Mesomorphic polymers

Attard GS, Garnett S, Hickman CC, Imrie CT, Taylor L (1990) Liq Cryst 7 495 Shibaev VP, Lam L (eds) (1994) Liquid crystalline and mesomorphic polymers. Springer, BerUn Heidelberg New York... 

Provder, T. 2006. Film Formation, Process, and Morphology. Oxford University Press, New York. Rudin, A. 1998. Elements of Polymer Science and Technology, 2nd ed. Academic, Orlando, EL. Shibaev, V. and Lam, L. 1993. Liquid Crystalline and Mesomorphic Polymers. Springer, New York. Sinha, R. 2002. Outlines of Polymer Technology Manufacture of Polymers and Processing Polymers. Prentice-Hall, Englewood Clifts, NJ. 

Shibaev, V. and Lam, L. 1993. Liquid Crystalline and Mesomorphic Polymers. Springer, New York. Svenson, S. 2006. Polymeric Drug Delivery I and II. Oxford University Press, New York. 

The development of blends and polymer mixtures is a rapidly expanding field. Indeed, a mixture is often a simple way to obtain an ensemble of properties so that a high-performance material corresponding to a given application can be constructed with a cost only slightly higher than that of the constituents. Non-mesomorphic polymer mixtures have been extensively studied (29-311. particularly their thermodynamic stability. Incompatibility is the rule in most cases, especially for high molecular masses of the constituents, unless specific interactions exist between the different constituents. 

Strzelecki has studied the orientation of a nematic polymer in its LC state in a 0.3 T magnetic field by X-ray diffraction and found that the sample had an order parameter of 0.64 The orientation of LC polymers in a magnetic field has also been observed by others using X-ray techniques I Extruded fibers have been studied by Roviello and Sirigu to measure the degree of orientation achievable in mesomorphic polymers by shear field, but only solid samples were studied and even though they were oriented, the results gave little quantitative indication of the order of the mesophase... 

Plots of -a against phenyl content for n-hexane and benzene probe-solutes, provided in Figure 4, emphasize the dependency of the family-plot slopes of aliphatic and aromatic compounds (particularly those of the former) on the aromatic content of the OV solvents. The aromatic character of these stationary phases can therefore be gauged simply with the retentions of a few hydrocarbons. Presumably, with judicious choice of the probe-solute, other properties of polymer GC phases could be deduced from the slopes a of Equation 16 in a similar way. Family plots have also been shown recently to reflect discontinuities in retentions due to phase changes in mesomorphic polymers (16). 

Liquid crystalline imprinted materials have been synthesized (Fig. 24) from polysiloxanes with mesogenic side-chains. In some of them, acetophenone was chosen as template and was covalently linked to the mesomorphous network via a ketal link [ 199]. In the others, the templates (carbobenzoxy-L-phenylala-nine, 1,8-diaminonaphthalene or theophylline) were in interaction with the mesomorphous polymer via hydrogen bonding [200]. All the imprinted networks were obtained as dense membranes. 

Completely new a ects came into this field with the development of LCPs. Generally, conventional non-mesomorphic polymers play an important role in many technological areas, as deduced from their countless applications [17]. In particular, by exploiting the variety in chemical structures polymeric materials with quite different macroscopic properties can be produced. Here, the realization of LCPs offers new and interesting scopes of tedmolo cal applications, based on the unique combination of specific polymer features with the anisotropic properties of the LC state [18-21]. 

During the last years most efforts at preparing LCPs have focused on the use of rod-like mesogens. Only very recently has the synthesis of mesomorphic polymers with disclike units (see Fig. 1) been reported [29,30]. Likewise, combing main-chain/ side-chain polymers (see Fig. 1), comprising structural aspects of both types of LCPs, have only recently become known [31]. 

The typical LCP character, resulting from the combination of LC and polymeric features, is primarily reflected in the phase behaviour. In analogy to LMLCs, LCPs exhibit various mesophases (see Fig. 2), often broadened in comparison to those of the monomeric systems. Likewise, the polymeric nature also dominates the behaviour in the solid phase below the anisotropic melt. Here, semicrystalline or glassy states are reported, which are very common for conventional non-mesomorphic polymers. 

There is a strong interest to prepare molecular conductors inside an anisotropic structural organization, which could be liquid crystals, mesomorphic polymers or Langmuir-Blodgett (LB) films. 

We have shown that this classification is sufficiently simple and general to include most important polymer solid mesophases identified so far. We are aware, however, that our classification of mesomorphic polymers, as well as alternative ones based on the different kinds of disorder which may occur in crystalline polymers, may not be exhaustive, since in many cases different kinds of disorder are interrelated and simultaneously present. For instance, in the case of polyacrylonitrUe, the irregular configuration of chains deter-... 

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. 

P-IOMBT in dichloroacetic acid was investigated in an alternating electric field. Experimental data show that the molecules of this polymer, just as those of other mesomorphic polymers, are characterized by a relatively high Kerr constant and the corresponding high dipole moment and orientational polar order. 

Molecular theories of mesomorphic polymers may serve to give a better insight into the mechanisms involved in the formation of ordered phases in macromolecular liquids. The importance of parameters such as chain length, chain flexibility... can be explored and the results used in synthesis of new systems with well-defined characteristics. Studies of the influence of solvents on the mesomorphic phase transition and the possibility of ordering by external fields (electric, magnetic, flow) are problems of technological in-ter>est in the spinning of fibers and in the formation of new polymer blends. 

The chain flexibility can be a function of temperature or solvent concentration and possible conformational changes in mesomorphic polymers have been both predicted by theoretical calculations and observed in experiment. The elastic chain model takes intrachain interactions into account in a very simple way but neglects fine details of macromolecular structure. We present some results within this model for liquid crystalline behaviour and finally... 

Polymer solutions and blends have been extensively studied,motivation being both the fundamental and technological interest 2. When one component is a liquid crystal polymer, synergy could produce exceptional properties due to the anisotropy of the mesomorphic polymer. It is important to determine the conditions for the existence of either a uniform, mesomorphic phase or an incompatible biphasic system. In such studies, the rigid or semi-rigid character of the chains and the anisotropic interaction between the chains play a role. The presence of mesomorphic macromolecules is labeled by their ability to align under certain conditions, a fact which can be exploited in the experimental determination of phase diagrams. 

Ganicz, T. and W.A. Stanczyk. 2003. Organosflicon mesomorphic polymer systems. Prog Polym Sci 28 303. 

It was also shown that it is possible to synthesize polymethacrylate liquid crystal polymers with mesomorphic properties that contain ferrocenes with two flexible chains at the 1,1 -positions [59]. Based on dilatometric measurements, a head-to-tail molecular arrangement of the monomeric units occurs within the smectic A phase. Because of special electrochemical properties of ferrocene, these materials are of interest for developing electroactive mesomorphic polymers. The structure of the polymer can be shown as follows [59] ... 

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. 

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