Liquid crystalline polymers solid state structures

Molecular recognition directed self-assembling of organized phases has been described recently in the formation 1) of mesophases by association of complementary molecular component, as in 13 (23) 2) of supramolecular liquid crystalline polymers of type 14 (24) and 3) of ordered solid state structures, such as that represented by 15 (25). In all these cases, the incorporation of NLO active groups may be expected to produce materials whose SHG properties would depend on molecular recognition induced self-organization. 

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). 

High resolution solid-state NMR spectroscopy is also a very powerful method for characterizing the solid structure and the local motion of different solid polymers. We recently characterized the crystalline-noncrystalline structure for different crystalline and liquid crystalline polymers, such as polyolefins [7-12], polyesters [13-15], polyether [16], polyurethanes [17, 18] and polysaccharides, including cellulose [19-29], amylose [30, 31] and dextran [32]. On the basis of these analytical methods, we also investigated the intra- and intermolecular hydrogen bonds of PVA in both crystalline and noncrystalline regions as well as in the frozen solution state. In this chapter. 

For example, if the time for the process to occur is faster than the longest relaxation time, then the fluid behaves more like an elastic solid. For the liquid crystalline systems there seems to be two relaxation times which are important. One is the time for relaxation of orientation and the other is the time for relaxation of stress. Whereas these phenomena are connected for flexible chain polymers, they seem to separate for liquid crystalline polymers. In other words, there are several stress free states for LCP. Some of the behavior observed may be partly due to the copolymer nature of thermotropic systems. However, the lyotropic systems based on the polyamide structure also exhibit similar behavior. 

Liquid crystalline polymers have been discussed in many texts and review papers [65, 400-413] during the last decade, in which the synthesis, processing, morphology, orientation and structure-property relations are described. The major applications of these materials have been as high modulus fibers and films, with unique properties due to the formation of ordered lyotropic solutions or thermotropic melts which transform easily into highly oriented, extended chain structures in the solid state. 

Liquid crystalline polymers (LCPs) are best thought of as being a separate, unique class of TPs. Their molecules are stiff, rodlike structures organized in large parallel arrays or domains in both the melted and solid states. These large, ordered domains provide LCPs with characteristics that are unique compared to those of the basic crystalline or amorphous plastics (see Table 2-9) [2]. 

While the term strain hardening is widely used to describe the extensional flow behavior of some polymeric liquids, it lacks any basis in polymer physics. It was introduced by G. I. Taylor in 1934 [ 155] to describe the plastic flow of crystalline metals. It has also been used to describe the behavior of glassy and semicrystalline polymers, where it is said to arise from the effect of strain on solid-state structural features. Its use for melts is based solely on the shape of the curve of 7] (t,e) versus time with strain rate as a parameter. At small values of strain (e =t e) the behavior follows the prediction of linear viscoelasticity, as indicated by Eq. 10.93. Dealy... 

Liquid crystalline aromatic polyesters are a class of thermoplastic polymers that exhibit a highly ordered structure in both the melt and solid states. They can be used to replace such materials as metals, ceramics, composites and other plastics... 

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