Polymerizable mesogen

Peglow et al. (4) prepared polymerizable mesogenic materials consisting of a dichromophoric dichroic network containing azo-chromophores, which were used for preparing dichroic polymer networks and gels. 

With a different ferroelectric LC-polymer it was even possible to obtain very homogenous FS-films of thicknesses of only 6 to 16 layers as determined by both optical and X-ray reflectometry (5polymeric films contained a small fraction of polymerizable mesogenic side-groups, it was even possible to photocrosslink these systems. It should be mentioned that in this first case the crosslinking caused some changes in film morphology, but the resulting films are very stable and do not even break when small holes are formed by mechanical stress (JS),... 

Greenfield et al., obtained a patent on polymerizable mesogenic or liquid crystalline compounds with cinnamic acid residue and aUcyne groups. 

Regarding the chemical constitution of these monomers, the polymerizable, functional group was always directly linked to the rigid, voluminous mesogenic moieties. As space filling models indicate, polymers result, having a rigid main chain. This... 

Multireactive mesogenic triester derivatives, (I), containing at least two polymerizable components were prepared by Farrand [1] and used as synthetic resins with anisotropic mechanical properties. 

Due to the limitations of non crossiinkable cyclic liquid crystalline siloxanes resulting from the fact that the Tg is dominated by the mesogenic groups connected to the cyclic siloxane backbone and, therefore, other aspects for the selection of the mesogens are limited, a crossiinkable system had to be established. This strategy requires the presence of polymerizable moieties within the side chain groups, such as epoxide, einnamate or (meth)acrylate groups. Methacrylates are preferred due to their reasonably fast photopolymerization and thermal stability. 

As for low molecular weight surfactants, the superstructures are assumed to be formed by micellar aggregates [126], But it seems that the formation of lyotropic liquid crystals is supported by the additional presence of thermotropic mesogens [87,122-124,126], Lamellar, hexagonal, cubic and even nematic and cholesteric mesophases were reported for binary systems, the latter being exceptional. Lyotropic mesophases were also observed in non-aqueous solvents [240,400,401,405], If polymerizable surfactants are studied, not only the phase diagram but also the types of mesophases observed for the monomer and the polymer may be different. 

Macromonomeres, styrenic, of polyoxyethylene 52 Maleic derivatives 49 Mechanical stability 47 Mesogens, disc-like 216 Methacrylates, activated 3 -, -, reactivity ratios 7 Methacrylic polymerizable end groups 52 Methyl free radicals 88 Micelle concentration, critical 47, 48, 55 Mono-radicals 91-103... 

Homopolymers. Phenylesters of benzoic acid were chosen as mesogenic groups for the synthesis of suitable monomers. The acryloyl- and the methacryloyl moieties were used as polymerizable groups. The flexible spacer was an alkyl chain or an alkyloxy chain of varying length. Thus a homologous series of p-"(2-methylpropenoyloxyalkyoxy) benzoic acid -p substituted phenyl esters 1 was prepared. The monomers were synthesized by the standard methods as follows ... 

They are well-defined building units for hybrid materials [50-52]. Those with mesogenic R groups can exhibit liquid crystal properties [53, 54], and those with polymerizable R groups (acrylate, epoxide, vinylic) can be copolymerized with organic polymer precursors. As a last example of the wide interest in this compounds, those with an incompletely condensed structure (open cage) or incorporating other metals can be models for zeolites and are used themselves as catalysts [55-57]. 

Sentman, A. C. Gin, D. L. Polymerizable bent-core mesogens switchable precursors to ordered, polar polymer materials. Angew. Chem. Int. Ed. 2003, 42, 1815-1819. 

There are two main approaches to the synthesis of side-chain FLCPs. The first one consists of the synthesis of low-molar-mass mesogenic molecules having a polymerizable group at the molecular end, with further polymerization (Fig. 6a). (It should be noted that the monomers themselves are often, although not necessarily, ferroelectric liquid crystals.) In that way, many dozens of ferroelectric LC polyacrylates and polymethacrylates have been synthesized. 

Liquid crystalline siloxanes are limited with respect to the glass transition in comparison to other backbone systems, such as poly(meth)acrylates. Class transition temperatures of up to 80 °C can be achieved, but there is a limit for the variations of the mesogenic groups l Therefore, cross-linking is the preferred method. The presence of at least some polymerizable moieties within the side chain groups is necessary. Typical examples for these groups are epoxides, cinnamates, or methacrylates. 

Using itaconic acid esters as the unsaturated polymerizable compounds [22], it is possible to obtain polymers containing a pair of mesogenic fragments in each monomeric unit (cf. Fig. 6.3b) ... 

One of the first reports on the orientation and subsequent crosslinking of a reactive mesogen for OLED applications with polarised emission has been published by Bacher et al. [63], who synthesized the conjugated bis-stilbene with two polymerizable acrylate groups shown in Fig. 7.17. The reactive mesogen was oriented by heating into the liquid crystalline phase and subsequently thermally crosslinked at 175°C. 

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