Monomer mesomorphic

However, the hydrogen-bonded mesogens that are of most interest in the context of this article are those elaborated initially by Kato and Frechet in the early 1990s [24-33]. In this approach, a pyridine, which may or may not have liquid crystal properties, was hydrogen bonded with a 4-substituted benzoic acid to form a new species with its own, distinct mesomorphism. For example, complex 9 shows a SmA phase that persists to 238 °C (n = 2, m = 4), while its free component pyridine is nematic to 213 °C the component benzoic acid is also nematic (as the H-bonded dimer) to 147 °C (although note that the notional monomer would not be liquid crystalline). 

Although numerous amphiphilic monomers have been polymerized and a great number of amphiphilic polymers have been investigated, only some hints in the literature indicate mesomorphic behavior of concentrated polymer solutions 105.106.121>. Nearly all measurements were carried out "at low concentrations, in order to characterize the properties of these polysoaps in view of applications as surfactants. For these applications high polymer concentrations are, of course, not of interest. 

The state of the hydrocarbon chains in mesophases and micelles is reflected in the Krafft phenomena. In aqueous solutions of surfactants the Krafft point is defined as the temperature at which the solubility reaches the critical micelle concentration when the temperature is increased further, the solubility rises rapidly since the monomers form micelles (Figure 5) (10). Lipids that do not form micelles frequently start to swell by the uptake of water at a well-defined temperature they are transformed into a mesomorphous state (Figure 6) (11) The relation between these two Krafft phenomena is explained to some extent by the... 

Studied in ref. [26] is the effect of HFC reaction conditions on the configuration sequences in POCS-4. Since the mesomorphous state in PMCS-4 is formed in stereoregular trans-tactic polymers only [27, 32] and spatial configuration of initial monomers is not always fully preserved in poly-mers, the effect of HFC conditions on transformation of =Si-CI and =Si-OH centers in initial corn-pounds has been studied. The detected fact of cyclosiloxanes partial inversion at Cl atoms substitution at silicon was expected, as reported before [33, 34], More detailed description of reflex correlation was carried out in ref. [35], Symbols and mark projections of units and bonds to the pla-ne perpendicular to the cycle plane. 

The use of hydrogen bonds in liquid crystalUne materials at large is a very active area [63,64]. In the case of main chain thermotropic liquid crystalUne HBSPs, two main approaches have been explored. The first approach is to mix two complementary monomers, usually of the AA -i- BB type (Fig. 1). The complementary hydrogen bonding units utilized are mainly modified nu-cleobases [5,65,66] and aromatic acid/pyridine couples [54,67- 74]. In the most successful cases, the pure components are not mesomorphous, but the mixtures are [65,69-71]. At any rate, the stabiUty range of the mesophase is usually increased. The second approach is to use a self-complementary... 

This is testimony to a partial dissociation of cyclic dimers with the formation of open associates and monomers. In Refs. 57,58, 60 the quantitative estimations of the relative number of different building blocks as functions of temperature and phase of the sample have been made. For reference, the infrared spectra of n-carbonic and perftoralkylbenzoic acids, which do not possess mesomorphic properties, have been studied as well. 

Some special attention should be placed on the p (bulk) phase as well. Although this form is often reported as being non-crystalline, it gives rise to sharp Bragg reflections commensurate with lamellar order with a long period of 12.3 A [74] and fiber periodicity of 16.6 A (which corresponds to two monomer units) [67]. Thus, it differs from real crystals in the sense that it is mesomorphic. This phase also includes the presence of absorbed solvent and may be obtained by extended exposure to solvent vapor or solvent (cf., the solvent section). In particular, it has been found to appear as an intermediate step in the transformation from the solvent induced clathrate-like structure to the solvent-free well-ordered a phase [74], The a and fi (bulk) phases may coexist and are closed related to one another but are still structurally incompatible. 

Not only are there examples of dimers based on mesogens with rod-like structures, there are also examples reported of dimers composed of disclike mesogens, see bottom structure in Fig. 2. Generally for these types of material the pattern of mesomorphic behavior follows that of the analogous monomers. 

Monomers with similar mesogenic moieties have been reported in the literature. In general, these monomers exhibit completely different mesomorphic behavior from previously reported vinyl mesogens, although the only difference is the methacrylate frmctional group. 

Deschenaux, R. Turpin, F. Guillon. D. Ferrocene-containing themiotropic side-chain liquid-crystalline poly-methacrylate from a mesomorphic trisubstituted ferrocene monomer. Macromolecules 4997. 30. 3759-3765. 

