Main Chain Liquid Crystalline Elastomers Via Thiol-ene Photopolymerization

In recent years,liquid crystal elastomer has become another practical material in the field of liquid crystal materials.Click chemistry has the advantages of controllable reaction and high efficiency,which can be used to prepare the main chain and side chain liquid crystal elastomers.Therefore,in this paper,the main chain liquid crystal polymer and liquid crystal elastomer were prepared by thiol olefin click chemical reaction of diene monomer and 1,6-hexadithiol(DMH)with 2-hydroxy-2-methylphenylpropane-1-one(HDMPH)as photoinitiator and pentaerythritol-3-mercaptopropionate(PETMH)as crosslinker.The results of ~1H NMR and IR,DSC and polarizing microscope also show that the liquid crystal monomer is pure.The click chemical reaction between thiol and crosslinker and the self synthesized diene liquid crystal monomer can be carried out smoothly,and the corresponding"soft"and"hard"chain segment regular interphase arrangement polymer can be obtained.The results of differential scanning calorimetry(DSC),polarized light microscopy(PLM)and wide angle X-ray diffraction(WAXD)show that the main chain polymer and elastomer have a liquid crystal transition point and a typical texture,which is a typical main chain nematic liquid crystal.Two groups of main chain liquid crystals and their elastomers were made according to whether to add photoinitiator or not.The GPC and the film forming experiment of the reaction process showed that when the photoinitiator was added to the reaction system,the main chain liquid crystals and their elastomers had higher molecular weight,good film forming performance and good mechanical properties,while those without photoinitiator were used In the reaction system,the molecular weight of the polymer is low,the film forming property is poor,and the film is brittle fracture.Compared with the uncrosslinked liquid crystal polymer,the crosslinked main chain liquid crystal elastomer obtained by thiol ene click reaction has higher heat resistance,glass transition temperature and melting point.After rapid cooling by hot stretching,the liquid crystal elastomer film changes from a non transparent multi domain structure to a transparent single domain structure,while the samples without hot stretching can only obtain a multi domain structure.