Pendant mesogen structure

Note 4 The pendant groups in these polymers have structures compatible with liquid-crystal formation, that is, they are mesogenic but not intrinsically mesomorphic. See the examples given in Definitions 2.10 2.11.2.1. 

Another nice piece of work was provided by Chen et al. [325,326] on structurally related branched systems. In this work cyano-containing mesogenic pendants were grafted onto various polyvalent central cores. 

In contrast to these lyotropic mesogenic materials, which require the presence of a solvent in order to produce a mesophase, thermotropic mesogens are those compounds which exhibit a mesophase in the melt state at temperatures above the crystalline solid state and before the formation of an isotropic melt Mesophase-forming polymers may possess either one of the two basic structures shown in Fig. 1 the polymer may either contain the mesogenic group (the part of the polymer molecule which is responsible for liquid crystallinity) directly in the main chain, or the mesogen may be present as a pendant group in the side chain. 

An interesting new development uses liquid crystal polymers (LCPs) to produce materials with exceptional physical and mechanical properties. Generally the LCP resin comprises of a polymer chain with structural units (mesogenic groups) which can be incorporated into the polymer backbone, or incorporated as a pendant group, or both. One approach is to use the epoxy resin system [18] ... 

Percec and coworkers [184] utilized a similar strategy for the conversion of perfluorinated alkylene functionalized 3,4,5-trihydroxy benzoic acid-type dendrons into methyl methacrylate functionalized dendritic macromonomers. Characterization of the resulting linear-dendritic architectural copolymers involved DSC, x-ray diffraction, and thermal optical polarized microscopy. It was concluded that the self-assembly of the pendant dendritic mesogens forced the linear backbone into a tilted, helical ribbon-type structure. The self-assembly behavior was largely controlled by the multiplicity, composition, and molecular weights of the pendant dendritic mesogens. 

These are divided into two broad classes main-chain LCPs and side-chain LCPs. Because in the latter the mesogenic side-chains are usually rather short and of uniform length, we prefer to name the side-chain LCPs as pendant LCPs. Both main-chain and pendant LCP families have been extensively described in the literature [59,60, 92 - 96] so that they need not be described below in great detail. However, examples will be given of main-chain and pendant LCPs demonstrating various structural features and chemical families, in order for the reader to appreciate the variety of such LCPs and the synthetic ingenuity invested in their creation. 

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