Mechanochromic And Mechanochemiluminescent Polymeric Materials:Design,Synthesis And Properties

It is of great significance to study the breakage of chemical bond,which is closely related to the damage of polymeric materials,at a microscopic level.Mechanoresponsive polymers are promising candidates for a variety of potential applications,such as damage detection and self-strengthen of materials,catalysis,controllable release of chemicals.Aimed at developing mechanochromic and mechanoluminescent polymers,this thesis reported the design,synthesis and property investigation of materials containing classical mechanophores and a series of new mechanophores.The results can be summarized as follows:1.To further understand the stress damage process of polymer nanocomposites,the classical mechanochemiluminescent unit,1,2-dioxtane,was covalently introduced into the PU/PEMA semi-interpenetrating network(semi-IPN)filled with Janus nanoparticles(surface modified amino and hydroxyl groups)and a series of hierarchically crosslinked composites were prepared.The in-situ characterization of mechanoluminescent process revealed that the mechanical properties of the semi-IPN can be significantly improved by filling Janus nanoparticles.Benefit from 1,2-dioxetane as an optical built-in probe,the fracture of covalent bond and the information of stress distribution in the material can be obtained visually.This work expands the application of Janus nanoparticles and develops a new way to study the polymer nanocomposite.2.It is of great significance to monitor the stress and deformation of materials in a broader range of time and force.In this chapter,we covalently introduced two distinct complementary mechanophores,i.e.,rhodamine and 1,2-dioxetane,into polymer blends to obtain a series of composite materials with both discoloration and luminescence.The in-situ characterization of mechanochromic and mechanoluminescent processes,combined with fluorescence resonance energy transfer strategy,found that rhodamine took precedence over 1,2-dioxetane in bond breaking,which together endows the material with a broader force threshold range.This work not only verified the relative magnitude of the force threshold of two distinct mechanophores by experiments,but also realized the multi-mode stress monitoring of elastomers.3.To improve the sensitivity of rhodamine-based mechanophore and study the relationship between structure and mechano-responsive behavior,cyclization and structural isomerization was considered to control the magnitude and direction of force at the molecular level.With that in mind,polymethyl acrylate(PMA)containing aminobenzopyranoxanthene with two spiro rings(ABPX)was synthesized and proved to have mechano-responsive behaviors by ultrasonic experiments.Meanwhile,the influence of structural isomerism and stereoisomerism on the mechano-responsive behavior was also verified.By means of single molecule force spectrum,the successive ring-opening of ABPX was proved.Moreover,due to the introduction of two mechanoresponsive sites on one mechanophore,the force threshold can be regulated easily.4.On the basis of the third work,in order to achieve the collaborative control of optics and mechanical response of rhodamine-based structure at the molecular level,we further expanded the structure of ABPX.According to the same cyclization strategy,two rhodamine molecules were fused to synthesize the bis-rhodamine.By SET-LRP,the mechanophores were covalently introduced into polymers and a series of PMA containing mechanophore in the middle of polymer chain was prepared.The mechanoresponsive behavior was proved by ultrasonic experiments and the influence of positional isomerism on the mechano-responsive behavior was also verified.Besides,compared with rhodamine as mechanophore,it is proved that the mechano-responsive color can be modulated by the π-conjugation degree of mechanophores.This work further enriched the family of rhodamine-based mechanophores and developed a new method to change the mechanochromic behavior of rhodamine-based molecules.