Liquid-crystalline phases of polymers

Finkelmann, H., and Jahns, E. (1989). Association and liquid crystalline phases of polymers in solution. In Polymer Association Structures, El-Nokaly, M. A. (Ed.), ACS Symposium Series 384, pp. 1-20. Am. Chem. Soc., Washington, DC. 

Association and Liquid Crystalline Phases of Polymers in Solution... 

The first part of the book discusses formation and characterization of the microemulsions aspect of polymer association structures in water-in-oil, middle-phase, and oil-in-water systems. Polymerization in microemulsions is covered by a review chapter and a chapter on preparation of polymers. The second part of the book discusses the liquid crystalline phase of polymer association structures. Discussed are meso-phase formation of a polypeptide, cellulose, and its derivatives in various solvents, emphasizing theory, novel systems, characterization, and properties. Applications such as fibers and polymer formation are described. The third part of the book treats polymer association structures other than microemulsions and liquid crystals such as polymer-polymer and polymer-surfactant, microemulsion, or rigid sphere interactions. 

In addition to barotropic liquid crystals of flexible polymers, there are also a few reports on the observation of the liquid crystalline phase of polymers containing no mesogenic units of rigid rods. Aharoni (1988), for example, was very lucky to have found a series of the following polymers that form a thermotropic liquid crystal phase. 

Table IV shows that the values of transition temperatures Tg j slightly decrease with increasing n, which is probably due to the effect of internal plas-tification and was frequently observed in the case of comb-like polymers (21), The evaluation of the thermal effect inherent In this transition for PChMAA-II gave the value of 0,76-0,08 cal/g, which agrees well with the values of heats of melting, corresponding to the liquid crystalline phase-isotropic melt transition for low-molecular liqtdd crystals ( ), However, in contrast to the latter, which, as a rule, crystallize during cooling (see, for example, Pi re 33. the liquid crystalline phase of polymers vitrifies while cooled (Figure 5). In other words, in the case of polymers, the structure of the liquid C3 ystalline phase...

El-Nokaly, M. A. (ed.), Polymer Association Structures Microemulsions and Liquid Crystals , ACS, Washington, DC, 1989. The book discusses formation and characterization of microemulsions and the liquid crystalline phase of polymer association structures. 

As there exists a phase equilibrium both phases must have reached in the internal thermodynamic equilibrium with respect to the arrangement and distribution of the molecules the measuring time. Therefore, no time effects or path dependencies of the thermodynamic properties in the liquid crystalline phase should be expected. To check this point for the l.c. polymer, a cut through the measured V(P) curves at 2000 bar has been made (Fig. 6) and the volume values are inserted at different temperatures in Fig. 7, which represents the measured isobaric volume-temperature curve at 2000 bar 38). It can be seen from Fig. 7 that all specific volumes obtained by the cut through the isotherms in Fig. 6 he on the directly measured isobar. No path dependence can be detected in the l.c. phase. From these observations we can conclude that the volume as well as other properties of the polymers depend only on temperature and pressure. The liquid crystalline phase of the polymer is a homogeneous phase, which is in its internal thermodynamic equilibrium within the normal measuring time. 

In the literature, there are several other coarse-grained polymer models in which spherical monomers are replaced by asymmetric objects. Generally, this gets a host of qualitatively new structures, e.g., liquid crystalline phases of helical secondary structures [99]. In those models, including that... 

M. Marrucci and P. L. Maffettone, Description of the liquid-crystalline phase of rodlike polymers at high shear rates, Macromolecules, 22,4076 (1989). 

Doi, M. Molecular dynamics and rheological properties of concentrated solutions of rodlike polymers in isotropic and liquid crystalline phases. J. Polym. Sci. Polym. Phys. Edn. 1981,19,229-243. 

It is not necessary to carry out synthesis, if the triggering photochromic compound has good affinity to the polymer matrix. A mixture of the polyacrylate with BMAB which exhibits an excellent function as trigger is equally photoresponsive. While the monomer model compound (i.e. the acrylate before polymerization) does not provide a liquid crystalline phase, the polymer shows a clear nematic - isotropic transition at ca. 61 °C and the glass transition temperature at 24 °C as shown in Fig. 4. Tj j depends very much on the length of the alkyl spacer. In comparison with the... 

Jung, M., German, A.L. and Fischer, H.R. (2001) Polymerisation in lyotropic liquid-crystalline phases of dioctadecyldimethylammonium bromide. Colloid Polym. Sci, 279, 105-113. 

As long as the crosslinking density is low, the liquid-crystalline phases of the corresponding uncrosslinked polymer are retained for the networks [94-97], with the same structure and without large shifts of the transition temperatures (see Chap. V of this Volume). As the crosslinking density increases, the smectic phases should disappear (Table 9) for the benefit of a less-ordered nematic state [98] then all the liquid-crystalline phases should be destroyed for the most crosslinked networks, at least for materials crosslinked in an isotropic state [99-101]. Degert et al. [98] pointed out that this evolution in the mesophase stability also depends on the nature (mesogenic or aliphatic) of the crosslinks. 

The formation of liquid-crystalline phases of cellulosics, especially of the lyotropic kind, has yet to be explained. Certainly the chain stiffness may have to be taken into account as one of the factors in question, but the solvent-polymer interaetion may have to be considered as well. In the next section, models for the description of the pitch as a chiral property and models to... 

Abe, A., Furuya, H., Zhou, Z., Hiejima, T., and Kobayashi, Y, Stepwise phase transitions of chain molecules crystallization/melting via a nematic liquid-crystalline phase, Adv. Polym. ScL, 181, 121-152 (2005a). 

In this paper I will focus on how these similarities (and differences) between ordinary liquids and polymeric fluids may be transposed to liquid crystalline phases of low molar mass mesogens and their polymeric analogues. This general theme is prefaced by a brief review of the two general classes of polymeric liquid crystals that is intended for researchers unfamiliar with the development of the field. The literature citations are not comprehensive but rather are designed to enable one to assess current references to the topics considered here. The elementary physico-chemical aspects of liquid crystals — applicable to polymeric liquid crystals as well are exhaustively summarized in Kelker and Hatz s Handbook of Liquid Crystals. Blumstein has edited a text. Liquid Crystalline Order in Polymers, that reviews some of the earlier work on PLCs.(5) More recent work is summarized in Polymer Liquid Crystals edited by Cif-feri, Krigbaum and Meyer.(6)... 

Systematic investigations of the past years have proved that the structures of the liquid crystalline phases of liquid crystalline (l.c.) side chain polymers are similar to the structures of conventional lovi/ molar mass liquid crystals (1.1c). Nematic and cholesteric phases as vi/ell as S and S phases have been clearly identified The systematic realization of l.c. 

M. Doi, "Molecular Dynamics and Rheological Properties of Concentrated Solutions of Rod-like Polymers In Isotropic and Liquid Crystalline Phases," J. Polym. Sci. Polym. Phys. Ed., 19, 229-243 (1981). 

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