Synthesis and thermotropic properties of new discotic 1,3,5-trisubstituted s-triazinetriones obtained by cyclotrimerization of isocyanates

Abstract

The synthesis of a number of s-triazine-2,4,6-triones (isocyanurates) by cyclotrimerization of 4-monoalkoxy-, 3,4-dialkoxy-, or 3,4,5-trialkoxyphenyl-, benzyl-, or styryl-isocyanates is reported. The thermal and phase behaviour of the novel compounds were investigated by optical polarized light microscopy and thermal analysis. No mesophase could be observed for any of the precursors except 4-decyloxybenzoic acid. Mesophases of the isocyanurates were observed only in the series containing 3,4-dialkoxyphenyl moieties. A vinylene group between the inner s-triazine ring and the outer phenylene rings gives low melting points and enantiotropic mesophases for C₈ and longer alkyl chains. The phenylisocyanurates may exhibit a monotropic mesophase and normally have the highest melting points of the three types, whereas a methylene spacer suppresses formation of a mesophase. According to the textures observed, the mesophases are hexagonal columnar. This will have to be confirmed by X-ray scattering techniques.