通过硝基热还原法、Williamson醚合成法、Steglich酯化反应合成了3种偶氮苯液晶基元单体(LC),在氮气气氛下通过与1,6-己二异氰酸酯(HDI)反应,并以甲醇封端制备出3种主链型偶氮苯液晶聚氨酯(LCPU),采用核磁共振氢谱仪(1H-NMR)、傅里叶变换红外光谱仪(FT-IR)、热重分析仪(TG)、差示扫描量热仪(DSC)、热台显微镜(POM)、紫外-可见分光光度计(UV-Vis)对LC及LCPU进行了表征。1H-NMR、FT-IR对LC及LCPU分子结构的表征结果符合预期;TG、DSC、POM分析结果表明LCPU热稳定性良好,LC和LCPU具有良好的液晶性。与4,4′-二氧己醇偶氮苯(记作LC1)和4,4′-二对氧己醇苯甲酸酯偶氮苯(记作LC3)相比,具有不对称结构的4-氧己醇-4′-对氧己醇苯甲酸酯偶氮苯(记作LC2)具有更高的玻璃化转变温度,偶氮苯液晶聚氨酯LCPU2具有较低的玻璃化转变温度和相对较宽的液晶相区间。UV-Vis分析结果表明LC及LCPU在波长365nm紫外光照射下出现了典型的顺反异构转化,具有良好的光响应性。
Three kinds of azobenzene liquid crystal monomers (LC) were synthesized by nitrothermal reduction,Williamson ether synthesis and Steglich esterification.Three main-chain azobenzene liquid crystal polyurethanes (LCPU) were prepared by reacting with 1,6-hexyl diisocyanate (HDI) under nitrogen atmosphere and end-capped with methanol.The LC and LCPU were characterized by nuclear magnetic resonance hydrogen spectrometer (1H-NMR),Fourier transform infrared spectrometer (FT-IR),thermogravimetric analyzer (TG),differential scanning calorimeter (DSC),hot table microscope (POM) and UV-Vis.The molecular structures of LC and LCPU were characterized by 1H-NMR and FT-IR.The results of TG,DSC and POM analysis showed that LCPU had good thermal stability,and LC and LCPU had good liquid crystalline properties.Compared with 4,4′-dioxahexanol azobenzene (labeled as LC1) and 4,4′-dioxahexanol benzoate azobenzene (labeled as LC3),4-oxahexanol,4′-dioxahexanol benzoate azobenzene (labeled as LC2) with asymmetric structure had higher glass transition temperature.Azobenzene liquid crystal polyurethane LCPU2 had a lower glass transition temperature and a relatively wide liquid crystal phase interval.The results of UV-Vis analysis indicated that LC and LCPU exhibited typical cis-trans isomerization under the irradiation of 365nm ultraviolet light,demonstrating good photoresponsiveness.
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