HEAT STABILITY OF SELECTED POLYPHOSPHAZENES

The mechanism of thermal degradation of poly{lcub}bis(trifluoroethoxy)phosphazene{rcub} (PBFP) and poly{lcub}bis(phenoxy)phosphazene{rcub} (PBPP) have been examined using dynamic and isothermal thermogravimetry. The thermal measurements were made in helium, using a Perkin-Elmer TGS-2. The dynamic measurements were made between 50(DEGREES) and 750(DEGREES)C at the heating rates of 2.5(DEGREES), 5(DEGREES), 10(DEGREES), 20(DEGREES), 40(DEGREES) and 80(DEGREES)C/min, and the data was analyzed using the method of (a) Flynn and Wall; (b) Reich and Stivala. The isothermal measurements were made at 325(DEGREES), 340(DEGREES), 355(DEGREES) and 370(DEGREES)C, and the data was analyzed by a procedure outlined by Madorsky. The polymers and their degraded residues were characterized by gel permeation chromatography, infrared spectroscopy and intrinsic viscosity. Some of the gaseous decomposition products were examined by mass spectroscopy. In PBFP, activation energy for degradation (E(,d)) was between 23.2 (isothermal) to 26.6 (dynamic) kcal/mole. The order of reaction (n), was 0.3 (+OR-) 0.1. Maxima in the isothermal rates of degradation occurred between 30 and 35% weight loss. Based upon experimental results the mode of initiation was deduced as occurring at the chain ends. A possible pathway for chain transfer has been proposed, based upon the degradation products observed.; In the case of PBPP, the dynamic thermogravimetry revealed two activation energies of 37 (+OR-) 1.5 and 26 (+OR-) 1.5 kcal/mole beyond 5% weight loss at all conversion levels, the differential weight loss was skewed and a 25% residue was present at 600(DEGREES)C. The residue from the isothermal measurements was between 31 and 35% and an activation energy of 32 kcal/mole was deduced. Difficulty was encountered when dissolving the degraded samples, and a depolymerization light crosslinking mechanism is proposed to explain it. One possible pathway for such a mechanism is suggested.; From a practical viewpoint, the relative thermal stability of nine poly(phosphazene) samples have been compared by dynamic thermogravimetry in nitrogen made at several heating rates. The data was analyzed using the method of Flynn and Wall. The samples varied in filler type (carbon black, silica, alumina trihydrate) and structure of the side groups (alkoxy, aryloxy and amino). Flame spread velocity and oxygen index measurements were made on five of these samples for evaluation of their fire potential hazard in practical situations.