastic and plastic transition point which is also indicated by the formula calculation.Elastic materials near this transition point exhibit a variety of special properties,including ultra-low modulus,strain rate dependence,and mechanical damping characteristics.Next,the thermadapt SMP was studied,and a novel thennadapt SMP with the advantages of fluid processing and solid processing was proposed.The thermadapt SMP can change the permanent shape of SMP at a specific temperature,and realize the post-processing of the permanent shape,which greatly expands the fabricated shapes and application ranges of SMP.In this study,we introduced Diels-Alder(DA)reversible covalent bonds into SMPs to construct a novel thennadapt SMP.The common way of processing polymers is liquid state molding,however,such manufacturing process is limited by the molding technology.At the same time,by plasticity the polymer can be reprocessed in a solid state by means of origami,but this process is limited by the initial shape.The thermadapt SMP proposed in this study can be reprocessed in both liquid state and solid state.This SMP material system combining the advantages of the two processing methods will open up new possibilities for the preparation of complex SMP devices.Inheriting the material system of the previous work,we extended the application of SMPs to the field of optics and achieved the goal of using stress to record information.The polymer system is based on an epoxy system that exhibits a temporary birefringence effect,and material with this effect can observe a stress distribution under a polarized light field after introduction of internal stress.In this work,we realized the stress control of SMPs by the spatial plasticity in the solid state and realized the information recorded by the stress in a digital method.Since the stress is invisible,such information recording mode cannot be read under natural light.However,the invisible stress information is converted into a visible color pattern,thus realizing information reading,in the polarized light field.In addition,by constructing the internal stress information of the shape memory polymer,the material can undergo a two-dimensional to three-dimensional transformation,providing a new idea for all-solid-state 3D printing.