Synthesis And Properties Of Novel Chiral Side-Chain Liquid Crystalline Elastomers Containing Dimer Type Monomers

Liquid crystalline elastomers(LCEs)are a kind of rubber like materials formed by liquid crystal polymers after crosslinking.They combined the active orientational properties of the liquid crystals with the good stretching abilities of rubber,endowing LCEs with excellent optical,thermodynamical and mechanical behaviors.The chirality in Liquid crystalline elastomers can be at the origin of additional physical properties such as ferroelectricity,pyroeletricity,circular dichroism,and nonlinear optics coupled to the polymer network.Applying external mechanical fields to the elastomers consequently causes electromechanical and optomechanical effects that do not exist in conventional low molar mass liquid crystals or conventional isotropic polymer networks.Especially as the ideal materials for pyroelectric applications,they can effectively reduce the disturbance from the flowing of the conventional low molar materials.Chiral liquid crystalline elastomers(ChLCEs)therefore presently become one of the frontier directions in the study of liquid crystal polymers(LCP)systems.The molecular design,structure and performance of liquid crystalline elastomers,as well as their applications in high technical field are the two main research directions in the study of LCEs.In the present dissertation,based on the previous study of the same research group,the chemical structures and synthesis methods of the liquid crystalline elastomers were further explored.Totally nine kinds of new chiral and non-chiral dimer type monomers with excellent liquid crystalline performance were synthesized,three kinds of diene type liquid crystal crosslinkers with different chainlengths were prepared,five sets of novel chiral liquid crystalline elastomers based on the monomers and crosslinkers thereof were polymerized.Which may provide new concept and theory evidence for the futher design and synthesis of chiral liquid crystalline elastomers with special performance,meanwhile offer more choices for the research of the applications of chiral liquid crystalline elastomers.According to the different mesogenic groups at the polymerization side,the nine kinds of chiral and non-chiral dimer-type liquid crystalline monomers can be divided into allyloxybenzoic acid phenolic ester type(M1-1?M1-3),allyloxybenzoic acid biphenol ester type(M2-1-M2-3)and undecenyl biphenol ester type(M3-1?M3-3).Among them,the chiral monomers first introduced the(S)-2-octanol as the chiral center and achieved very good liquid crystalline hehaviors.The terminal groups of non-chiral monomers were all cyano groups,which greatly extended the liquid crystal phase of monomers.Three kinds of symmetric diene type liquid crystal crosslinkers(CL1-CL3)were designed and synthesized.The molecular length and complexity of the liquid crystal crosslinkers were increased with the increasing numbers of benzene rings and ester groups.The gradually increased chiral rotation trend and the presentation of the chiral liquid crystal phase which were usually not existed in such structures were observed.The occurrence of this phenomenon has been analyzed and explained theoretically.Through the copolymerization of chiral and non-chiral monomers and crosslinkers with good liquid crystallinity and similar temperature ranges,five series of polysiloxane type chiral liquid crystal elastomers(E1-E5)were obtained respectively.These five series of elastomers were all synthesized from one chiral monomer,one non-chiral monomer and one liquid crystal crosslinker,which were similar in the temperature ranges of liquid crystal phases,in order to obtain better liquid crystal properties.The structure and properties of the synthesized liquid crystal monomers,crosslinkers and liquid crystal elastomers were studied by FT-IR,IH NMR,DSC,TGA,polarimeter,POM,X-ray and three-dimensional infrared analysis(3D FT-IR).The theoretical molecular lengths of monomers and crosslinkers were calculated by Material Studio 6.0,a chemistry computational software.The effective crosslinking densities of the elastomers were calculated by the swelling tests for the polymers.The crosslinking densities represented the crosslinking quality of the elastomers.The experimental and testing results showed that:1.All of the nine dimer type liquid crystal monomers were tautomeric liquid crystalline compounds.The non-chiral liquid crystalline monomers exhibited a variety of textures such as smectic A phase,smectic C phase and nematic phase,etc.;While the chiral liquid crystalline monomers showed a variety of chiral texture such as chiral smectic phase and chiral nematic phase.The three types of liquid crystal monomers showed differences in the temperature ranges of liquid crystalline phases due to the differences in their chemical structures.The phase changes of the liquid crystal monomers were basically symmetrical during the temperature rising and falling cycles.2.All of the three liquid crystal crosslinkers were tautomeric liquid crystal compounds,with the increase of benzene ring and ester groups,certain levels of optical activities were emerged,a trend of forming chiral smectic phases was also observed.This was due to the increase of the benzene rings and the ester groups made the molecular structures of the crosslinkers twisted and rotated more easily,while the long molecular length made them only present chiral smectic phases rather than chiral nematic phases.3.All of the five series of ChLCEs exhibited rich chiral liquid crystal phase textures,such as chiral smectic C phase and cholesteric phase;all of which had wide range of liquid crystalline phases and high thermal stability.The relationship between the molecular composition of liquid crystal monomers and crosslinkers,and the structures and properties of the liquid crystal elastomers was studied.The influence of the composition of liquid crystal elastomers and the contents of crosslinkers on the properties of liquid crystal elastomers was also discussed.