Liquid crystalline polymers characterization methods

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. 

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). 

The unique capabilities of solid-state deuteron NMR (as well as experiments with N and result from the ability to assess ordering and mobility of individual bonds in a solid material. One can specifically examine the molecular mechanisms that determine bulk properties. This ability has motivated deuteron studies of such fundamental issues as the nature of the glass-transition [10-18] interactions in blends and mixtures [19-26], the molecular ordering and dynamics of crystalline materials [10,11,27-31] dynamics of elastomers [32-45], dielectric properties [46,47] and mechanical spectroscopy [48-51]. New experiments continue to be tied to methods development, particularly in the areas of multi-dimensional NMR [10,11,46, 52-61]. Recently, deuteron NMR has been employed in the characterization of new materials, for example for new liquid crystalline polymers [62-84],... 

The mesophase exhibiting a homeotropic texture can still shew stir opalescence, which is a method of identification particularly suited for thermotropic polymers. This somewhat crude method of characterizing a liquid crystalline material is performed by shearing a thin film of the mesophase and looking for momentary appearances of turbidity in the otherwise transparent melt. No microscope is need to observe stir opalescence, but simple shearing of the homeotropic melt between crossed-polars can also reveal the mesophase. 

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... 

The objectives in this chapter are to describe, with examples, the group of experiments that is now available for study of a new material with deuteron NMR. The focus is upon methods for the characterization of order and mobility in the crystalline state or below Tg, which is our own interest. To be comprehensive, the literature of experiments associated with networks and liquid crystalline materials have been referenced. Examples are taken from the study of the conducting polymer poly(p-phenylene vinylene) carried out in the laboratory of F.E. Karasz at the University of Massachusetts [85-89]. Special attention is also given to several recent experiments from the laboratories of G. Zachmann [31], A. English [92-97] and H.W. Spiess [10, 11, 46, 53]. The focus is upon the means and criteria that motivate one to choose deuterium NMR for characterization. 

Rods and Helices.—Because of the considerable advances being made in biopolymer characterization, theories and experimental methods particularly applied to stiffened chains and wormlike models, as well as to polyelectrolytes, have continued to proliferate. At the same time work has continued to progress in the synthesis and description of novel synthetic rod-like polymers, many of which have interesting liquid crystalline properties. The publication of the proceedings of a recent conference devoted to the latter materials provides a state of the art description of work in this field. 

In the present work, terephthalic acid was successfully regenerated from PET waste bottles via saponification process in high yield and purity. The new liquid crystalline poly(azomethine esters) based on terephthalic acid were prepared and characterized successfully using important and vital spectroscopic methods. The combining results that obtained from DSC, POM and XRD studies were confirmed the liquid crystallinity of the poly(azomethine esters). AU the polymers exhibit nematic mesophases except that for polymer 3(a). Furthermore, TGA results also confirmed that the new synthesized polymers possess high thermal stability. 

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