Design,Synthesis And Optical Properties Regulation Of Mechano-Responsive Elastomers And Hydrogels

Polymer mechanochemistry,as an emerging subject to facilitate chemical transformation by mechanical force,provides insights into the relationship between microscopic chemical bond scission events and macroscopic mechanical properties of materials.In recent years,mechano-responsive polymers for bond scission visualization have attracted much attention due to the easy detection and quantitative comparison of optical signals,and have broad application prospects in fields of material damage detection,stress sensing,self-healing and drug release.In order to design functional materials with a wider range of mechanical force response and higher response sensitivity,this thesis focuses on the development of new mechano-responsive elastomers and hydrogels by expanding the application systems of 1,2-dioxane and adjusting the optical properties as well as developing the novel mechanophores.The detailed studies are presented as follows:1.To expand the application range of 1,2-dioxetane,a ultrastrong and tough mechanoluminescent hydrogel was designed and synthesized by covalently incorporating 1,2-dioxetane into the main chain of linear polyurethane containing multiple ureas groups.Based on this ingenious design,a highly spatio-temporal sensitive visual detection of the stress distribution damage failure mechanism in polar materials was realized.Besides,the effects of hydrogen bond contents,water content and strain rates on the mechanoluminescent properties of polyurethane hydrogels were systematically studied,which will help us to have a deeper understanding of the mechanism of mechanical energy conduction and damage in the hydrogel system,as well as expand the application of 1,2-dioxetane in the field of biomedicine.2.To regulate the optical properties of 1,2-dioxetane,a transparent mechanical force induced red emission elastomer film with Eu（TTA）₃（Aphen）as the acceptor was designed and synthesized based on the efficient energy transfer strategy between Eu（III）complex and the excited state adamantanone produced by the cleavage of 1,2-dioxetane.The covalently incorporation of Eu（TTA）₃（Aphen）acceptor can not only maintain the mechanical properties and transparency of the polymer film,but also change the color and improve the temporal and spatial sensitivity of mechanoluminescence,which is very important for in-situ study of material damage mechanism.In addition,a stretch-induced patterned red emission flexible device with the polymer film as an emissive layer was fabricated,which highlight the potential applications of these polymers in the failure detection and stress mapping of smart flexible devices and provides a new idea for the development of highly sensitive stress sensors.3.In order to extend the luminescence wavelength of mechano-responsive hydrogels to the near infrared region,a novel mechanophore Rh-Co based on coumarin-semirhodamine and the corresponding mechano-responsive micellar hydrogels were developed.These hydrogels undergo opening of the rhodamine structure and exhibit high-contrast color changes from yellow to green and highly penetrated near-infrared（NIR）fluorescence emission under different types of mechanical forces（tension,pressure,and friction）.The change of the optical signal is related to the force,which lays the foundation for the quantitative characterization of the stress in the hydrogel.In addition,the dual stimuli-responsive characteristics to force and acid of the hydrogels provided access to a multi-mold and highly efficient way for data encryption and decryption.4."Flex-activation"is a new way to realize the force-induced release of small molecules in the polymer network,which mainly realizes the mechano-chemical reaction through the bending of the bond angle of the mechanophore.In order to realize the visualization of force-induced release of small molecules,a new type of mechanophore An-DA based on the Diels-Alder cyclo-addition product of anthracene and alkyne was designed and synthesized.Whether in the crystal state or as a cross-linker,the An-DA can leverage bond bending to facilitate the occurrence of the reverse Diels-Alder reaction,accompanied by the release of anthracene,which displays the characteristic fluorescence emission.Besides,the effects of compression stress and crosslinking density on the release of anthracene were systematically studied,which proved that the mechano-responsive properties of An-DA.In addition,the linear PMA containing An-DA do not have mechano-responsive behaviors by ultrasound sonication,indicating that the mechanical force activation mechanism of An-DA is“flex activation”.In short,the An-DA mechanophore regulates the optical properties of the“flex activation”mechano-responsive system and has great potential applications in the fields of biological detection and drug release.