Segmented-Chain Liquid-Crystalline Polymers

These are liquid-crystalline polymers consisting of an alternate sequence of rigid and flexible molecular sections. Virtually aU segmented-chain liquid-crystalline polymers are polycondensated. 

FIGURE 5.7 Schematic Representation of typical, (partially) electroluminescent LC polymer architectures. (a) Rodlike structure, (b) Hairy-rod structure, (c) Combined main-chain-side-chain system, (d) Semiflexible segmented structure, (e) Semiflexible segmented structure with disklike mesogen. (After Weder, C. and Smith, P., Main-chain liquid-crystalline polymers for optical and electronic devices, in Encyclopedia of Materials Science and Technology, Buschow, K.H., Cahn, R.W., Flemings, M.C., Ilschner, B., Kramer, E.J., and Mahajan, S., Eds., Elsevier Science, New York, 2001.)... 

Sirigu, A., Segmented-chain liquid crystal polymers, in Liquid Crystallinity in Polymers, Ciferri, A., Ed. VCH, New York, 1991. 

Huang W, Han CD (2006b) Dispersion characteristics and rheology of organoclay nanocomposites based on a segmented main-chain liquid-crystalline polymer having side-chain azopyiidine with flexible spacer. Polymer 47(12) 4400 410... 

A block copolymer composed of liquid crystalline polymer (LCP) segments or that composed of segments having an LCP unit in their main chain or side chain was synthesized [67,68]. The latter showed partial compatibility and second-phase separation even when in a melt liquid crystalline state. 

G Liissem, R Festag, A Greiner, C Schmidt, C Unterlechner, W Heitz, JH Wendorff, M Hopmeier, and J Feldmann, Polarized photoluminescence of liquid-crystalline polymers with isolated aryle-nevinylene segments in the main-chain, Adv. Mater., 7 923-928, 1995. 

Three major topics of research which are based on phase transfer catalyzed reactions will be presented with examples. These refer to the synthesis of functional polymers containing functional groups (i.e., cyclic imino ethers) sensitive both to electrophilic and nucleophilic reagents a novel method for the preparation of regular, segmented, ABA triblock and (A-B)n alternating block copolymers, and the development of a novel class of main chain thermotropic liquid-crystalline polymers, i.e., polyethers. 

In a very crude sense, liquid crystalline polymers can be regarded as a freely-jointed-rod chain, shown in Figure 2.16. The freely-jointed-rod chain consists of a series of repeated segments of length lo- Each segment is able to rotate freely. It is assumed that the freely-jointed-rod chain is a replica of its small molecular mass liquid crystal counterpart in the liquid crystalline properties. 

It is understood that the extension of a freely-jointed-rod chain along the director is due to the preferred orientation of each segment. The maximum (R2) is less than Nl2, which is a result of random walk. In other words, a freely-jointed rod chain cannot produce the rod-like conformation expected for liquid crystalline polymers at low temperature. 

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