Aromatic dinitriles cyclize to form aromatic polymers containing the s-triazine ring. In this paper, these polymers are compared thermally with each other and with aromatic melamine polymers prepared via the aromatic diamine and cyanuric chloride. One perfluoroaromatic melamine polymer was prepared and compared with the other two types of polymers. The polymers (triazines and melamine) in which biphenyl was the backbone were increasingly stable up to 1000°C. in nitrogen. The triazine polymers as a group were the most stable. The perfluoroaromatic polymer was the most stable melamine up to 500°C. in air but was very unstable above 700°C.