Architecture Design Of Spiropyran-contained Elastomer And Its Mechanochromic Behavior

Mechanochromic polymers are species that change their color in response to mechanical stress.Such materials hold great promise for applications such as stress and strain sensing,information storage and structural health monitoring.In this project,a novel strategy was employed for incorporating mechanophores into the interfaces of polymeric materials.Comb or star shaped copolymers were produced possessing mechanophore linking incompatible polymer chains,which required the design and generation of novel asymmetrical spiropyrans.The mechanochromic polymers generated show distinct color changes,which are both quite sensitive and repeatable,in response to applied loads.Work involved the development of four spiropyran compounds containing two different polymerizable groups.These were utilized as the grafting point in the generation of comb-shaped poly(butylacrylate)-polystyrene(PBA-b-PS)graft copolymer using a two-step control/"living" polymerization.The influence of polymer structure and composition on the microscopic morphologies and mechanochromic behaviors were investigated.In addition,a novel comb-shaped poly(butylacrylate)-poly(methyl methacrylate)(PBA-b-PMMA)graft copolymers with spiropyran as the grafting point and pendant nitrobenzoxadiazole(NBD)in the PMMA side chains were customer-made for which the influence of polymer composition on the mechanoluminnescet and photoluminescent behaviors were investigated.Finally,a star copolymers(HBPE-s-PS)possessing hyperbranched polyethylene(HBPE)cores,polystyrene(PS)arms and spiropyran linkages were developed.The star copolymers were blended with polystyrene-poly(ethylene/butylene)-polystyrene(SEBS)and the mechanochromic behaviors of their films were investigated.The major achievements of this thesis include:(1)The design of several asymmetrical functional spiropyrans,making their incorporation at the interfaces of polymeric materials possible through a newly developed,high-yield synthetic route.(2)The synthesis of a mechanochromic comb-shaped copolymer PBA-b-PS,which exhibits the characteristics of a thermoplastic elastomer.Spiropyran groups are located at the interface of the polymer,enhancing the transmission of applied loads.This lowers the relative discoloration strain threshold of the copolymer producing a more sensitive response.It was determined that increasing the PS content and/or decreasing in the number of PS side chains increases the breaking strength of the copolymer,lowers the discoloration strain threshold,and enhances the force-induced discoloration(3)Synthesis of mechanoluminescent comb-shaped copolymer.PBA-SP-P(MMA-co-NBD),demonstrating fluorescence resonance energy transfer(FRET).Spiropyran groups are the branching points,and the fluorescent NBD donor groups are pendant onto the PMMA side chains.This places the spiropyran at the interface and NBD inside the dispersed PMMA domains.The distance between NBD and spiropyran was maintained at less than 10 nm by adjusting the length of PMMA side chains,which satisfies the requirement of FRET.The energy transfer efficiency in the copolymer films after UV excitation was greater than 65%.The energy transfer efficiency could be increased by reducing PMMA content,while NBD content was shown to have little influence.(4)Development of a mechanochromic star copolymer(HBPE-SP-PS)with spiropyrans as the connection between the HBPE core and PS arms.The star copolymer was blended with SEBS to construct a mechanochromic elastomer possessing a relatively low discoloration strain threshold of?75%.The force-induced discoloration performance was shown to decrease in cyclic tension.