Synthesis And Characterization Of Azo Liquid Crystalline Polymer Containing Two Chiral Units

Chiral liquid crystalline polymers(CLCPs)which combine the function of chiral material and azo group are important optical materials,exhibiting several promising properties like good optical properties,mechanical properties,easy processing,high thermal stability and so on.Azobenzene molecules exist cis-trans isomers phenomenon,the introduction of azobenzene molecules into the liquid crystal elastomer can form azo liquid crystal elastomer,azo liquid crystal elastomer not only has the properties of azo liquid crystal polymers,but also has the properties of network Polymers like excellent mechanical properties,high temperature,chemical resistance and so on,which is one of the important researchs of flexible materials.In this paper,one kind of cholesteryl liquid crystal monomer S,one kind of liquid crystal monomer containing cyano Q and two kinds of single phenol monomers W,X and one kind of azo liquid crystal monomer H were synthesized.At the same time,the ASQ series were synthesized by S,Q and W,the BSQ series were synthesized by S and W,and the DSQ series were synthesized by S and X.The ASZ and BSZ series were synthesized by ASQ and BSQ with azo liquid crystal monomer H,The CSZ series were synthesized by BSQ with azo crosslinking agent N and P-Fluorobenzoyl chloride.DSZ series were synthesized by DSQ with crosslinking agent adipyl chloride and azo liquid crystal monomer H.Some conventional experimental analytic techniques were used to comfirm the chemical structures and liquid crystal properties of monomers and polymers such as FTIR,POM,DSC,XRD and ultraviolet-visible,showing that the structures were in line with the molecular design.From the UV-Vis,contrasted to their precursor polymers ASQ and BSQ series,the azo polymers ASZ and BSZ had azo absorption peaks at 350 nm and 455 nm.The azo absorption peaks increased with the proportion increasing of the azo monomer.Under the light,phenomenon of cis-trans isomerization happened.However,the polymer would return to the original state when light was stopped.It showed that two series of azo polymer had photochromic properties.By DSC curve,all the heating and cooling curve of liquid crystal monomers appeared melting point and clear point.The heating curves of all the polymers appeared obvious glass transition temperature.As the change of composition,the Tg of ASQ,ASZ and BSQ decreased gradually,the Ti decreased too;the Tgof BSZ decreased first and then increased;Ti decreased gradually;the Tg of CSZ decreased first and then increase,the Ti decrease;the Tg of DSQ decreased first and then increased,Ti decreased gradually;the Tg and Ti of DSZ decreased first and then increased.From the POM,the four liquid crystal monomers have obvious texture features.Q and N were nematic liquid crystal monomers,H and S were cholesteric liquid crystal monomers.The seven series polymers had wide temperature range of liquid crystal phase,whose liquid crystalline property were manifested on the special color texture,indicating that all the polymers are thermotropic liquid crystalline polymers.The seven series of polymers belong to cholesteric liquid crystal.By optical analysis,precursor polymers ASQ series were right-handed optical active substances,but azo liquid crystal polymer ASZ series were left-handed optical active substances for having the different chiral group,BSQ and BSZ series were left-handed optical active substances,however,the values of specific rotation increased than BSQ series.From the swelling experiments,the average molecular weight(Mc)of CSZ and DSZ series between the crosslinking points is lower,the azo liquid crystal elastomer crosslinking density(Me)is greater,with the increasing of crosslinking degree.From XRD,respectively,for All polymer series,the reflection peak in the small angle did not appear,which could be deduced that the polymers did not have smectic layers,but broad peaks appeared at 20?15.90-17.100(d=5.57-5.49 A).The high d values were in accordance with the regular pattern of the cholesteric polymer,which was ascribed to the rotation of the cholesteric group,revealing that the all polymer series were in the cholesteric phase.