Thermotropic liquid-crystalline polymers interest

There has been a great deal of interest in thermotropic, liquid crystalline polymers in the past twenty years or so since the discovery of useful materials based on them. Many critical factors such as structure of mesogenic units, presence and structure of flexible spacers or rigid kinks, molecular weight and its distribution, and thermal history influence thermal, physical and thermotropic properties of liquid crystalline polymers(1-13). 

The interest in thermotropic liquid-crystalline polymers has grown in recent years due to the their inherently high stil ess and strength, high use temperatures, excellent chemical resistance, low melt viscosity and low coefficient of thermal expansion. 

There has been considerable interest in recent years in the study of liquid crystalline order in polymeric materials. Following on from the use of small molecules in display applications, the possibility of creating polymers with similar characteristics became attractive. Onsager and Flory predicted that rigid rod-like macromolecules should form liquid crystalline phase. However, it was not until 1975 that the first observation of a thermotropic liquid crystalline polymer was reported. Several reviews have been published on polymeric liquid crystals. ... 

Another interesting approach to improve mechanical properties of FDM materials is presented by Gray et who developed a composite material constimted from polypropylene (80wt.%) and a thermotropic liquid crystalline polymer (20wt.%). The composite can be processed in conventional FDM machines and exhibits significantly superior mechanical properties in comparison to commercially available materials such as ABS. Preparation of feedstock filaments involves an elaborate dual-extmsion process. 

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. 

Academic and industrial interest in liquid-crystalline polymers of the main-chain type has been stimulated by certain special properties shared by lyotropic and thermotropic systems that exhibit a nematic phase. Although these special properties affect both the processing into fibres and other shaped articles and the physical behaviour of the products, the product behaviour is at least partly attributable to the novel processing behaviour. 

Liquid crystalline polymers (LCPs) have gained attraction as materials with interesting optical, mechanical and rheological properties [3-7]. This review summarizes research on thermotropic liquid crystalhne polymers synthesized by metathesis routes, as this chemistry has proven to be a versatile way to build up well-defined polymer architectures [8]. Recent results promise to ejq)and the possible uses of these methods. 

The phase behavior is similar to that of a lower critical solution temperature (LCST), hence it is different from the above systems. The HPC/water system is an interesting model system because of the rich variety of phase structure 01 the material. HPC is a semicrystalline polymer in the solid state (7), but exhibits thermotropic liquid crystalline character at elevated temperatures below the melting point (8). It shows isotropic phase in dilute solutions, but forms an ordered liquid crystalline phase with cholesteric structure in concentrated solutions (4). 

The homopolyestcr of 4-hydroxybcnzoic acid and its copolyestcrs with 6-hydroxy-2-naphthoic acid and with 4,4 -biphenol and tcrephthalic acid are of continuing commercial and academic interest. (1,2) From the applications side, interest stems from the high moduli and high temperature properties of these polymers, while on the fundamental side, interest arises from the main-chain thermotropic liquid crystalline... 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

Thermotropic liquid crystal polymers (LCI ) are of considerable current interest, because of their theoretical and technological aspects [1-3]. Evidently, a new class of polymers has been developed, combining anisotropic physical properties of the liquid crystalline state with diaracteristic polymer features. This unique combination promises new and interesting material properties with potential ai lications, for example in the field of high modulus fibers [4], storage technology, or non-linear optics [5]. 

Schiffbase ligation has attracted significant attention as a method for creating coordination polymers with interesting morphological, catalytic, or conductive properties. For example, a series of well-characterized, thermotropic, liquid-crystalline... 

From practical considerations, two properties are of prime interest The effect of liquid crystalline behavior on viscosity and the ability of the polymer to retain the ordered arrangement in the solid state. Liquid crystalline behavior during the melt results in lower viscosity, because the rigid polymeric mesophases align themselves in the direction of the flow. As a result, the polymer is easier to process. Also, retention of the arrangement upon cooling yields a material with greatly improved mechanical properties. Several thermotropic liquid crystalline copolyesters are now available commercially. 

Thermotropic, main-chain, liquid-crystalline polymers (LCPs) have attracted considerable attention as a result of their high stiffness and mechanical properties. There has been interest in combining the LCPs with other materials. In one area, LCPs are used, in relatively low concentration, to reinforce less-stiff materials. In another case, a second component is used as a solvent to increase the mobility in the LCP and form lyotropic liquid-crystalline materials. There are now two reports, from Kricheldorf s group, of blends of PCL with liquid-crystalline polyesters [156,157]. 

There is currently considerable interest in the solid state physics of thermotropic liquid crystalline (LC) polymers and much emphasis is placed on studies regarding the solid-solid transitions and the chain dynamics of these systems. Recently, evidence for the occurrence of supercooled mesomorphic structures in the glassy state of polymers quenched from the anisotropic melt has been presented. ... 

Aromatic liquid crystalline (LC) copolyesters of commercial importance are made by processes which produce compositionally heterogeneous chemical sequences along the polymer chain. Such chemical heterogeneity is responsible for a number of interesting properties of thermotropic LC polymers. These properties include a small amount of 3Current address General Electric Plastics, Mount Vernon, IN 47620... 

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