Strategy to prepare 4-hydroxylphenyl propargyl ether-based benzoxazine from bisphenol A

Abstract

4-Aminophenyl propargyl ether/phenol-based benzoxazine (P-appe) has been reported by many authors. However, to the best of our knowledge, its isomer: 4-hydroxylphenyl propargyl ether/aniline-based benzoxazine (HPPE-a) has never been prepared in the literature. The precursor for HPPE-a, the 4-hydroxylphenyl propargyl ether, is difficult to prepare from hydroquinone without tedious separation because the reactivity of the two hydroxyls in hydroquinone is the same. In this study, we report a straightforward strategy to prepare HPPE-a from bisphenol A by a four-step process including thermolysis, nucleophilic substitution, oxidation, and Mannich-type condensation. The structure was well characterized by NMR, IR, and high resolution mass spectra. Two exothermic peaks at 228 °C and 249 °C were observed in the DSC thermogram of HPPE-a. According to IR analysis, the first exotherm is related with the ring opening of the oxazine, and the second exotherm is related with Claisen rearrangement of propargyl ether. Since P-appe and HPPE-a are structural isomers, the structure–property relationship of these two benzoxazines was discussed. We found that the thermal properties of a thermoset of HPPE-a are slightly lower or comparable to those of a thermoset of P-appe, but much higher than that of phenol/aniline-based benzoxazine (P-a).