| The design of new types of liquid crystal compounds and liquid crystalline polymers has become the mainstream research direction,with the continuous deepening of liquid crystal chemistry exploration.The multi-arm liquid crystal compound is a new type of liquid crystal material,which connects a number of liquid crystal arms to the central atom or group.The liquid crystalline compound of azobenzene with cholic acid as the center has the azo material characteristics of the photoisomerization.Because of the existence of the chiral center of cholic acid,the molecule exhibits a helical structure,which makes it easy to improve its liquid crystalline properties.This new type of liquid crystal macromolecule is different from the traditional rod like liquid crystal compounds,and with the different substituents at the end,there will be rich and colorful liquid crystal phase.Through reading many literatures,five kinds of long chain azo liquid crystal arms with different substituents were designed and synthesized,and the multi arm azobenzene liquid crystalline macromolecules were prepared by esterification.Five kinds of liquid crystalline macromolecular monomers with cholic acid as the center were synthesized and introduced into the flexible polysiloxane backbone to synthesis a new side-chain liquid crystal polymer.The first part is about the synthesis and properties of azobenzene liquid crystal arms.We designed and synthesized mesogenic arms where the 4-position at one end consisting different terminal substituent,4-nitroazobenzene(A1),4-chlorineazobenzene(A2),4-azobenzene(A3),4-methylazobenzene(A4),4-methoxyazobenzene(A5),and five kinds of long chain liquid crystal arms were prepared by esterification reaction with adipic acid,4-nitroazobenzene alkyloxyethyl formyl pentanoic acid(B1),4-chlorine-azobenzene alkyloxyethyl formyl pentanoic acid(B2),4-zobenzene alkyloxyethyl formyl pentanoic acid(B3),4-methylazobenzene alkyloxy ethyl formyl pentanoic acid(B4),4-methoxyazobenzene alkyloxyethyl formyl pentanoic acid(B5).The LC arms conformed to the molecular design on the structure,were characterized by FT-IR and 1H-NMR.Liquid crystal properties were characterized by DSC and POM,it showed that liquid crystal arms B1,B2,B4,B5 were thermotropic nematic phase liquid crystal type,displayed texture of schlieren.The range of the liquid crystal between 20-35? on heating process,the wide range of liquid crystal in the 40-80? on cooling process.The results of B1-B3 indicated that Tm decreased with the polarity of the terminal groups of the mesogenic arms decreasing.The results of B3-B5 also showed the similar change trend,which Tm of B3-B5 increased with the polarity of the terminal groups of the mesogenic arms increasing.The Ti of the liquid crystal arm agreed with this rule.UV-Vis analysis showed that the five kinds of liquid crystal arms appeared photoinduced isomerization,and with the increase of UV irradiation time,the molecules would change from trans to cis,and with the increase of time,the ratio of cis to trans tended to be stable.The second part,The three arms liquid crystal macromolecule(C1-C5)and four arms liquid crystal macromolecule(D1-D5)were prepared by esterification with cholic acid as the chiral center.The LC arms conformed to the molecular design on the structure,were characterized by FT-IR and 1H-NMR.Liquid crystal properties were characterized by DSC and POM,it showed that three arms liquid crystal macromolecule C1,C2,C4,C5 were thermotropic cholesteric phase liquid crystal type,displayed texture of fingerprint texture.The range of the liquid crystal between 30-40? on heating process,the wide range of liquid crystal in the 40-70? on cooling process,four arms liquid crystal macromolecule D1,D2,D4,D5 were thermotropic cholesteric phase liquid crystal type,displayed texture of fingerprint texture.The range of the liquid crystal between 30-40? on heating process,the wide range of liquid crystal in the 40-50? on cooling process.Both the three arms macromolecular C3 and four arms macromolecular D3 have no liquid crystalline property during heating and cooling process.The results of C1-C3 indicated that Tm decreased with the polarity of the terminal groups of the mesogenic arms decreasing.The results of D3-D5 also showed the similar change trend,which Tm of D3-D5 increased with the polarity of the terminal groups of the mesogenic arms increasing.The Ti of the liquid crystal arm agreed with this rule.UV-Vis analysis showed that The three arms liquid crystal macromolecule(C1-C5)and four arms liquid crystal macromolecule(D1-D5)appeared photoinduced isomerization,and with the increase of UV irradiation time,the molecules would change from trans to cis,and with the increase of time,the ratio of cis to trans tended to be stable.In the third part,we designed and synthesized liquid crystal monomers(M1-M5)and liquid crystal polymer PM1-PM5 was synthesized by copolymerization of M1-M5 and methyl hydrogen siloxane(PMHS).The monomers M1-M5 and the polymer were analyzed by IR,result were conformed to the molecular design.Liquid crystal properties were characterized by DSC and POM,it showed that liquid crystal monomers were thermotropic cholesteric phase liquid crystal type,displayed texture of fingerprint texture.The range of the liquid crystal between 30-50? on heating process,the wide range of liquid crystal in the 60-110? on cooling process.In addition to the liquid crystal monomer M3,there is no liquid crystal during the process of heating and cooling.From the polymer liquid crystal performance analysis,The PM1,PM2,PM4 and PM5 series of polymers exhibit different liquid crystal phases with the change of monomer content.When the monomer content is small,the Grandjean texture appears,and when the ratio of monomer is relatively high,the texture of the oil filament appears.From the DSC curves of polymers,the glass transition temperature and the clearing point temperature decreased gradually with the increase of monomer content,the PM3 series of polymers do not have liquid crystalline property. |
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