Study On The Synthesis And Properties Of Mechanochromic Elastomers Based On Spiropyran

Mechanochromic elastomer materials have a wide application prospect in the fields of flexible display,intelligent medicine,stress-strain sensing and material damage early warning,however,due to the contradiction of the toughness and resilience of elastomer materials to the structure and movement ability of polymer segments,the development of elastomer materials with high toughness,high resilience and high discoloration sensitivity is still a great challenge.In this paper,from the point of view of the molecular structure design of the polymer,the chemical structure and condensed structure of the polymer are regulated,and the reversible force-sensitive color-changing elastomer materials with high toughness,high elasticity and sensitive response are synthesized,and the application range of force-sensitive color-changing elastomers is expanded.Firstly,the functional small molecules of spiropyran glycol(SP₁)and bisspiropyran(SP₂)were synthesized and characterized by Fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance spectroscopy(~1HNMR)and liquid chromatography-mass spectrometry(LC-MS),respectively.The infrared absorption peak,chemical shift and molecular weight of the characteristic structure were characterized by thermogravimetric analysis(TGA).Secondly,spiropyran glycol and bisspiropyran were chemically modified and used as force-sensitive groups to prepare two kinds of functional polyurethane elastomers by solution prepolymerization.The chemical structure was characterized by ~1H NMR and FTIR.The molecular weight and molecular weight distribution of polyurethane elastomers were characterized by gel permeation chromatography(GPC).The thermal properties and crystallinity of polyurethane elastomers were studied by differential scanning calorimetry(DSC),thermogravimetric analyzer(TGA)and X-ray diffractometer(XRD).The mechanical properties,toughness and cyclic tensile properties of polyurethane elastomers were investigated by universal tension tester,and the resilience and force-sensitive discoloration reversibility of polyurethane elastomers were studied.The fracture toughness of the elastomer can reach?700 MJ/m~3,and the residual strain after 10 cycles is only 50%(the preset strain is 200%).The critical discoloration strain()of elastomers is 170%.Finally,in order to further improve the resilience and discoloration sensitivity of force-sensitive discoloration elastomers,a force-sensitive discoloration polyether ester elastomer was synthesized with polybutylene terephthalate as hard segment and polytetrahydrofuran as soft segment.The molecular weight of the soft segment and the ratio of soft to hard segments in the elastomer were adjusted.The chemical structure of the polymer was characterized by ~1H NMR and FTIR.The molecular weight and molecular weight distribution of the elastomer were characterized by gel permeation chromatography(GPC).The thermal properties and crystallinity of the elastomer were studied by differential scanning calorimetry(DSC),thermogravimetric analyzer(TGA)and X-ray diffractometer(XRD).The mechanical properties,toughness and cyclic tensile properties of elastomers were investigated by universal tension tester,and the reversibility of resilience and force-sensitive discoloration were studied.The fracture toughness of the elastomer can reach?300 MJ/m~3,and the residual strain after 10 cycles is only 23%(the preset strain is 200%).The critical strain of discoloration()is 158%and the discoloration and springback properties remain stable in 10 cycles.