【作者】 朱生勃；

【导师】 刘骞峰；

【作者基本信息】 西安建筑科技大学 ， 应用化学， 2009， 硕士

【摘要】 本论文研究了乙撑基桥键类含氟液晶的合成方法,探讨了液晶性能与分子结构之间的关系。同时,作者设计了具有不同结构的乙撑基桥键类含氟液晶单体,并以中间体4-[2’-(反式-4"-正丙基环己基)乙基]环己酮为基本原料合成了三个性能优良的液晶单体。通过测定其物理性能参数来研究和探讨官能团对液晶性能的影响。本论文由以下四部分组成:第一部分,探讨了液晶性能与分子结构之间的关系。包括液晶的物化稳定性与分子结构之间的关系、相变温度与分子结构之间的关系、粘度与分子结构之间的关系、介电各向异性与分子结构之间的关系以及双折射率与分子结构之间的关系。第二部分,以反式-4-正丙基环己基甲酸和4-羰基环己基甲酸乙酯为原料,通过羧酸还原、溴代反应、羰基保护、酯还原、格氏反应、水解、醇脱水、加氢8步反应合成了中间体4-[2’-(反式-4"-正丙基环己基)乙基]环己酮。并用气相-质谱联用仪(GC-MS),红外光谱(IR),核磁共振氢谱(~1HNMR)确认了结构。第三部分,4-[2’-(反式-4"-正丙基环己基)乙基]环己酮可与带有不同取代基的溴苯通过格氏偶联反应、脱水反应、加氢反应合成液晶单体。本文共合成三个液晶单体:1-乙氧基-2,3-二氟-4-(反式-4-(2-(反式-4-正丙基环己基)乙基环己基)苯、3,4,5-三氟-4-(反式-4-(2-(反式-4-正丙基环己基)乙基环己基)苯、3,4-二氟-4-(反式-4-(2-(反式-4-正丙基环己基)乙基环己基)苯。并采用气相色谱分析了产品的纯度,气相-质谱联用仪(GC-MS)和红外光谱(IR)确认了目标化合物的结构。第四部分,测试了三个目标化合物的液晶性能,并与其它七个结构相似的液晶单体做了性能比较,得到如下结论:(1)乙撑基对液晶性能的影响对于介电各向异性为负的分子,乙撑基的引入降低了其负介电各向异性;对于介电各向异性为正的分子,乙撑基的引入降低了其正介电各向异性,使液晶分子极性变弱。乙撑基与清亮点的关系受分子结构和乙撑基所在位置的影响。乙撑基的引入降低了液晶分子的双折射率,拉长了分子的长轴,增大了粘度,使响应速度变慢。(2)氟原子对液晶性能的影响对于骨架相同,且介电各向异性为正的分子,氟原子取代基的多少对液晶分子的清亮点、双折射率和介电各向异性均有影响。氟原子取代基越多,清亮点越低,介电各项异性越小,双折射率越大。总之,本论文给乙撑基含氟类液晶的合成有一定的借鉴作用,对研究官能团对液晶性能的影响有重要的意义,为设计性能更加优良的液晶分子有重要的参考价值。更多还原

【Abstract】 Synthesis of liquid crystals containing ethylene bridge and fluorines was studied. The relationship between liquid crystal properties and molecular structure was discussed.At the same time,the author designed liquid crystal compounds containing ethylene bridge and fluorines with different structure.Three liquid crystal compounds which have excellent properties had been synthesized by the intermediate 4-(2-(4-propylcyclohexyl)ethyl)cyclohexanone.The effects of functional groups on liquid crystal properties were studied and discussed through analyzing their physical performance parameters.This thesis consists of four parts:Part one,the relationship between liquid crystal properties and molecular structure was discussed.It includes the relationship between the physical and chemical stability, the phase transition temperature,the dielectric anisotropy,the birefringence and the liquid crystal molecular structure.Part two,the compound 4-(2-(4-tans-propylcyclohexyl)ethyl)cyclohexanone was synthesized from trans-4-propylcyclohexanecarboxylic acid and ethyl 4-oxocyclohexanecarboxylate via eight step reactions,namely carboxylic acid reduction,substitution of hydroxyl by bromine,carbonyl protection,ester reduction, Grignard reaction,hydrolysis,dehydration reaction,catalytic hydrogenation.This compound was identified by GC-MS,IR and ~1H NMR.Part three,4-(2-(4-tans-propylcyclohexyl)ethyl)cyclohexanone can be used to synthesize many liquid crystal monomers via Grignard reaction,dehydration reaction, catalytic hydrogenation.Three liquid crystal monomers have been synthesized: 1-ethoxy-2,3-difluoro-4-(4-(2-(4-propylcyclohexyl)ethyl)cyclohexyl)benzene, 1,2,3-trifluoro-5-(4-(2-(4-propylcyclohexyl)ethyl)cyclohexyl)benzene, 1,2-difluoro-4-(4-(2-(4-propylcyclohexyl)ethyl)cyclohexyl)benzene.The purity of all of the productes were analyzed by gas chromatography.The target compounds were identified by GC-MS and IR.Part four,testing the performance of the liquid crystal compounds and comparing with seven similar liquid crystal monomers get the following conclusions:(1) Effects of ethylene on liquid crystal performanceFor a negative dielectric anisotropy liquid crystal molecule,the introduction of ethylene into the molecular structure reduce its negative dielectric anisotropy.For a positive dielectric anisotropy of the molecule,the introduction of ethylene into the molecular structure reduce its positive dielectric anisotropy,so weaken the polarity of the molecular structure.Molecular structure and the location of ethylene impact the relationship between ethylene and clearing point.The introduction of ethylene reduces the birefringence of liquid crystal molecule.The introduction of ethylene lengthens the long axis of the molecule,increases the viscosity,slows the response speed.(2) Effects of fluorine on liquid crystal performanceFor positive dielectric anisotropy liquid crystal molecules with the same carbonic skeleton,the number of fluorine atoms impact clearing point,birefringence and dielectric anisotropy.The more fluorine atoms,the lower clearing point,the smaller dielectric anisotropy,the greater birefringence.In short,this thesis is useful for the synthesis of liquid crystals containing ethylene bridge,and is of great significance to study the relationship between fluorines and liquid crystal properties,and is of value for designning a more excellent liquid crystal molecule.更多还原