Thermotropically mesomorphic polymers

CYCLOLINEAR POLYORGANOSILOXANES A NEW CLASS OF THERMOTROPIC MESOMORPHIC POLYMERS... 

Note 2 A polymer composed of molecules that have rigid rod-like groups or chains usually does not show thermotropic mesomorphic behaviour because decomposition occurs below its melting point. 

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. 

It has been experimentally found by using a whole complex of physical methods that some polymers can exhibit lyotropic and thermotropic mesomorphism. 

Another class of mesomorphic polymers widely studied at present are comb-like polymers containing mesogenic groups in the side groups leading to thermotropic mesomor-phism. 

Hence, the analysis of conformational properties of an extensive class of comb-like polymers with mesogenic side groups showed that the appearance of thermotropic mesomorphic structures in the melts of these polymers is determined by the spontaneous formation of liquid crystalline fragments on a molecular level as a result of the interaction between the side groups. 

Shibaev, V.P., Freidzon, S., Kostromin, S.G. Molecular architecture and structure of thermotropic liquid crystal polymers with mesogenic side chain groups. In Shibaev, V.P., Lam, L. (eds.) Liquid Crystalline and Mesomorphic Polymers, pp. 77-120. Springer-Verlag, New York (1993)... 

Since 1975 when the first thermotropic liquid-crystalline polymer was synthesized by Roviello and Sirigu (13), many mesomorphic polymers were prepared by both academic and industrial reserchers. 

Polymer/surfactant complexes may exhibit thermotropic mesomorphism as well as the lyotropic one discussed above. Among conducting polymers, PANi has been of considerable scientific interest because of its unique electrical and optical properties and environmental stability. Besides the covalent alkyl substitution di.scussed above, a significant approach has been to use functionalized acids, which usually serve as surfactants. Dodedcylbenzenesulfonic acid (DBSA) has been widely used for protonation of PANi and found to improve the solubility and processibility of the conducting polymer. 

Thermotropic mesomorphism in linear polymers had been considered theoretically prior to 1975 (see reference 3 for leading references). However, in 1975, de Gennes explicitly considered linear polymers having alternating rigid mesogenic groups and flexible spacers in the polymeric main chain. He predicted possible nematic behavior for such polymers. 

The mesomorphic state may be realized in two ways, namely, the two ways in which ordinary fluid phases are formed from solids dissolution and fusion. These two categories of mesomorphism are called lyotropism (liquid-crystalline solutions) and thermotropism (liquid-crystalline melts), respectively. The latter category consists of single-component substances and encompasses the large variety of low molecular weight mesogens used in LCDs. More recently, thermotropic specialty polymers... 

A specific property of liquid crystals is the ability to undergo structural transformadons under the effect of electric and magnetic fields. The appearance of lyo- and thermotropic mesomorphism in polymer systems also implies the possibility of controlling their structural-optical properties with external fields. This ability to alter the structure in electric and magnetic fields was one of the most convincing arguments in support of the validity of existence of polymers in the LC phase in general. 

I. Cholesteric pitch and pol5Tner concentration. Macroinolecules 17(8) 1512-1520 Wojciechowsld P (2000) Thermotropic mesomorphism of selected (2-hydroxypropyl)cellulose derivatives. J Appl Polym Sci 76(6) 837-844... 

This paper is primarily concerned with polymers displaying thermotropic mesomorphism. The moieties which generate the liquid crystalline organization are called the mesogenic moieties and can be found either in the main chain or in the side groups. The structural characteristics associated with liquid crystalline behavior have been reviewed by Gray (6, 7) and will not be dis-... 

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl-1,4-phenylene oxide) (PPO) containing pendant mesogenic units separated form the main chain through spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium co -(4-oxybiphenyl) alkanoates and potassium u-(4-methoxy-4-oxybiphenyl)-alk.an oates. While PPO required ten methylene units as a spacer and 4,4 -methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism,... 

The contemporary period is characterized by a rapid accumulation of information about thermotropic polymeric liquid crystals. It is yet too diversified and, as a rule, gives only a qualitative description of the observed phenomena. The next step in LC polymer investigations should be aimed at a quantitative description of their behaviour. This approach should necessarily lead to progress in the comprehension of the quite peculiar mesomorphic state of matter as well as in the introduction of LC polymers into technological practice. 

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