CHEMICAL-REACTIONS DURING THE THERMAL-PROCESSING OF BORAZENE POLYMERS

A class of borazene polymers was developed which consists of a two‐dimensional 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‐eched aluminum was examined by thermal decomposition mass spectroscopy (TDMS) and thermal gravimetric analysis (TGA), and the gas evolution chemistry was found to be essentially complete at temperatures 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, and HCl from decomposition of byproducts of the synthesis step. Since the formation of ordered crystalline h‐BN films requires heating to temperatures of the order of 1000°C, whereas the gas evolution chemistry is complete by roughly 400°C, it is concluded that gas evolution chemical processes are not rate limiting in BN ceramic production. Copyright © 1990, Wiley Blackwell. All rights reserved