Chemical Reactions During the Thermal Processing of Borazene Polymers

Abstract

ABSTRACTA class of borazene polymers has been developed which consist of a twodimensional array of six-membered borazene rings with the borons of adjacent borazene rings separated by -NH- groups. Pyrolysis of these polymers above ≈1000 C leads to crystalline graphite-like boron nitride (h-BN). The thermal chemistry of thin films of one polymer deposited on KOH etched Al has been examined by thermal decomposition mass spectroscopy (TDMS) and thermal gravimetric analysis (TGA), and the gas evolution chemistry is found to be essentially complete by temperatures of less than 400 C. All products desorb with the same temperature profile and the major desorbing species are NH3 and N2 consistent with a loss of excess nitrogen and hydrogen in the polymer, ang HCI from decomposition of by-products of the synthesis step. Isotope labeling shows that complete exchange occurs below 400 C between the ring and amino bridge nitrogens. Since the formation of ordered crystalline h-BN films requires heating to temperatures of the order of 1000 C, whereas the gas evolution and ring opening chemistry is complete by roughly 400 C, it is concluded that gas evolution chemical Processes are not rate limiting in BN ceramic production.