Mesogenic monomers

Similar behavior has also been observed for polymerizations of small amounts of various monomers in ordered LC phases (30). The rate of polymerization is enhanced considerably for a non-mesogenic diacrylate in the smectic C phase and is more than three times that observed in the isotropic phase of the same LC and over six times that observed for polymerization in an isotropic solvent. Similar results were observed for a variety of mesogenic and other non-mesogenic monomers (31). Interestingly, the mechanisms behind this rate enhancement is not the same for all monomers and is highly dependent on the segregation behavior. 

Phase Behavior and Electro-optic Properties. With the great potential of PSFLCs, it is important to understand the changes induced by the polymer network on the FLC properties. In order to do so, two different non-mesogenic monomers, HDDA and PPDA, have been used. The structure of these monomers is quite similar (See Figure 1) with the only difference being that the phenyl group in PPDA is replaced with a six carbon alkyl chain for HDDA. These monomers, despite their structural similarity, have much different physical properties and consequently the polymers formed from HDDA and PPDA may also influence the FLC phase and electro-optic behavior differently. 

Research Focus Synthesis of liquid crystalline interpenetrating polymer networks using photocrosslinkable mesogenic monomers. 

A third mesogenic monomer, (III), was also used to prepare liquid crystalline polymer networks and is illustrated below. 

Entry Mesogenic Monomers Used Monomer Ratios Quantum Efficiency (%) Open Voltage (V) Power Conversion (%)... 

Liquid crystalline polymer networks were prepared by Kelly et al. (1) with mesogenic monomers, (IV), and used in forming networks charge-transporting or luminescent materials. 

Besides, it is possible by copolymerization of one and the same mesogenic monomer with non-mesogenic comonomers to vary the type and temperature range of the mesophase 36,37) (Table 2). It is seen from the table that using alkylacrylates with alkyl groups of different length (A-n) as comonomers and varying the ratio of components it is possible to shift the transition temperatures of a LC phase. 

Copolymerization of two mesogenic monomers is, at the present time, the only pathway to obtain polymers with cholesteric mesophase (see Part 4.4). On the other hand, only by copolymerizing smectogenic and nematogenic monomers and investigating the properties of copolymers in a broad interval of compositions, is it possible to establish the principles of formation of each type of mesophase. We demonstrate... 

Percec et al.130bl have employed 1 — 2 C-branching and ether-type connectivity for the preparation of nonspherical, thermotropic liquid crystalline dendrimers. Observed thermotropic behaviors are predicated on mesogenic monomers that are capable of conformational isomerism. 

Scheme 6.13. Percec et al. s153 application of mesogenic monomers for the preparation of hyperbranched polymers that form isotropic and nematic phases based on monomeric gauche and anti conformations.

The most simple molecular topology of such systems reported so far is a tetrahedral supermolecule obtained by reacting tetrakis(dimethylsiloxy)-silane with alkenyloxy-cyanobiphenyls (Fig. 22), as discussed previously. Such tetramers exhibit smectic A liquid crystal phases [179]. For such end-on materials, microsegregation at the molecular level favors the formation of the smectic A phases in preference to the nematic phase exhibited by the mesogenic monomers themselves. The use of different polyhedral silox-ane systems (Fig. 24) or the Ceo polyhedron as the template for multi- and polypedal hexakis(methano)fullerenes (Fig. 70) substituted with a large number of terminally attached mesogenic groups confirm the same tendency to the formation of smectic A phases (vide supra). 

It is also known that in side-chain LC polymers the copolymerization of optically active monomers with mesogenic monomers, in the same manner as the mixing of optically active compounds with nematic low molecular weight compounds, can induce the formation of a cholesteric mesophase. Therefore, it is expected that inclusion of chiral spacers in main chain liquid crystal polymers, which would be nematic... 

Copolymerize mesogenic monomers to form random copolymers with lower melting temperatures. 

The synthesis of acrylate materials is relatively straight forward, and can be performed without the recourse to complex reagents and equipment, but, because of the polymerization step may require particular care to ensure the purity of the final material. This is particularly so in the following example, where a cyanobenzoate ester is used to provide the anisotropic phase structure, since the electron-withdrawing group makes this ester particularly susceptible to hydrolysis. The first step in the production of a mesogenic monomer involves the acetylation of 6-chlorohexanol using a standard preparative procedure,followed by etherification and subsequent hydrolysis as shown in Scheme 1. 

The same authors prepared a series of liquid-crystalline polysiloxanes copolymerizing the nonionic mesogenic monomer cholest-5-en-3-ol(3P)-10-undecenoate 47 and the ionic mesogenic monomer potassium 2-allyloxy-5-cholesteryloxycar-bonyl-benzenesulfonate 48. 

Polymerization of mesogenic monomers is very effective for obtaining more stable ordered thin films. Triphenylene monomer containing acrylate moiety 18 was photopolymerized by UV light irradiation (Fig. 17). UV light was shone onto the mixture of the triphenylene derivative and a photoinitiator under inert atmosphere. Carrier transport characteristics of the ob-... 

Examples of vinyl monomers for addition polymerization include acrylates, methacrylates, vinyl ethers and styrene derivatives. Radical, ionic, and group-transfer polymerizations are possible according to polymerizabil-ity of the monomers. Living polymerization is difficult because mesogenic monomers often contain bonds such as benzoate ester, which are easily attacked by growing ends. Cyclic and condensation monomers are less... 

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