Polyphosphazenes isotropization temperature

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. 

Polyphosphazenes are partially crystalline polymers whose degree of crystallinity is a function of the conditions of preparation of the samples. The glass transition temperature of the amorphous phase is determined by the type of substituents at the phosphorus atom. The Tg for a series of polyphosphazenes in which the existence of mesophases has been reliably established [42] are reported in Table 4.4. The two-stage transition of the crystalline phase through the mesomorphic phase into an isotropic melt was established in [41-42]. The values of the temperatures of the phase transitions for a sCTies of polyphosphazenes are reported in Table 4.4. In polyaryloxyphosphazenes, T,- are close to. 

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