| Abstract: | Thermotropic aromatic polyesters based on 2,6-naphthalenedicarboxylic acid and 4,4′-dihydroxy-1,6-diphenoxyhexane 1a and -decane 1b have been synthesized by solution polymerization. The solid-state structures of these polyesters have been examined by high-resolution solid-state CP/MAS (cross polarization/magic angle spinning) and solution 13C-NMR. For precipitated original samples, alkylene spacers were generally in the all-trans form in the solid state. For once-melted samples, torsional gauche conformations were introduced to the spacers. The mesophase of the polyesters was identified as nematic. The temperature ranges of the nematic state of 1a and 1b were much wider than those of analogous polymers 2a and 2b based on terephthalic acid. For these polyesters, the substitution of the 2,6-naphthalene ring for the benzene ring induced no appreciable change in the conformation of the diphenoxy alkylene units in the solid state and on the melting points. Thermotropic ester model compounds, i.e., bis(4-butoxyphenyl) 2,6-naphthalate 3a and bis(4-butylphenyl) 2,6-naphthalate 3b have been prepared and characterized by both solid-state and solution NMR, which helped the interpretation of the solid-state structures of the polyesters. These spectra were compared with those of terephthalate-based related compounds 4a and 4b . The solid-state spectra suggest that the butoxyphenyl group of 3a and the butylphenyl group of 3b formed almost the same conformations as those of 4a and 4b , respectively. |
