THE ROLE OF THE SPACER IN DISCOTIC POLYMERS
THE ROLE OF THE SPACER IN DISCOTIC POLYMERS
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DOI：
10.1002/marc.1993.030140602
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发表时间：
1993-06
期刊：
影响因子：
--
通讯作者：
M. Werth;H. Spiess
中科院分区：
文献类型：
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作者：
M. Werth;H. Spiess
液晶聚合物（LCP）的开发引发了聚合物和液晶领域的大量研究活动。 LCP 的兴趣在于液晶新材料特性及其在设备中应用的可能性。特别是剪切诱导的取向和更高的材料强度是有希望的新性能以及抑制结晶和在玻璃态下保留特定取向模式的可能性。另一方面，事实证明，基于聚合物链各向异性有序概念，LCP 在开发新型高模量聚合物纤维方面取得了丰硕成果。在具有棒状介晶的侧基LCP的设计中，间隔基~概念~.~)长期以来一直是无可争议的指导方针。柔性间隔基被认为是实现聚合物链形成无规卷曲的趋势和介晶以各向异性堆积方式排列自身的趋势之间良好解耦所必需的。人们期望更长、更灵活的间隔物，并证明其解耦作用更有效，并且有利于更高度有序的相。盘状液晶最近引起人们的兴趣主要是因为它们形成柱状中间相的倾向。柱状排列在新型有机超导材料或具有不寻常磁性行为的有机材料中发挥着关键作用5)。因此，几年前合成了盘状主链和侧基聚合物，希望获得与棒状聚合物类似的优点和新性能6-*)。在他们的设计中，使用了同样适用于棒状聚合物的原理。然而，主要由于它们的综合性较差，尚未进行系统研究来检验这一猜想。本文的目的是提出此类系统研究，其中盘状侧基聚合物在以下方面有所不同：i) 聚合物主链的柔性 (1-3)，ii) 介晶侧链的长度和支化 (3-5)，iii) 间隔基与盘的连接，即酯或醚键 (3, 6, 7 与 8-10)，以及 iv) 脂肪族间隔基的长度 (3, 6、7 和 8-10)。选择六取代苯并菲作为盘状核，因为它经常用于低摩尔质量盘状液晶，并且因为大多数先前的盘状聚合物都是该核。在这些研究过程中，结果表明经典间隔原理及其上述含义对于盘状聚合物无效。讨论中给出了基于含有柱状结构的聚合物的新概念的结果和可能的论据。为了更好地建立这个概念，还研究了一系列同系的杂取代低摩尔质量液晶。
The development of liquid crystalline polymers (LCPs) has initiated substantial research activities in the field of polymers as well as that of liquid crystals'). The interest in LCP lies in the possibilities of new material properties of liquid crystals and their application in devices. Especially shear-induced orientation and higher material strengths were promising new properties as well as the possibility to suppress crystallization and to preserve specific orientation patterns in the glassy state. On the other hand LCPs proved to be fruitful in developing new high-modulus polymeric fibers based on the concept of anisotropic ordering of the polymer chains'). In the design of side group LCPs with calamitic mesogens the spacer~ oncept~.~) for a long time has been the unchallenged guideline. A flexible spacer was considered necessary to achieve a good decoupling between the tendency of the polymer chain to form a random coil and the tendency of the mesogens to arrange themselves in an anisotropic packing. Longer and more flexible spacers were expected and proved to be more effective in their decoupling action and to favour more highly ordered phases. Discotic liquid crystals recently received interest mostly from their tendency to form columnar mesophases. Columnar arrangements play a key role in the novel organic su-perconducting materials or in organic materials having unusual magnetic behaviour 5). Thus discotic main chain and side group polymers were synthesized a number of years ago in the hope of achieving similar advantages and new properties as for calamitic polymers6-*). In their design the same principles were used which work so well for calamitic polymers. However, mainly due to their awkward synthesis no systematic studies have been undertaken to test this conjecture. It is the purpose of this paper to present such systematic studies where discotic side group polymers were varied in: i) the flexibility of the polymer main chain (1-3), ii) the length and the branching of the side chains of the mesogens (3-5), iii) the link of the spacer to the discs, ie ester or ether linkage (3, 6, 7 vs. 8-10), and iv) the length of the aliphatic spacer (3, 6, 7 and 8-10). Hexasubstituted triphenylene was chosen as the discotic core since it is frequently used in low-molar-mass discotic liquid crystals and since most previous discotic polymers are of that core. During the course of these studies it turned out that the classical spacer principle with its implications given above is not valid for discotic polymers. The results and possible arguments based on a new concept for polymers containing columnar structures are given in the discussion. In order to better establish this concept a homologous series of heterosubstituted low-molar-mass liquid crystals is also