AbstractThe thermal stability of a variety of derivatives ofs‐triazine, benzene, and borazine was determined with an isoteniscope. For thes‐triazines the order of stability was found to be aryl triazines>aryl melamines and benzoguanamines>methyl melamines>higher alkyl melamines>aryl cyanurates and thiocyanurates (with the exception of fluoroalkyl cyanurates). The borazines were poorer than the melamines but better than the cyanurates. Several diand trifunctional linking groups were used to connect biphenyl groups which were known to be stable (from previous studies ofp‐quaterphenyl and polyphenyl ethers). The order of stability was found to be phosphate ≅ phosphine oxide ≅ ether>ester>amide>