A monomer with two 4-(trifluoromethyl)-5-fluoro-substituted thiazole rings was prepared from terephthalic acid dithioamide and hexafluoroacetone. This monomer was converted to poly(aryl ether thiazole)s by nucleophilic displacement of the fluorine atoms on the thiazole rings with bis(phenol)s or silylated bis(phenol)s. The products obtained by the silyl method exhibit molar masses up to (M) over bar(w) = 78 500 g . mol(-1). Compared to analogous polymers with oxazole rings in place of the thiazole rings, the thiazole polymers had higher glass transition temperatures and decreased solubilities. This is attributed to the different geometries of the thiazole and oxazole rings. In addition, the decomposition temperatures of the thiazole polymers were at least 100 deg higher than those of the oxazole polymers. This effect is caused by the more pronounced aromatic character of the sulfur heteroaromatic rings as compared to the oxygen-based systems.