Mechanochemiluminescent Elastomers

Due to various kinds of synthetic composition and adjustable mechanical performance,polyurethane(PU)elastomers exhibit excellent properties(high elasticity,high toughness,abrasion resistance,chemical corrosion resistance and low temperature flexibility).Accordingly,polyurethanes have been widely utilized in many significant fields,such as national defense system,mining industry,construction,chemical industry,medical treatment and aerospace equipment.However,inevitable damage and failure of polymeric materials,especially at microscopic structure,could lead to shortened service life and poor performance.As a result,it is crucial to study the damage mechanism of polyurethanes in molecular level.Based on polymer mechanochemistry,we herein synthesized a series of mechanochemiluminescent polyurethane elastomers containing the mechanophore 1,2-dioxetane.By choosing different isocyanates as hard segments to change the structure of polyurethanes,as well as physically blending inorganic nanoparticles into polyurethane elastomers,the stress distribution of the polymeric material could be visualized sensitively.The results can be summarized as follow:1.A series of mechanochemiluminescent segmented polyurethanes(PUs)with different phase separation degrees were synthesized under mild polycondensation conditions,using 1,6-diisocyanatohexane(HDI),2,4-tolylene diisocyanate(TDI),p-phenylene diisocyanate(PPDI),isophorone diisocyanate(IPDI)or diphenyl-methane-diisocyanate(MDI)as the hard segment(HS).4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole was physically blended into all polyurethanes as energy acceptor to increase the light intensity during fracture.Systematic studies based on optomechanical measurements and Differential Scanning Calorimetry(DSC),X-ray Diffractometer(XRD),Small Angle X-ray Scattering(SAXS)and Field Emission Scanning Electron Microscopies(FE-SEM)analyses show that the difference in the chemical compositions of the hard segments leads to different microphase separation behaviours in the bulk,and consequently to the unique stress-strain responses and mechanoluminescence behaviors.Benefitting from relative homogeneous structure and low degree of microphase separation of UTDI,the luminescent signal of UTDI is the strongest at the same applied force,which means the force threshold of UTDI is lower.This work presents a detailed picture of how failure occurs in mechanochemiluminescent polymer materials and improves spatial and temporal resolution of the sensitive probe 1,2-dioxetane.2.Based on the previous study,TDI polyurethane with the lowest force threshold and highly sensitive mechanochemiluminesecent property was selected to be physically blended with commercial inorganic nanoparticles Zinc Sulphide(ZnS).A series of multifunctional mechano-response polymeric materials with gradient content of ZnS were obtained by thermal compress.The mechanical properties of the multi-responsive materials were analyzed by rheological measurements with a high-speed camera recording the in-situ mechanochemiluminescence process.The polyurethanes/ZnS composites stimulated by weak force emit chemiluminescence indicating the resolution in space and time was greatly improved.Under mechanical force,the UTDI-3/ZnS emit different chemiluminescent signals,indicating the process before and during covalent bond scission in the entire damage course of the material,which provide more comprehensive and sensitive information for detecting polymeric materials'failure.