High temperature behavior of poly[bis(2,2,2-trifluoroethoxy)phosphazene]

Abstract

SUMMARY: Mesomorphic features of poly[bis(2,2,2-trifluoroethoxy)phosphazene] (PBFP) with high (L10 7 ) and low (L10 4 ) molecular weights have been investigated by X-ray diffraction techniques, differential scanning calorimetry optical and electron microscopy, and small-angle X-ray scattering. Characterization measurements were made from room temperature to L300 8C, which is well above T m , the designated melting temperature of PBFP. The wide angle X-ray scattering (WAXS) may be interpreted in support of some kind of "nano-scale order" persisting above the isotropization temperature, T m , of this polymer. There is other evidence to the contrary, namely the optical isotropicity between crossed-polars (depicts melting) and the absence of discrete small angle X-ray scattering (SAXS) under these same conditions. An attempt is made here to establish if these features above T m are related to molecular weight.

Kinetics of phase transitions and dielectric relaxations in poly-bis(trifluorethoxy- phosphazene) (PBFP)

“…The T(1)-transition is attributed to side group mobilisation as well as to the onset of thermally induced backbone motions [8]. Cooling from temperatures above T(1) results in highly crystalline specimens below T(1) [5,8].…”

“…Cooling from temperatures above T(1) results in highly crystalline specimens below T(1) [5,8]. Various aspects of these transitions have been reported in literature (a short overview is given in [8]).…”

“…In addition to the glass transition, PBFP shows a thermotropic transformation, T (1), between 330 -350 K and a melting temperature, T m , at about 500 K [5,6]. These values appear to depend on molecular mass as well as on thermal history [5,7,8].…”

“…Cooling from temperatures above T(1) results in highly crystalline specimens below T(1) [5,8]. Various aspects of these transitions have been reported in literature (a short overview is given in [8]). A high degree of crystallisation at temperatures below T(1) is indicated by the absence of a measurable effect in the specific heat at T g during differential scanning calorimetry DSC) [5].…”

“…A high degree of crystallisation at temperatures below T(1) is indicated by the absence of a measurable effect in the specific heat at T g during differential scanning calorimetry DSC) [5]. However, the degree of crystallization may depend on molecular mass and thermal history [8]. Further, freshly precipitated PBFP shows a different crystalline modification than after repeated heating and cooling: monoclinic vs. orthorhombic [4].…”