Synthesis of a Bisbenzylideneacetone-Containing Benzoxazine and Its Photo- and Thermally Cured Thermoset

A bis­(4-hydroxybenzylidene)­acetone/aniline-based benzoxazine (<b>BHBA-a</b>) was prepared from a bisbenzylidene-containing bisphenol, bis­(4-hydroxybenzylidene)­acetone (<b>BHBA</b>), aniline, and paraformaldehyde through Mannich condensation in a cosolvent of toluene/ethanol (2:1, v/v). The structure of <b>BHBA-a</b> was successfully confirmed by Fourier transform infrared and ¹H and ¹³C NMR spectra. According to the differential scanning calorimetry (DSC) thermogram of <b>BHBA</b>, an immediate exothermic peak after the melting peak was observed, suggesting that <b>BHBA</b> is thermally active. NMR data of thermally treated <b>BHBA</b> confirm that the immediate exothermic peak after melting of <b>BHBA</b> in the DSC thermogram is resulted from the curing of a double bond. UV and ¹H NMR spectra of <b>BHBA-a</b> show that the bisbenzylideneacetone moiety underwent dimerization through the [2π + 2π] cycloaddition. Therefore, two procedures were applied to cure <b>BHBA-a</b>. The first one was thermal curing of the double bond of bisbenzylideneacetone and oxazine moieties. The second one was photocuring of the bisbenzylideneacetone moiety, followed by thermal curing of the oxazine moiety. The thermal properties of thermosets were evaluated based on these two procedures. Thermosets of <b>BHBA-a</b> exhibit <i>T</i>_g as high as 318 °C for curing procedure 1 and 342 °C for curing procedure 2. These values are much higher than that of a traditional bisphenol/aniline-based benzoxazine thermoset. We conclude that the thermal curing of the double bond of bisbenzylideneacetone and photodimerization of bisbenzylideneacetone contributes to the good thermal properties