Condensation polymers liquid-crystalline

Combined liquid crystalline polymers, 49 Combustion testing, 245 Composites, thermoplastic, 32 Compression force deflection (CPD), 244 Compression tests, 242 Condensation... 

Preston, J. Synthesis and properties of rodlike condensation polymers. A. Blumstein, ed. Liquid Crystalline Order in Polymers . Academic Press, New York 1978, pg. 141... 

The development is reviewed of liquid-crystalline polymers whose mesophase formation derives from the nature of the chemical units in the main chain. The emphasis lies primarily on highly aromatic condensation polymers and their applications. The general properties of nematic phases formed by such polymers are surveyed and some chemical structures capable of producing nematic phases are classified in relation to their ability to form lyotropic and thermotropic systems. The synthesis, properties, physical structure and applications of two of the most important lyotropic systems and of a range of potentially important thermotropic polymers are discussed with particular reference to the production and use of fibres, films and anisotropic mouldings. 

The first reported thermotropic and lyotropic liquid-crystalline poly(aryleneethynylene)s were not parent PPEs, but organometallic derivatives 65 made by the Pd-catalyzed condensation of Vollhardt s diethynyl 64 with diiodobenzenes 46 [45]. The polymers were isolated in good to excellent yields as amorphous tan or red powders with moderate Pn values of... 

Liquid crystallinity can be attained in polymers of various polymer architectures, allowing the chemist to combine properties of macromolecules with the anisotropic properties of LC-phases. Mesogenic imits can be introduced into a polymer chain in different ways, as outhned in Fig. 1. For thermotropic LC systems, the LC-active units can be connected directly to each other in a condensation-type polymer to form the main chain ( main chain liquid crystalline polymers , MCLCPs) or they can be attached to the main chain as side chains ( side chain liquid crystalline polymers , SCLCPs). Calamitic (rod-Uke) as well as discotic mesogens have successfully been incorporated into polymers. Lyotropic LC-systems can also be formed by macromolecides. Amphiphihc block copolymers show this behavior when they have well-defined block structures with narrow molecular weight distributions. 

Before these results were published, polymer physicists and chemists mainly investigated only two phase-states, amorphous and crystalline. At the present time, along with these two states, the third phase-state of condensed systems, i.e. the liquid crystalline state, became very important. Here the situation turned out to be the same as in the case of low molar mass liquid crystals. In spite of the fact that historically the low molar mass substances in liquid crystalline state had been known for about a century, the intensive study of their properties began only after they had found an important practical application owing to a sharp change in optical properties of liquid crystals in electromagnetic fields (for visual displays) and as sensitive temperature indicators (in medicine). 

An interesting class of condensation copolymers is the liquid crystalline polymers (LCP). From the viewpoint of practical applications, LCP are very attractive as... 

Several examples are known, in which one or even both monomers in a liquid crystalline [A-B]n condensation polymer contain cyclo-aliphatic rings [50]. The trans chair form makes a larger contribution than the cis boat form. 

A complete characterization of liquid crystalline polymers should include at least two aspects the characterization of the molecular structure and that of the condensed state structure. Since the first characterization is nothing more than what is practiced for non-liquid-crystalline polymers, we will restrict the discussion to only a short introduction of methods mostly used in the characterization of the presence and the main types of polymeric liquid crystal phases. The methods include the mostly used polarizing optical microscopy (POM, Section 4.1), differential scanning calorimetry (DSC, Section 4.2) and X-ray diffraction (Section 4.3). The less frequently used methods such as miscibility studies, infrared spectroscopy and NMR spectroscopy will also be discussed briefly (Section 4.4). 

When a polymerization is accompanied by phase transition, the overall thermodynamic parameters are the sum of parameters of the chemical reaction and phase transition (cf. p. 11). Thus, for instance, thermodynamics of polymerization in the crystalline state from a liquid monomer will be given by the thermodynamics of formation of the amorphous (condensed) polymer and polymer crystallization, provided, that polymerization proceeds in the solid state with monomer packing in the crystalline state simultaneously with propagation. 

Livolant F, Leforestier A (1996) Progress in Polymer Science 21 1115 (a) Economy J, Goranov K (1994) Advances in Polymer Science 117 221 (b) Preston J (1978) Synthesis and properties of rod-like condensation polymers. In Blumstein A (ed) Liquid crystalline order in polymers. Academic Press, New York... 

Chen, W. (1996) in Liquid-Crystalline Polymer Systems (ed. A.I. Isayev, T. Kyu and S.Z.D. Cheng), American Chemical Society, Washington, chapter 15], and liquid crystals (that is, condensed phases in which molecules exhibit orientational order and varying degrees of positional order [2]). The distinctions among these three mesophase types will be maintained throughout this chapter liquid crystalline systems which are thermotropic (that is, induced by changes in the temperature or pressure of a sample) rather than lyotropic (that is, induced by addition of an isotropic liquid as solvent ) will be emphasized. 

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