Noncrystalline polymers local structure

The existence of pure amorphous bulk polymers has been a controversial issue since the beginning of polymer science. Natural rubber yields an X-ray pattern tiiat contains only amorphous halos, typical of any liquid. Nevertheless, it was difficult for many scientists to believe that molecules with a polymeric chain structure could pack in a truly amorphous way. There are still papers that are submitted for publication that assert that amorphous rubbery polymers are actually composed primarily of microcrystalline domains. This issue has been clarified by the incisive theoretical and experimental work of Flory. It is now understood that there are polymers that exhibit liquid crystalline phases upon melting of the crystals. The nature of the noncrystalline state of pure bulk polymers depends on tiie detailed local structure of the chain and the ratio of die persistence lengtii of die chain to the diameter of the mer. Molecules that are conformationally dexible enough to have a small persistence length can exist in the amorphous liquid state. 

Many polymers exhibit multiple relaxation processes. For those polymers that are partially crystalline such as polyesters, the interpretation is quite simple relaxation in the crystalline and noncrystalline domains have different dynamic parameters so that their respective relaxation processes occur at different experimental conditions. Acrylic polymers are not though to be partially crystalline, although there is some evidence to suggest that there may be a considerable amount of local structure. Not all acrylic polymers have two dispersions, those with short side chains exhibit two dispersions while those with longer side chains have only one, as the following results demonstrate. 

A framework is introduced, within which we may begin to discuss usefully the local molecular arrangements of noncrystalline polymers. The statistical structure is partitioned into intrachain or conformational, orientational, and spatial interchain parameters. The procedures which initially employ the comparison of the experimental intensity data with scattering functions derived from molecular models, are described with reference to natural rubber. This is seen as a "typical" polymer system. More complex chemical configurations are considered. Both poly(a-methylstyrene) and the phenylene range of polymers appear to exhibit distinct and additional local correlations. The role of these special correlations within the general framework of noncrystalline polymers is discussed. 

We now have a quantitative intensity function free from experimental aberrations. The remaining sections are concerned with detailing how such functions may be used to extract useful and detailed structural information relating to the local molecular organization of noncrystalline polymers. 

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. 

Hence, the adduced above results shown that the main factor, influencing on molecular mobility level in HDPE noncrystalline regions, is these regions structure, characterized by fractal dimension or relative fraction of local order regions (clusters) (p j. Definite influence is exercised by molecular characteristics, especially if to take into account, that between and (p, on the one hand, and S and C, on the other hand, the close intercommunication exists (see, for the example, the Eqs. (1.11) and (1.12)). As consequence, the equations using, taking into account their structural state, will be correct for polymers dimension estimation [38]. 

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