Thermotropic LCPs crystalline polymers

Figure 1.69 General structure of main-chain (M.C.) and side-chain (S.C.) LCPs. Adapted from T. S. Chung, The recent developments of thermotropic liquid crystalline polymers. Polymer Engineering and Science, 26(13), p. 903. Copyright 1986, Society of Plastics Engineers.

Thermotropic liquid crystalline polymers (LCP) show during heating one or more mesophase transition effects before they change after an endothermic fusion maximum into an isotropic melt. These transition effects are usually indicated by Tm,... 

New opportunities of blending polyolefin can be seen in thermotropic liquid crystalline polymer (LCP) multicomponent, automobile fuel tanks, polymer solar cells, chemical sensors, polymer membrane, and foams. 

Three commercially available thermotropic liquid crystalline polymers (TLCPs) were presented as examples in this section. They are Hoechst Celanese Vectra A950 and Vectra B950 as well as Amoco Xydar . Vectra A950 is a random copolymer of 73 mol% 4-hydroxybenzoic acid and 27 mol% 6-hydroxy-2-naphthoic acid, and Vectra B950 is a random copolyesteramide consisting of 60 mol% of 6-hydroxy-2-naphthoic acid, 20 mol% terephthalic acid, and 20 mol% p-aminophenol. Xydar is made from p-hydroxybenzoic acid, isophthalic and/or terephthalic acids, and 4,4 -biphenol. The repeating unit structures of the three LCPs are shown in Figure 6.2. 

The zero shear viscosity scales with Nf" to contrast Af dependence for isotropic polymers [20] So far, we have examined the dynamics of rod-Uke macromolecules in isotropic semi-dilute solution. For anisotropic LCP solutions in which the rods are oriented in a certain direction, the diffusion constant increases, and the viscosity decreases, but their scaling behavior with the molecular weight is expected to be unchanged [2,17], Little experimental work has been reported on this subject. The dynamics of thermotropic liquid crystalline polymer melts may be considered as a special case of the concentrated solution with no solvent. Many experimental results [16-18] showed the strong molecular weight dependence of the melt viscosity as predicted by the Doi-Edwards theory. However, the complex rheological behaviors of TLCPs have not been well theorized. 

It has been well recognized that melt blending of a thermotropic liquid crystalline polymer (LCP) and an isotropic polymer produces a composite in which fibrous LCP domains dispersed within the blend act as a reinforcement il ). The so-called insitu composite possesses several advantages in comparison with the inorganic reinforced thermoplastic composites. Firstly, LCP lowers the blend viscosity in the actual fabrication temperature range (3-5), Hence, the enhanced processability endows moldability for fine and complex shaped products. 

The preparation methods and the novel permselective characteristics of (polymer/LC) composite films have been extensively studied (1-3). Also, various types of (polymer/LC) composite systems have been reported as large area and flexible light-intensity controllable films (4-11). Since thermotropic liquid crystalline polymers (LCPs) with mesogenic side chain groups exhibit both inherent mesomorphic properties of LC and excellent mechanical characteristics of polymeric materials, LCPs... 

Thermotropic liquid crystalline polymers can be formulated with high concentration of glass fiber to withstand working temperatures in excess of 300"C. In processing LCP, one problem arises. LCP orients itself in the direction of shear or flow - the process which benefits many materials but makes products from pure LCP excessively anisotropic. To balance mechanical properties it has been suggested that some quantities of short glass or mineral fibers be added to LCP. 

These data illustrate how in situ x-ray scattering allows detailed, quantitative measurements of the orientation state in thermotropic liquid crystalline polymers under flow. Unlike model lyotropic LCPs, the model thermotropic PSHQ-6,12 and... 

Hashimi S, Takeshi K (2007) Shear rate dependence of viscosity and first nramal stress difference of LCP/PET blends at solid and molten states of LCP. J Appl Polym Sd 104 2212-2218 Hsies TT, Tiu C, Simon GP, Wu RW (1999) Rheology and miscibilily of thermotropic liquid crystalline polymer blends. J Non-Newt Fluid Mech 86 15-35 Isayev A1 (2012) Liquid crystalline composite. In Luigi N, Borzacchiello A (eds) Wiley Encyclopedia of composites, 2nd edn. Wiley, New York Isayev AI, Nicolais L (2011) Liquid crystalline composite. Wiley Encyclopedia of composites. Wiley, New York... 

