Mesomorphic influence

These differences on the stress-strain behavior of P7MB and PDTMB show the marked influence of the mesomorphic state on the mechanical properties of a polymer. When increasing the drawing temperatures and simultaneously decreasing the strain rate, PDTMB exhibits a behavior nearly elastomeric with relatively low modulus and high draw ratios. On the contrary, P7MB displays the mechanical behavior typical of a semicrystalline polymer. 

There are several very important advantages we obtain from this novel class of LC polymers. They can be prepared with well defined chain ends and narrow molecular weight distribution. Therefore, we could provide important information concerning the influence of the nature of the polymer chain ends on their mesomorphic... 

The melting point of the L mesomorphic phase of alkyl ether nonionic surfactants taken from the results of Mitchell et (1983) showing the influence of alkyl and hydrophilic (EO) chain lengths. 

In order fo furfher invesfigafe fhe influence of fhe sfrucfure of the mesogenic units on the mesomorphic behavior of the dendrimers, bulky units have been introduced at the periphery of the third and fourth generations of amino-terminated PAMAM and PPI (Fig. 39, L3, Le, L9), wifh the aim of achieving cubic mesophases, since the increased volume around the dendritic core could in principle force the dendrimer to adopt a globular conformation [199,222],... 

The majority of the early experiments were carried out on a variety of alkoxy-substituted phthalocyanines on the basis of which the following qualitative conclusions could be drawn (a) the intra-columnar mobility was relatively insensitive to the nature of the peripheral alkyl chain substituents which did however influence the mesomorphic properties (b) the mobility invariably decreased on... 

The results observed for 13 and 14 clearly showed the strong influence of the orientation of the ester linking function on the mesomorphic properties. An explanation of this influence was attempted from stereoelectronic and structural considerations (Scheme 9-1). In A, the organic unit used to prepare 13, electron delocalization occurs from the O-atom of the alkoxy chain to the ester function. Thus, mesomerism takes place in the external part of the organic fragment. However, in B, from which series 14 was built up, electron delocalization appears in the interior of the organic core, and in the opposite direction. Consequently, the O-atom of the ether group is more polar in A than in B. Furthermore, examination of CPK... 

Q = 1.3gcm , lu = 5.2 A and M = 265 (for CA), one obtains = 26 according to Eq. (13), and, from Eq. (11), Vp = 0.284 at incipience of a nematic (or cholesteric) phase. The experimental values in Table 3 are generally somewhat greater than this result, but the differences are not beyond the uncertainty in the characteristic chain dimension, here represented by o/n. Inasmuch as this ratio depends on the solvent, as is well known, dependence of the threshold Vp on the solvent is to be expected. Available data do not permit a definitive correlation, however, between Vp at incipience of the mesomorphic phase and the influence of the solvent on chain flexibility. 

The orientation-dependent, soft interactions here considered doubtless play an important role in polymers and copolymers exhibiting mesomorphic behavior. Such polymers typically contain aromatic residues, having large anisotropies, as integral members of the chain backbone. These interactions are especially prominent in melts and concentrated solutions, as has been pointed out. Their influences in mesogenic polymers have received little attention. 

The study by Percec, Tomazos and Willingham (15) looked at the influence of polymer backbone flexibility on the phase transition temperatures of side chain liquid crystalline polymethacrylate, polyacrylate, polymethylsiloxane and polyphosphazene containing a stilbene side chain. Upon cooling from the isotropic state, golymer IV displays a monotropic nematic mesophase between 106 and 64 C. In this study, the polymers with the more rigid backbones displayed enantiotropic liquid crystalline behavior, whereas the polymers with the flexible backbones, including the siloxane and the polyphosphazene, displayed monotropic nematic mesophases. The examples in this study demonstrated how kinetically controlled side chain crystallization influences the thermodynamically controlled mesomorphic phase through the flexibility of the polymer backbone. 

In this review, we will focus on ion- and electron-conductive thermotropic LC polymers and oligomers. A variety of mesomorphic structures has been constructed utilizing non-covalent interactions, which influences ionic and electronic carrier transport processes. 

Some studies dealing with the solid state properties of graft copolymers with liquid-crystal side chains have appeared in the literature [353-355]. The main attention is focused on the influence of molecular parameters (nature of the backbone and the side chains, molecular weight, etc.) on the mesomorphic properties of the liquid-crystal side chain. Salt complexes of PEO grafted onto various backbones were also considered [356] and the influence of the nature of thebackbone and salts on the conductivity of the resulting materials was studied. 

In summary, there are many good reasons for studying lipid mesomorphism and the dynamics and mechanism of lipid phase transitions. The dynamic measurements enable limiting transition rates to be established and provide a basis for formulating, evaluating and refining transition mechanisms. Such measurements also reveal details of molecular structure and overall composition that influence phase stability and modulate transition rates and mechanism. The ultimate goal is to understand phase behavior and transition mechanism at a fundamental level and, thereby, effect control over lipid phase relations in vivo and in reconstituted, model and formulated systems. 

A detailed understanding of the influence of the structure, charge, and counterion on the thermal and mesomorphic properties requires the preparation and further study of ferrocenium materials. The above-reported results prove that liquid-crystalline switches should, in principle, be available by the incorporation of ferrocene/ferrocenium into mesomorphic materials. 

The data obtained for 58 ( ) and 59 further emphasize the influence of the substitution pattern on mesomorphic properties. Whereas a two-aromatic ring system (plus the Cp nucleus) was found to be non-mesomorphic for 1,3-disubstitution,introduction of an additional substituent on the second Cp ring gave monotropic liquid crystals 58 ( ). This result indicated that the repulsive interactions induced by the Fc core are compensated, at least in part, by the third substituent. This allows both substituted Cp rings to interact favorably, which results in mesomorphism promotion. In a structure such as 59, the depth (bulkiness) of Fc (about 3.3 A) is, in a way, hidden by the substituents anchored on the two Cp nuclei. Therefore, the 1,1 -3-trisubstitution pattern is a stronger mesomorphic promoter than the 1,3-disubstitution one (for identical substituents). This is supported by the fact that 46( =16), the 1,3-disubstituted counterpart of 59, gave a much narrower liquid-crystalline range (42 °C) than 59. 

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