侧基甲壳效应和甲壳型液晶高分子

侧链液晶高分子体系里,液晶基元可以通过尾接或腰接的方式与主链相连.一般认为,在液晶基元与主链间插入一段长度合适的＂柔性间隔基＂可有效实现主、侧链间的动力学去偶合,从而有利于侧基液晶基元之间的有序排列.作为一类特殊的腰接型侧链液晶高分子,甲壳型液晶高分子中体积较大的侧基（如棒状液晶基元）通过非常短的间隔基或仅通过一个碳-碳键直接横挂至主链上,这导致了强烈的甲壳效应,使得主链被迫伸展.因此,可从与＂柔性间隔基＂完全不同的角度出发,充分利用主链和侧基间的偶合作用,设计甲壳型液晶高分子.本文综述了腰接型侧链液晶高分子中的侧基甲壳效应、甲壳型液晶高分子中由主链与侧基相互作用所导致的特殊构象以及液晶相结构.研究表明,侧基甲壳效应在调控甲壳型液晶高分子的形状、尺寸以及螺旋结构等方面有重要作用.甲壳型液晶高分子可作为刚-柔嵌段共聚物的刚性链段,也可作为主/侧链结合型液晶高分子的主链部分参与到多层次分级超分子有序结构的构筑之中.

Side-chain jacketing effect and mesogen-jacketed liquid crystalline polymers

Side-chain liquid crystalline polymers （LCPs） with the mesogens either terminally or laterally attached to the backbone are usually synthesized based on the concept of ＂flexible spacer＂. The insertion of spacers with reasonable lengths between the backbone and mesogens can effectively decouple dynamics of backbone and mesogen, and thus facilitate ordered packing of side-chains. In contrast to that, the molecular design of mesogen-jacketed liquid crystalline polymers （MJLCPs）, which belong to the catalog of laterally attached side-chain LCP, attempts to take the advantage of the coupling of side-chain and backbone. At the chemical structure level, the feature MJLCP is that the relatively bulky side-groups such as calamitic mesogens are linked to the backbone through a very short linkage or even a single carbon-carbon band. This arrangement of side-chains can cause significant ＂jacketing＂ effect, forcing the backbone to well extend. In this review, we discuss the ＂jacketing＂ effect, the special chain conformations of MJLCP due to the ＂jacketing＂ effect, and also the liquid crystalline phase structures of MJLCP. We demonstrate that the shape and dimension of MJLCP can be tuned upon using the ＂jacketing＂ effect. Furthermore, MJLCP can be used as rod-like component in block copolymers and also as main-chain part in combined main-chain/side-chain LCPs, which can render interesting hierarchical supramolecular orderings.