Synthesis And Characterization Of Side-chain Bent-core Liquid Crystalline Polymers With Photo-active Azo Linkages

Banana-shaped liquid crystalline polymer is a new type of liquid crystalline material, itcombines the special properties of liquid crystals and the outstanding mechanical andprocessing properties of polymers, which gives it numbers of special properties, such as (anti)ferroelectricity, spontaneous polarization, forming chiral supramolecular structure and soon.Therefore such liquid crystalline materials have a very wide application prospect. What’smore, the azobenzene(azo) polymers have the properties of photoresponsive, photochromic,non-linear optics and so on, which makes azo polymers become a new type of photoelectricityfunctional material. In this article, we tried to introduce azo group into bent-core liquidcrystals, then synthesized side-chain azobenzene liquid crystalline polymers by differentmeans, expecting to get a new kind of material, which has the photoresponsive properties ofazobenzene compounds and the outstanding properties of liquid crystalline polymers.Firstly, six bent-core liquid crystalline compounds were designed and synthesized, that is,an azobenzene liquid crystalline monomer MC without any active double-bond; threeazobenzene liquid crystalline monomers MA8, MA10, MA12with acrylate as activedouble-bond and different alkyl chains; two azobenzene liquid crystalline monomers havingdifferent amount of vinly groups(MB1, MB2), respectively. In molecule design, these threetypes of compounds both used the m-aminobenzoic acid as the bent unit, and introduced azogroups, Schiff base as the connecting groups. These monomers were characterized by1HNMR,13CNMR, Infrared absorption spectrum (IR) and element analysis to confirm their structures.Then their thermodynamics behaviors and liquid crystalline properties were studied bydifferential scanning calorimeter (DSC), polarizing optical microscope analysis (POM) and1D wide angle X-ray diffraction analysis (1D-WAXD).The results showed that monomer MChad B2phase, the liquid crystalline behaviors of the monomer MA8, MA10, MA12disappered after introducing acrylate group, and the monomer MB1, MB2kept their B2phasewhile MB2had a higher LC phase transition temperature and lower crystalline phasetransition temperature comparing with MB1. The photoresponsivity of the monomers were also confirmed by UV-Vis absorption. All the monomers had a similar Uv-Vis absorptionspectrum. The peaks of theirUV absorptions were all in about350nm, which refered to π－π＊electricity transition of azo group with trans-form. And the peaks of the Vis absorptions wereall in about450nm of azo group with cis-form, which related to the n－π＊electricity transiton.After induced by UV light, it could be observed that their peaks of π－π＊transitionabsorption became weaker and almost disappear while their peask of n－π＊transitionabsorption became stronger, so it was obvious that all the monomers had the photoresponsityproperties.Secondly, three side-chian bent-core liquid crystalline polymers were synthesized byradical polymerization of MA8, MA10, MA12, which were differed from their length ofspacers. Structures and molecular weight of the polymers were characterized by1HNMR andgel permeation chromatography (GPC). Their liquid crystalline properties and the phasetransition temperature were studied by DSC, POM,1D-WAXD and small angle X-rayscattering (SAXS). The results indicated that these polymers had a bilayer smetic C phase,because their interlayer spacings were all about9nm, which was much longer than theirmolecular length. The photoresponsivity of polymers were also confirmed by UV-Visabsorption. All the polymers had a similar Uv-Vis absorption spectrum and photpresponsitywith monomers. However the peaks of their UV-Vis absorptions were red shifted and had alonger response time.Thirdly, we sythenized a bent-core liquid crystalline polymers wiht polysiloxane as itsmain chain basd on our liquid crystalline monomer MB1and a liquid crystalline elastomerwhose main chain were also polysiloxane based on the monomer MB1and MB2. Thestructure and molecular weight of the PMB1was characterized by1HNMR and GPC. Itsliquid crystalline property and the phase transition temperature were studied by DSC, POM,1D-WAXD and SAXS. The results indicated that the polymer had SmA phase, different fromthe PMA series. Its interlayer spacing was5.1nm. The photoresponsivity of the polymer wasconfirmed by UV-Vis absorption. It had a similar Uv-Vis absorption spectrum andphotoresponsity with its monomer. What’s more, the peaks of its UV-Vis absorptions were also red shifted and had a longer response time. Furthermore, the UV light-induceddeformation of the elastomer was studied by exposing it to an intense beam of UV radiation.