Compositions – Liquid crystal compositions
Patent
1999-09-13
2000-12-26
Kelly, C. H.
Compositions
Liquid crystal compositions
25229967, 528192, C09K 1952, C09K 1920, C08G 6302
Patent
active
061653829
DESCRIPTION:
BRIEF SUMMARY
FIELD OF APPLICATION
The present invention fits within a first chemical sector with optical implications (response sensitive to temperature: thermal indicators and radiation sensors), as well as biological ones due to their liquid crystal nature (W. Elser and R. D. Ennulat, "Advances in Liquid Crystals", Vol. 2, Brown, G. H. (De.), Academic Press, New York, 1976, pp. 73).
Liquid crystals are self-organizable systems. They do not pass directly from the crystalline state to the isotropic melt, when being heated, but rather they form mesophases that combine the order of the perfect crystal with the mobility of the liquid. Their molecular base is almost always simple: they form anisotropic or amphiphilic molecules with a rigid geometry (mesogenic unity) connected to another flexible part (spacer), that package in blocks with anisotropic properties (H. Ringsdorf, B. Schlarb and J. Venzmer, "Molecular Architecture and Function of Polymeric Oriented Systems: Models for the Study of Organization, Surface Recognition, and Dynamics of Biomembranes", Ang. Chem. Int. De. Engl. 1988, 27, pp. 116). the parallel orientation of their longitudinal molecular axis is common to all mesophases. Two main types may be distinguished: Nematic (with their molecular centers distributed isotropically) and smectic (molecular centers distributed isotropically (and smectic (molecular centers organized in planes). The spatial arrangement of nematic planes stacked in a helicoid superstructure, characterized by a preferably chirality, is known as cholesteric mesophase. Cholesteric mesophases reflect incident light and when their helix pitch is comparable to the wavelength of the visible light, they exhibit typical bright colors.
The development of polymer liquid crystals followed that of monomer liquid crystals and began with polymers whose main chain, as a whole, acted as a mesogene, those prepared from a solution (lyotropic) as well as those prepared from a melt (thermotropic). Subsequently, the mesogenic units were introduced well hung from the main chain by means of a flexible spacer (of side chain) or connected all along the main chain by a flexible aliphatic spacer (of main chain).
In 1982, Lenz et al (C. Ober, J. I. Jin. R. W. Lenz, Polym. J. 1982, 14, 9) synthesized thermotropic polymer liquid crystals whose mesogenic unity, previously studied in works of low molecular weight, based on a central residue of terephthalic acid flanked by two p-oxybenzoil residue connected by flexible polymethylene spacers. High transition temperatures were obtained from transition to the mesophase and to the isotropic melt.
Galli et al. (G. Galli, E. Chiellini, C. K. Obert, R. W. Lenz, Makromol. Chem. 1982, 183, pp. 2693) in 1982 also introduced to the mesogene itself flexible spacers compatible with the aqueous system under physiological conditions, that is to say, hydrophilic spacers with a low molecular weight with hydroxy ending, of the oligo oxyethylene and olio oxypropylene type, the latter containing chiral centers in each unit. These spacers had also been used in low molecular weight liquid crystals, for the purpose of reducing the transition temperatures. The influence of the type, length and distribution of the spacers on the behavior of the formed mesphases was observed, limiting the liquid crystal nature of the polymers to 10 units in the spacer.
In 1983, Malanga et al. (C. Malanga, N. Spassky, R. Menicagly, E. Chiellini, Polymer Bulletin 1983, 9, pp. 336) extended the synthesis, using as flexible spacers optically active dioles with a different length and degree of substitution, capable not only of giving the polymers a hydrophilic nature but also the cholesteric stereochemical arrangement to the mesophase thereof. Starting with chiral glycols (an enantiomer of a specific sign) as the spacer, a polymer with the same optical sign was obtained in all cases. Starting with the racemic mixture of glycol as the spacer, a "racemic" non-chiral polymer with a nematic, never cholesteric, mesophase was always obtained (E. Chiellini, R. Po, S. Carro
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Chiellini et al., Macromolecules, (1990) 23 (8) 2106-12.
Chiellini et al., Polym. Bull., (1983) 9(6-7), 336-43, 1990.
Chiellini et al., 1990, Mol. Cryst. Liq. Cryst. 179:405-18.
Perez Mendez Maria Mercedes
Rocha Carlos Marco
Consejo Superior de Investigaciones Cientificas
Kelly C. H.
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