Mesomorphic state polyphosphazenes

The study by Percec, Tomazos and Willingham (15) looked at the influence of polymer backbone flexibility on the phase transition temperatures of side chain liquid crystalline polymethacrylate, polyacrylate, polymethylsiloxane and polyphosphazene containing a stilbene side chain. Upon cooling from the isotropic state, golymer IV displays a monotropic nematic mesophase between 106 and 64 C. In this study, the polymers with the more rigid backbones displayed enantiotropic liquid crystalline behavior, whereas the polymers with the flexible backbones, including the siloxane and the polyphosphazene, displayed monotropic nematic mesophases. The examples in this study demonstrated how kinetically controlled side chain crystallization influences the thermodynamically controlled mesomorphic phase through the flexibility of the polymer backbone. 

Second, the ability of completely aromatic polyesters to form mesomorphic structures is interesting. Obviously, in such cases, the appearance of nematic LC states seems most probable. Furthermore, some polybenzoates (3-8) show mesophases, which cannot be described in terms of the conventional classification of liquid crystals, with respect to their arrangement, and which are similar to mesomorphic structures of flexible-chain polyorganosiloxanes (9) and polyphosphazenes (10). Finally, studies of relaxations and phase transitions in rigid-chain LC polyesters, in particular, their molecular mobility in the solid state, i.e., below the melting temperature of crystalline phase, are of great interest. 

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