Synthesis And Properties Of Novel ?-cyanostilbene Based Photodeformable Liquid Crystalline Elastomers

In recent years,azobenzene based photodeformable liquid crystalline elastomer(LCE)materials have developed vigorously for their promising applications ranging from flexible robots,organic actuators,and artificial muscles,to micro-mechanical system and intelligent dynamic interfaces.However,there are some deficiencies in the practical application,for example,the deformation cannot maintained long in visible light environment due to the poor thermodynamic stability,and the deformation speed is generally slow.The synthesis of azobenzene usually has a low conversion rate for the limitation of the synthesis conditions.Thus there is an urgent need to seek out new chromophores other than azobenzene and discover new mechanisms to compensate for the defects of azobenzene based liquid crystal elastomers.This thesis is focused on the influences of liquid crystalline(LC)phase behavior and phase structure on the photoresponsive properties of side chain liquid crystalline elastomers(SCLCEs).Design and synthesis a series of novel ?-cyanostilbene-based SCLCEs,which cross-linked by multiple hydrogen bonds,with different length of flexible spacers,different ?-cyanostilbene(CS)contents and different steric hindrance were first carried out.Through the research,the effects of the length of the flexible spacer,the introduction of biphenyl mesogens and the steric hindrance effect on LC phase behavior and photodeformation behavior of CS-based SCLCEs were obtained,which will be useful for the preparation of CS-based photodeformable SCLCEs with superior properties.In addition,In addition,a series of CS-based liquid crystalline supramolecular polymers were prepared by hydrogen bond supramolecular self-assembly.The relationships between the LC phase structure and photodeformation properties of liquid crystalline supramolecular polymers were systematically investigated.The photodeformation mechanism and its practical applications in the field of information encryption were also explored.The main research results of this thesis are as follows:(1).A series of CS-based SCLCEs(LCE-mCS,(m=0,2,4,6,8,10))which cross-linked by multiple hydrogen bonds with different lengths of flexible spacers were successfully synthesized by conventional free radical polymerization.The research results showed that all the LCE-mCS samples formed smectic phase and the clearing temperature(Ti)tended to decrease first and then increase with the increasing spacer length.Photobending study results showed that under UV irradiation,the uniaxially oriented LCE-mCS fibers can bent toward the light source along the fiber axis and their maximum bending angles and bending speed increase with the increasing length of the spacer.The study on the deformation mechanism of liquid crystalline elastomer showed that the Z/E isomerization of CS mesogens and their photothermal effect act together on the deformation of the fiber,and the two mutually promote each other,which gives excellent photodeformation properties of LCE-mCS fibers.(2).A series of hydrogen bonded crosslinked CS-based SCLCEs(CSm-BPn(m:n=0:5,1:4,2:3,3:2,4:1,5:0))with different CS contents were successfully synthesized via conventional free radical polymerization.The DSC,POM,and 1D WAXD results showed that all the CSm-BPn samples formed smectic phase.With the introduction of biphenyl mesogens,both Tg and Ti of CSm-BPn(m:n=1:4,2:3,3:2,4:1)showed some extent of decrease due to the structural differences between?-cyanostilbene and biphenyl.The photoinduced bending experiments showed that CS0-BP5 has no photodeformation behavior due to the absence of cyanostilbene groups.Compared with CS5-BP0,both the maximum bending angle and the bending speed of CSm-BPn(m:n=1:4,2:3,3:2,4:1)increased greatly as the he introduction of biphenyl mesogens,especially,for CS3-BP2 and CS2-BP3 are the most significant.Through the research in this chapter,the deformation mechanism and influencing factors of CS-based photoresponsive LCEs have been understood more deeply and comprehensively.(3).A series of hydrogen bonded crosslinked CS-based SCLCEs:LCE-o(m,p)CS,with different steric hindrance were successfully synthesized through conventional free radical polymerization.The LC phase behavior and phase structure of LCE-o(m,p)CS were carefully studied via DSC,POM,and 1D WAXD.The results showed that LCE-oCS cannot form LC phase due to great steric hindrance effect.For LCE-pCS and LCE-mCS,the stability and order degree of the LC phase decrease with the increasing steric hindrance effect.It's found that both the maximum bending angle and the bending speed of uniaxially oriented LCE-o(m,p)CS fibers were greatly reduced with the increasing steric hindrance effect,which is attributed to the destruction of the order degree and stability of the LC phase by steric hindrance.In addition,compared with LCE-OCS in Chapter 2,it is found that both the photoisomerization behavior and photodeformation properties of LCE-pCS are better than that of LCE-OCS due to the plasticization of the alkane tails in LCE-pCS.In combination with the excellent liquid crystallinity of the non-flexible spacer side chain liquid crystal polymer and the rapid photoresponsiveness of cyanostilbene,a polymer material with excellent light stimulation-response deformation properties was obtained.(4).A series of supramolecular polymers:P4VP(Z-TCS)x,have been successfully prepared through hydrogen-bonding interaction by introduceing(Z)-2-(4-hydroxy-phenyl)-3-(3,4,5-tris(dodecyloxy)phenyl)acrylonitrile(Z-TCS)into P4VP matrix via solution blending method.All the supramolecular polymers exhibit liquid crystallinity at room temperature,wherein P4VP(Z-TCS)1.0 appears as hexagonal columnar phase,and the others display smectic phase.P4VP(Z-TCS)fibers showed excellent photoinduced deformation ability under UV irradiation both in terms of bending speed and bending angle.Similar to azobenzene,the surface layer of P4VP(Z-TCS)x fibers absorbs most incident photons leading the uneven contraction which caused by the combination of the order-disorder phase transition of ?-cyanostilbene mesogens and contraction of P4VP backbone.In addition,benefit from the uneven distribution of Z and E-cyanostilbene isomer along the radial direction of the fibers and the stability of E-TCS isomer,the shape forming by UV irradiation can be eliminated by external stretching force and recovered under heating.Therefore,the P4VP(Z-TCS)x fibers can be used in information encryption realm and orther smart manufacturing materials.