Research On Synthesis And Properties Of Novel Mesogen-Jacketed Liquid Crystal Polymers With Amido Bonds

The mesogen-jacketed liquid crystalline polymers are a new type of liquid crystalline polymers. In such polymers, the rigid mesogenic groups are attached laterally to the backbone through their center of gravity with short or no spacers. Because of the unique molecular architecture, the mesogen-jacketed liquid crystalline polymers have many special properties.In this paper, a new kind of mesogen-jacketed liquid crystalline polymer with mesogens of aromatic amide structure, poly{2,5-bis-[(4-me-thoxyphenyl) aminocarbonyl] styrene} was successfully synthesized. The synthetic route and reaction conditions were optimized in the paper.2-methylterephthalic acid was synthesized by selective oxidation of2,4-dimethylbenzoic acid using KMnO4. The best experimental program was obtained by the orthogonal experimental method, which was the molar ratio of KMnO4, NaOH and2,4-dimethyl-benzoic acid was2.2:1.5:1, the reaction temperature was60℃. Dimethyl2-methylterephthalate was synthesized by methanol and acyl chloride, which was obtained from the reaction of SOCl2and2-methylterephthalic acid. Meanwhile the structure of monomer and PMPACS were characterized by1H-NMR,MS, Elemental Analysis, and the molecular weight of PMPACS were characterized by GPC.In order to control the molecular weight of PMPACS, The effects of reaction temperature,reaction time,concentration of monomer and initiator on polymerization were investigated. The results indicated:(1) the high conversion and the polymer with high molecular weight could be obtained when the reaction temperature was60℃.(2)The conversion increased to80%wt quickly in16h and maintained till the reaction finished. The molecular weight of PMPACS also increased as the reaction time increased.(3)The relationship among the polymerization reaction rate and the concentration of monomer and AIBN is Rp=kp[M][I]1/2.(4) The conversion increased as the concentration of monomer increased from0.25mol/L to0.5mol/L. However, the molecular weight of PMPACS increased as the concentration of monomer increased till0.375mol/L, afterwards it decreased as the concentration of monomer increased.(5) The molecular weight of PMPACS decreased as the concentration of AIBN increased.Two PMPACS samples with different molecular weight, Mn=3.9×104g/mol and Mn=13×104g/mol, were prepared by controlling reaction conditions. TGA,DSC,POM,XRD and FTIR were used to analyze the thermal properties, liquid crystal behavior and hydrogen bonding interaction of PMPACS. The results showed that PMPACS had good thermal properties with Tg=245×and the initial weight loss temperature384×. From POM tests, it could be found that PMPACS was thermotropic liquid crystal and the liquid crystal behavior could be observed at278×. FTIR tests indicated that there was strong hydrogen bonding interaction between PMPACS molecular and it would be weak when samples were heated. However, it needs to be further studied whether PMPACS is lyotropic liquid crystal or not.