INFLUENCE OF DIFFERENT ORGANIC SIDE GROUPS ON THE THERMAL-BEHAVIOR OF POLYPHOSPHAZENES - RANDOM CHAIN CLEAVAGE, DEPOLYMERIZATION, AND PYROLYTIC CROSS-LINKING

The thermal behavior of several polyphosphazenes was examined. The polymers were studied by thermogravimetric analysis between 50 and 1000 °C, by bulk pyrolysis in a tube furnace over the same temperature range, and by thermolysis in a closed system. The volatile products were analyzed by a combination of 31P NMR spectroscopy, vapor-phase chromatography, and mass spectrometry. Three distinct processes were identified: (1) random chain cleavage of the phosphazene backbone, (2) depolymerization to form small molecule cyclic phosphazenes, and (3) cross-linking reactions to form a network structure. During pyrolysis [NP(OCH2CF3)2]n underwent random chain cleavage and depolymerization followed by volatilization of the small-molecule cyclic products. Species [NP(CH3)2]n and [NP(CH3)(C6H5)]n depolymerized to cyclic oligomers, which then volatilized. The aryloxy-substituted phosphazenes [NP(OC6H5)2]n and [NP(OC6H4CH3-p)2]n underwent random chain cleavage, depolymerization to cyclic oligomers, and cross-linking of these cyclic species. High-temperature pyrolysis of [NP(NHC3H7-n)2]n and other poly-(aminophosphazenes) and the transannular metallocene polymers [NP(OCH2CF3)4(η-C5H4)2Fe]n and [NP(OCH2CF3)4(η-C5H4)2Ru]n resulted exclusively in cross-linking reactions. Possible reaction mechanisms are considered. © 1990, American Chemical Society. All rights reserved.