Polymer, branched Liquid crystals

As with all branches of science, polymer chemistry is continually advancing. New topics in polymer chemistry which involve new concepts, new polymers or novel uses for existing materials are being studied in research laboratories throughout the world. In this chapter, some of the more important of these developments are described including the use of polymers in medicine, electronically conducting polymers, and polymer liquid crystals. 

Attaching non amphiphilic or amphiphilic liquid crystalline molecules as side chains to linear, branched or crosslinkedpolymers yields liquid crystal (l.c.) side chain polymers, which can exhibit the liquid crystalline state analogously to the conventional low molar mass liquid crystals. The l.c.-side chain polymers combine the specific, anisotropic properties of the liquid crystalline state with the specific properties of polymers. 

The second group involves polymers with three-dimensional ordering of side branches (e.g., those forming Mj-phaseXTable 5). On X-ray patterns of these polymers 3-4 narrow reflexes at wide angles are observed. As a rule, the authors define this type of structure as crystalline, or ascribe a smectic type of structure, characteristic for ordered smectics in SE or SH phases. The heats of transition from anisotropic state to isotropic melt are usually small and do not exceed the heats of transition smectic liquid crystal — isotropic melt . The similarity of structural parameters of three-dimensionally ordered smectics and that of crystalline polymers of the type here considered, make their correct identification quite a difficult task. 

The example of the above mentioned specific features of low-molecular liquid crystals, capable of orientation in an electric field, has led recently to the synthesis of a series of acrylic, methacrylic and siloxane polymers and copolymers of nematic and smectic types with nitrile end groups in the side branches (see Tables 3, 4, 9, 12) ... 

In another example, Sarcocine-NCA prepared by phosgenation of sarcosine, followed by cyclisation in the presence of triethyl amine is used for the preparation of lipopeptide-based branched polymers forming thermotropic and lyotropic liquid crystals as shown in scheme 197 (Ref. 248). 

Poly(El) and related compounds has become important in industrial, agricultural, and biological fields. Conventional poly(El) [l] obtained from ethylenimine (El) is, however, amorphous, or sticky liquid if it is a low molecular weight material, because many branches along the polymer chain suppress crystallization (l-5). On the other hand, poly(El) [II] obtained from 2-oxazoline, which was first prepared by Saegusa et al. (6), is highly crystalline owing to the linear structure. 

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