Design,Synthesis And Properties Of Novel Hemiphasmidic Side-Chain Fluorescent Liquid Crystalline Polymers

In this paper,the construction of fluorescent liquid crystal polymer material with AIE properties and rich self-assembly structures is taken as the starting point.The classical AIE group:cyanostilbene was introduced as a rod-like rigid core into the hemiphasmidic side-chain liquid crystal polymers(SCLCPs)system and a series of hemiphasmidic SCLCPs with different chemical structures were designed and synthesized.The effects of the number and the length of tail chains,the length of the flexible spacers and the conjugation effect of the rigid core on the phase structure,phase behavior and fluorescence properties of this novel type of hemiphasmidic side-chain fluorescent liquid crystal polymers(SCFLCPs)were investigated.The understanding of the self-assembly behavior of hemiphasmidic SDFLCPs was deepened,and the nature of AIE phenomenon was discussed in depth.At the same time,the application of hemiphasmidic SCFLCPs containing cyanostilbene in photoresponsive liquid crystal elastomer was discussed.The main research work of this paper are as follows:(1)A novel series of SCLCPs containing cyanostilbene with different number of tail chains(P1-8C,P2-8C and P3-8C)were first reported and synthesized via conventional free radical polymerization.The self-assembled structure and fluorescence properties of the polymers have been investigated by DSC,POM,1D WAXD,SAXS,UV-vis spectra and PL emission spectra.The results revealed that the number of alkoxy tail chains was critical to the fluorescence properties and self-assembly behaviors of this type of liquid crystal polymers.As the number of terminal alkoxytail chains increases,the phase structure of the polymer translates from a smectic phase to a hexagonal columnar phase.Meanwhile,the AIE characteristics and solid-state fluorescence quantum yield of the polymer also increase as the number of alkoxy tail chains increases.(2)A series of hemiphasmidic SCFLCPs containing cyanostilbene with different lengths of side chains,denoted as P3-mC(m=2,4,6,8,10,12,which stands for the number of the carbons of the alkoxy chains)were synthesized via conventional free radical polymerization.The self-assembled structure and fluorescence properties of the polymers have been investigated by DSC,POM,1D WAXD,SAXS,UV-vis spectra and PL emission spectra.The results revealed that the the spatial effect caused by the length of the alkane tail chain has a very significant influence on the supramolecular self-assembly structures and fluorescence properties of this type of fluorescent liquid crystal polymer.When m=2,4 and 6,the polymers tended to rely on the orientation arrangement of the rigid rod-like mesogen in the side groups to form a smectic phase structure;as the length of the tail chain increased,the self-assembled structure of the polymer transforms to hexagonal columnar phase which constructed by the side group and the main chain.All polymers exhibited a significant AIE effect,however,the fluorescence quantum yield of P3-mC in the solid state increased with the length of the alkane tail chain.(3)A series of hemiphasmidic SCFLCPs containing cyanostilbene with different lengths of flexible spacers,denoted as Pr-n(n=2,4,6,8,10,which stands for the number of the carbons of the flexible spacers.)were synthesized via conventional free radical polymerization.The self-assembled structure and fluorescence properties of the polymers have been investigated by DSC,POM,1D WAXD,SAXS,UV-vis spectra and PL emission spectra.When the flexible spacer is short(n=2 and 4),the polymer self-assembles to form a hexagonal columnar phase;further increasing the length of the flexible spacer(n=6,8,10),the phase structure of the polymer is converted to the Sm phase.Although Pr-n exhibits a similar AIE effect,the solid fluorescence quantum yield of Pr-n decreases as the length of the flexible spacer increases.(4)A series of hemiphasmidic side chain fluorescent liquid crystal polymers(PE-8C,PB-8C and PA-8C)with different rigid cores were synthesized via conventional free radical polymerization.The results reveal that the three polymers can self-assemble to form a hexagonal columnar phase,however,their clearing points are much higher than P3-8C.On the other hand,since the different internal connections can change the conjugated system of the rigid core,the fluorescent colors of the polymers are quite different.(5)The novel liquid crystal elastomer LCEs-HE were successfully synthesized by copolymerization of hemiphasmidic mesogen monomer and multiple hydrogen bond crosslinkers.The results of liquid crystal properties of LCEs-HE showed that the introduction of a small amount of cross-linking agent UPy transformed the copolymer'phase stucture from a hexagonal columnar phase structure of homopolymer to smectic phase structure.The results of the light responsiveness study of LCEs-HE indicated that LCEs-HE could undergo a Z/E configuration transition under ultraviolet light,which caused a change in fluorescence color.At the same time,the irradiation of ultraviolet light could also cause a large deformation of the single domain oriented fibers of LCEs-HE,indicating that LCEs-HE was a novel kind of liquid crystal elastomer having excellent photodeformation ability.