Studies of the Phase Transitions in Poly[bis-(4-ethylphenoxy) phosphazene] and Poly[bis-(4-t-butylphenoxy)phosphazene] I. sup (31) P NMR Study.

The solid-liquid crystalline phase transition of poly[bis- (4-ethylphenoxy)phosphazene] (PBEPP) has been studied by solid state sup (31) P NMR. The glass transition of poly[bis-4- t-butylphenoxy)phosphazene] (PBTBPP) has also been studied. There are a number of transitions in PBEPP which strongly depend on thermal history. The highest pre-melt transition T(1) around 100C is assigned to the solid to liquid crystalline transition from the abrupt change in the mobility of the PBEPP backbone observed by sup (31) P NMR. Three resonances having different chemical shifts are observed at room temperature (below T(1)) in PBEPP and assigned to the crystalline, interfacial, and amorphous phases. PBTBPP has a much higher T sub g than PBEPP, shows little evidence of crystallinity, and appears to be liquid crystalline both above and below T sub g.