Structure Design And Color Change Efficiency Regulation Of Stretch Mechanochromic Polyurethane Elastomer

Spiropyran-based polyurethane elastomer（SP-PUE）is a new and developing functional polymer material.The mechanochromic behavior of functional monomer spiropyran-based polyurethane elastomer（SP-PUE）can directly reflect the degree of material damage.Therefore,it has application potential in the fields of memory storage,information security,ink-free writing,sensors and biomedicine.But there are obvious constraints to the application of such materials:（1）The range of adjustable mechanochromic efficiency of materials is small Different application scenarios require materials with different discoloration efficiency.A single mechanochromic material is difficult to meet the various application requirements.（2）The discoloration behavior of functional monomer SP occurs through structural transformation,so the mechanochromic behavior of SP-PUE is affected by ultraviolet environment,which limits its application.The recovery rate of SP-PUE after discoloration is faster than that of other polymers,but it still cannot be recovered immediately,which affects its recycling in practical applications.（3）The mechanochromic behavior monitoring of mechanochromism materials is also restricted by a variety of factors.The color of the material itself and individual differences in human eye observation will affect the standardized analysis of material mechanochromic behavior,which limits the users of discoloration materials.Therefore,in order to solve the application problem of SP-PUE in the field of tensile discoloration materials,SP₂-PUEs and SP’₂-PUEs were synthesized in this paper,The mechanochromic behaviors of SP₂-PUEs and SP’₂-PUEs were evaluated numerically and accurately by Matlab software.The work of this paper was as follows:（1）SP2 was synthesized by hydroxylation of the raw materials and connected into the PUE chain segment,SP₂-PUEs were synthesized with the molar ratio of 2:1:1 of diisocyanate（HDI/IPDI）:polytetrahydrofuranediol（PTMG-1000）:1,4-butanediol（BDO）.The mechanochromic behavior of SP₂-PUEs were observed by tensile test of universal testing machine.According to the SAXS and XRD results,the mechanochromic efficiency of PUE could be regulated by adjusting the microphase structure.When the hard segment is irregular and the size is small,the stress of PUE is difficult to be transmitted to SP structure for mechanochromic behavior.（2）SP’2 was synthesized from 2hydroxy-5-hydroxymethylbenzaldehyde and cyclized indole,and used as a functional monomer to synthesize SP’₂-PUEs.The results of ultraviolet irradiation and orientated tensile test show that SP’₂-PUEs has single mechanochromic behavior and recovers quickly after discoloration.（3）The SP₂-PUEs and SP’₂-PUEs discoloration images were read and analyzed by Matlab software and RGB color space,which for analysis and comparison.The results show that Matlab is more accurate than naked eye in analyzing the strain points of PUE color changing behavior.