The Structural Design Of Spiropyrane-containing Polyurethane And Its Relationship With The Mechanochromism

The mechanochromism materials can directly reflect the stress and deformation state of the material and has a good application prospect in the rehabilitation of sports injury and real-time monitoring of material structure.The functional properties of such materials often depend on mechanochromism molecules.It is a common way to improve the mechanical discoloration effect of small molecules by designing the molecular structure.However,the effective conduction of the stress on the substrate to the discoloration small molecules determines whether the material can effectively utilize the characteristics of the discoloration small molecules in the actual filling system,which greatly affects the response characteristics of the composite.Around how to improve the interaction between small molecules and matrix molecular chain,in order to enhance effective force transmission between matrix and mechanochromism molecules,this paper use spiropyran as mechanochromism molecules to adjust interaction between mechanochromism molecules and matrix polyurethane chain and the phase structure of polyurethane by hydroxylation of spiropyran and rare earth modification.The effects of spiropyran polyhydroxylation and rare earth modification on the structure and mechanical response of composite materials were studied in detail,expected to establish a method for controlling the response characteristics of the mechanochromism composites from the mechanical action of mechanochromism molecules and matrix.For this purpse,the main research contents include:1)design spiropyran derivatives with different number of hydroxyl groups,establish the synthesis method of polyhydroxylated spiropyran derivatives,and study the influence of hydroxylation on the discoloration effect of spiropyran;2)prepare spiropyran/polyurethane composites,study the effects of different hydroxyl groups on the structure of polyurethane and on the interaction between small molecules and matrix,establish an evaluation method of discoloration efficiency based on effective conduction,and clarify the relationship between composite structure and discoloration response characteristics;3)introduce rare earth elements into spiryrane/polyurethane composites to study the regulatory effects of rare earth ligands and rare earth complexes on the structure and chromic response of composites,and explore the possibility of enhancing the chromic effect of composites through the introduction of the second functional molecules.Based on the in-depth and detailed research work,the main conclusions are as follows:1)Spiropyran derivatives with different number of hydroxyl groups were synthesized successfully.The existence of hydroxyl groups has no obvious effect on the discoloration response of spiropyran,all derivatives show the properties of the discoloration response under the excitation of ultraviolet light and the structure recovery under the condition of visible light.The polyhydroxyl groups in spiropyran derivatives have equal reactivity with isocyanate.2)Nine different spiropyran/polyurethane composites were prepared by solution prepolymerization.The spiropyran derivatives with different structures have different forms in polyurethane matrix.The two hydroxyl groups of dihydroxy spiropyrans can effectively "grasp"the polyurethane main chain,so that the stress can be transferred to the dihydroxy spiropyrans more effectively,resulting in the structural change and therefore generate a force chromic response.Moreover,the composite materials do not loss of mechanical properties and thermal stability while having the response of force discoloration.3)Establish a quantitative expression relationship between the force conduction behavior and color change efficiency of spiropyran/polyurethane composites,and determine ? value to describe the degree of force change of composites.With the increase in the number of hydroxyl groups in spiropyran derivatives,the force conduction efficiency between spiropyran and polyurethane increases from 5.7×10-6 to 1.4×10-5.4)Under tensile conditions,the tensile stress of spiropyran/polyurethane composites destroys the microphase structure of polyurethane,and the polyurethane chain is oriented along the tensile direction,thus effectively transferring the load to spiropyran.Different hydroxylated spiropyranes affect the microphase structure of polyurethane and then affect the transfer of force.5)Complexes containing rare earths with different ligand structures were synthesized.The process for modification of spiropyran/polyurethane composites by rare earth complexes was established.The possible "antenna effect" between the ligand and the complex can realize the energy transfer between the complex and the spiropyran/polyurethane composite system,and present different color change response,which provides the possibility for further realization of the multiple color change caused by the force of the composite.