Polymers with side chain structure similar to that of low molecular weight liquid crystalline compounds can achieve various levels of organization in the bulk. These polymers are sometimes formed by polymerization of vinyl monomers that themselves exhibit mesomorphic behavior. In other cases, they can be obtained from monomers that do not form liquid crystalline states. At one extreme the structure of the polymer is highly organized, approaching that of crystalline polymers and giving rise to a number of x-ray diffraction peaks. At the other extreme the polymer chains are disorganized, with x-ray diffraction patterns that resemble those from amorphous polymers. 

It is interesting to remark that in both above-mentioned cases, the monomers are not mesomorphic. 

This is a very important finding since it implies that the structure of the polymer is, in this case, independent of the polymerization procedure. Several authors have implicitly granted the possibility to obtain polymers with mesomorphic structure lies in the availability of mesogenic monomers, and on the possibility to polymerize them in the mesomorphic phase. Our results contradict the suggestions. The only difference one can reasonably expect between polymers prepared in the mesomorphic and isotropic phase... 

A New Series of Mesomorphic Monomers Bulk Polymerization of 4-Cyano-4 -biphenyl n + 2)-alkenoates... 

Polymers which exhibit mesomorphic order may have interesting anisotropic properties such as high optical electrical, or mechanical anisotropies. Such polymers may be obtained either by polymerization of a non-mesomorphic monomer in a liquid crystalline solvent (l 2) or by direct polymerization of a mesomorphic monomer in its liquid crystalline state ( 3"9) The organization in the resulting polymers may be improved if the polymerization is done under orienting conditions in electric or magnetic fields or within suitable boundary conditions... 

In this chapter a new series of mesomorphic monomers is presented -- the -cyano- -biphenyl (n+2)-alkenoates. Their bulk polymerization in the nematic state has been investigated, and thin layers obtained by thermal polymerization with or without an orienting electric field have been studied. Dielectric properties are discussed also. 

Figure 6. Apparatus for thermal polymerization of mesomorphic monomers under electric field...

Three mesomorphic monomers belonging to a new series, the -cyano-if -biphenyl (n+2)-alkenoates, were prepared. One of them, the if-cyano- -acrylatebiphenyl, is nematic from 100 to... 

Sadron et al. (l) prepared lyotropic liquid crystalline systems using polymers and a polymerizable solvent and attempted to fix the mesomorphic structure by polymerizing the monomeric solvent. Bouligand et al. (2) attempted to prepare liquid crystalline substances with fixed structure by copolymerizing mono- and bifunctional mesomorphic monomers. However neither group investigated the phase conditions of the monomers or of the monomer and polymer. In both cases identical homogeneous phases were assumed before and after polymerization. 

Figure 3. Polymer/monomer state diagram of p-methyl, p -acryloyloxyazoxybenzene obtained by polarizing microscopy Mp composition (weight fraction of polymer). Characteristic points ( ), decreasing birefringence CY), mesomorphic transition mesomorphic melting (%), solidus (O), liquidus. The meaning of the areas (A), isotropic liquid (B), isotropic liquid -j- mesomorphic plasticized polymer (C), liquid (D), glassy states of plasticized polymer in mesomorphic phase (E), crystalline monomer -f mesomorphic plasticized polymer in the glassy state (F), crystalline monomer -j-mesomorphic plasticized polymer in the liquid state (G), mesomorphic monomer -f mesomorphic plasticized polymer in the liquid state.

Q he greatest changes in enthalpy are observed at Tp, but they are lower than would have been expected (on the basis of molecular dimensions) from crystalline-to-mesomorphic transitions. The cholesteric state was observed at the flow temperature under a polarizing microscope. The cholesteric reflections are observed at lower temperat ares than Tp in systems containing polymers or at Tp of the monomer itself. 

In our present work the mesomorphic state polymerization was investigated from the point of view of solid-state polymerization. The thermodynamic interactions of monomers and polymers can he represented hy state diagrams. Effects reported hy Sadron et al. may only he expected in the homogeneous areas of the state diagrams. The thermodynamic conditions leading to such areas are fulfilled frequently in smectic states hut rarely in cholesteric or nematic ones. 

There exists a mushrooming interest in the mesomorphic behavior of macromolecules in solution. The existence of macroscopic anisotropy requires (at least partial) chain rigidity. This may arise from next nearest neighbor steric restrictions for polymers constructed from bulky backbone monomers as in the polyamides... 

Mesomorphic Order in Block Copolymers from a-Amino Acids and Other Monomers and in Copolymers from a-Amino Acids... 

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