Thermotropic liquid crystalline polymers (TLCPs) have gained increased commercial attention because of their unique properties. These include their low coefficients of thermal expansion, low viscosity, and high modulus, low permeability to gases, low dielectric constants, and chemical resistance. As the demand for these characteristics increases, it is anticipated that the use of TLCPs will grow, rising at a projected annual growth rate of 25 % from an estimated use of ten million pounds in recent years. In expanding the potential uses for TLCPs, it has been found that TLCP/TLCP blends can possess characteristics which are better than those of either individual TLCP (Utracki and Favis 1989). But the better result is only possible if the LCP fibrillation is prominent in the blend system. 

Plummer CJG, Ziille B, Demarmels A, Kausch HH (1993) The stracture of filled and unfilled thermotropic liquid crystalline polymer injection moldings. J Appl Polym Sci 48(5) 751-766 Popa-Nita V, Gerlic I, Kralj S (2009) The influence of disorder on thermotropic nematic liquid crystals phase behavior. Int J Mol Sci 10(9) 3971-4008 Qin Y, Brydon DL, Mather RR, Wardman RH (1993) Fibres from polypropylene and liquid crystal polymer (LCP) blends 1. Effect of LCP concentration. Polymer 34(6) 1196-1201 Rath T, Kumar S, Mahaling RN, Mukherjee M, Das CK, Pandey KN, Saxena AK (2006) Flexible composite of PEEK and liquid crystalline polymer in presence of polyphosphazene. J Appl Polym Sci 104 3758-3765... 

Solution behavior occupies a central position in polymer science. Here we briefly review some recent results for th solution properties of main chain thermotropic liquid crystalline polymers (LCPs) dissolved in liquid crystalline solvents. We concentrate on the distortional properties of such LCPs. 

Traditionally, two major classes of thermotropic liquid crystalline polymers have been identified the so called main chain (longitudinal) and side chain (comb) types (MCLCPs and SCLCPs, respectively) (Fig. 2.5). More recently other variants have appeared these are combined LCPs which are hybrid between MCLCPs and SCLCPs, and the rigid rod types described by Watanabe et A great wealth of literature already exists in the form of unified texts and reviews which detail both the major classes of LCPs. Bibliographic data have been compiled" and reviews more or less specific to main chain or comb " polymer systems have appeared. We shall be concerned here only with main chain and side chain LCPs. 

The effect of shear on the temporal development of phase separation in thermotropic liquid crystalline polymer (LCP)/polycarbonate (PC) blends was examined. Experiments were performed using a polarized-hght microscope, equipped with a shearing hot stage. Phase separation, with and without shear, in blends containing 50 wt % TCP were analyzed. The results showed that the speed and amount of phase separation increased when shear was applied. 

Liquid crystalline polymers (LCPs), 49 melt rheology of, 52 Liquid crystalline (LC) state, 48-49 Liquid crystalline thermotropic polyesters, 20... 

Research on liquid crystalline polymers(LCP) is a fashionable subject with the goal of developing speciality polymers of superior mechanical and thermal properties. Besides these properties, other interesting properties of LCP have not been fully utilized. We are trying to use thermotropic LCP for photon-mode image recording material. 

Liquid crystal polymers (LCP) are polymers that exhibit liquid crystal characteristics either in solution (lyotropic liquid crystal) or in the melt (thermotropic liquid crystal) [Ballauf, 1989 Finkelmann, 1987 Morgan et al., 1987]. We need to define the liquid crystal state before proceeding. Crystalline solids have three-dimensional, long-range ordering of molecules. The molecules are said to be ordered or oriented with respect to their centers of mass and their molecular axes. The physical properties (e.g., refractive index, electrical conductivity, coefficient of thermal expansion) of a wide variety of crystalline substances vary in different directions. Such substances are referred to as anisotropic substances. Substances that have the same properties in all directions are referred to as isotropic substances. For example, liquids that possess no long-range molecular order in any dimension are described as isotropic. 

Perhaps the most widely utilized (and studied) lyotropic LCP is poly j -phenylene terephthalamide (PPTA), more commonly known as Kevlar (see Figure 1.70). Kevlar belongs to the class of aramids that are well known for their LCP properties. Because these polymers are crystalline in solution, they are often spun into filaments, from which the solvent is subsequently removed in order to retain the aligned polymer structure. The result is a highly oriented, strong filament that can be used for a wide variety of structural applications. Most thermotropic LCPs are polyesters or copolymers that can be melted and molded into strong, durable objects. 

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