Mechanism of Thermal Degradation of Some Polyphosphazenes

摘要

The mechanism of degradation of poly(bis(trifluoroethoxy)(phosphazene) (PBFP) and poly(bis(phenoxy)(phosphazene) (PBPP) have been examined using dynamic and isothermal thermogravimetry. The dynamic experiments were made between 50 deg and 750 deg C at several heating rates from 2.5 deg to 80 deg C/min. and the isothermal measurements were made at 325 deg, 340 deg, 355 deg and 370 deg C. The polymers and their degraded residues were characterized by gel permeation chromatography, infrared spectroscopy and intrinsic viscosity. In PBFP, the overall activation energy for degradation (Ed) was between 23.2 (isothermal) to 26.6 (dynamic) kcal/mole. The order of reaction was 0.3 + or - 0.1. Maxima in the rates of isothermal degradation occurred between 30 and 35% weight loss. Based upon experimental results, the mode of initiation in PBFB was deduced as occurring at the chain ends. Sample molecular weight dropped rapidly with degradation in harmony with a few random breaks occurring at weak points along the main chain after the degradation has been initiated at the chain ends. Literature results on the thermal degradation of PBFP in vacuum was shown to be consistent with a terminal initiation-chain transfer mechanism.