Crystalline polymer system

For crystalline polymer systems, transition from the crystalline structure to a mesophase structure occurs, whereas for amorphous polymer systems, the mesophase occurs after the Tg has occurred. Some polymer LC systems form several mesophases. Mesophases can be detected using DSC, x-ray diffraction, and polarizing microscopy. 

Figures 7 and 8 display such plots for various lyotropic liquid-crystalline polymer systems, which range in q from 5.3 to 200 nm. As expected, most data points come close to the theoretical curve. This finding suggests that liquid crystallinity of stiff-chain or semiflexible polymer solutions has its main origin in the hard-core repulsion of the polymers.

Fig. 12a-c. Polymer concentration dependence of the orientational order parameters S for three liquid-crystalline polymer systems a PBLG-DMF [92,93] b PHIC-toluene [94] c PYPt-TCE [33], Marks experimental data solid curves, theoretical values calculated from the scaled particle theory. The left end of each curve gives the phase boundary concentration cA... 

Wendorff, J. H. Scattering in liquid crystalline polymer systems, in A. Blumstein, ed. Liquid Crystalline Order in Polymers . Academic Press, New York, NY 1978, p. 1... 

A. I. Isayev, T. Kyu and S. Z. D. Cheng (Eds.), Liquid-crystalline Polymer Systems Technological Advances, Vol. 632, American Chemical Society, Washington, DC, 1996. 

FT-IR imaging was rapidly adopted in polymer research. For example, in 1998 Bhargava et al. reported their FT-IR imaging results of the interface of a phase-separated multicomponent polymeric system [5]. A subsequent report by Snively and Koenig in 1999 dealt with the examination of the homogeneity and the degree of orientation in semi-crystalline polymer systems, notably different poly(ethylene glycol) (PEG) systems [6]. 

The film sample investigated proved to be a semi-crystalline polymer system with a DSC Tg(onset)-value of 16°C. The DSC Tm(l)-value was 146°C with a Hf(l)-value of 18 J/g. The so-called processing-window of this polymer proved to be about 50°C, from 150°C to about 200°C. This bio-polymer proved to be (as usual) strongly moisture dependent. The equilibrium water saturation of the film in contact with water was 64 %wt., however visual detectable swellings effects were not noticed. 

CHE Cheng, L.-P., Young, T.-H., Chuang, W.-Y., Chen, L.-Y., and Chen, L.-W., The formation mechanism of membranes prepared from the nonsolvent-solvent-crystalline polymer systems. Polymer, 42,443, 2001. 

Shibaev V, Bobrovsky A, Boiko N. 2003. Photoactive liquid crystalline polymer systems with light controllable structure and optical properties. Prog Pol Sci 28 729 836. 

Zettsu N, Ogasawara T, Mizoshita N, Nagano S, Seki T. 2008. Photo triggered surface relief grating formation in supramolecular liquid crystalline polymer systems with detachable azobenzene unit. Adv Mater 20 516 521. 

The recently published reviews by Papkov on lyotropic liquid crystalline polymer systems (12 ) and by Shibaev and Plate on the liquid crystalline states in polymers (13) should be regarded as the first attempts to systematize the great body of available experimental data with a view to elaborating adequate techniques of producing liquid crystalline polymer systems. 

Chen, W. (1996) in Liquid-Crystalline Polymer Systems (ed. A.I. Isayev, T. Kyu and S.Z.D. Cheng), American Chemical Society, Washington, chapter 15], and liquid crystals (that is, condensed phases in which molecules exhibit orientational order and varying degrees of positional order [2]). The distinctions among these three mesophase types will be maintained throughout this chapter liquid crystalline systems which are thermotropic (that is, induced by changes in the temperature or pressure of a sample) rather than lyotropic (that is, induced by addition of an isotropic liquid as solvent ) will be emphasized. 

L. Tson, G. Parker, W. Chen, M. Hata, Liquid crystalline polymer systems. ACS Symp. Ser. 632, 54 (1996)... 

Nevertheless, in certain favourable cases, it has been possible to obtain composition information about polymer mixtures [128], and configuration information relating to relatively simple crystalline polymer systems [129]. The latter case is illustrated (Figure 7.8) by the spectrum of poly(ethylene adipate) where the observed spectrum is more complex than would be expected in the absence of conformational effects. 

Zettsu, N. Ogasawara, T. Mizoshita, N. Nagano, S. Seki, T. (2008). Photo-Triggered Surface Relief Grating Formation in Supramolecular Liquid Crystalline Polymer Systems with Detachable Azobenzene Units. Adv. Mater., 2008, 20, 516-521. 

In many ways, the greatest problem in the study of anisotropy in non-crystalline polymer systems in general is its definition. For example, what is meant by molecular orientation in a liquid crystal polymer in which just the side-groups are mesogenic It may imply the anisotropy in the trajectory of the molecular backbone or it could mean the alignment of the side-chains alone. In this case both measures are needed for a full description of the anisotropic molecular organization, but each measure requires careful definition. 

Firstly general mechanisms for gelation are discussed, and then examples for such mechanisms presented. In some cases, the polymer system chosen is the best example for a particular mechanism, but it may nevertheless be currently only a minority view for this polymer. Examples are drawn from both biopolymer and synthetic-polymer systems, and although the emphasis is on crystalline polymers, other systems are considered for perspective and completeness. Indeed, there are crystalline-polymer systems for which the proposed mechanism of gelation does not involve crystallization, and, conversely, there are polymers which would generally be classified as non-crystalline for which the gelation mechanism is based on limited crystallization. It is hoped that by its inherent interdisciplinary nature, this approach may provide new insights. 

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