Thermally curable benzoxazine monomer with a photodimerizable coumarin group

A new monomer, 4-methyl-9-p-tolyl-9,10-dihydrochromeno[8,7-e][1,3]oxazin- 2(8H)-one, possessing both benzoxazine and coumarin rings in its structure was synthesized by the reaction of 4-methyl-7-hydroxycoumarin, paraformaldehyde, and p-toluidine in methanol at 40°C and characterized with spectral analysis. Upon photolysis around 300 nm, this monomer underwent dimerization via the [2πs+2πs] cycloaddition reaction. Photodimerization reactions were investigated with UV and ¹H NMR spectroscopy measurements. The thermal ring-opening reaction of the benzoxazine ring was demonstrated with differential scanning calorimetry measurements. The thermal behavior of the cured product was also investigated with thermogravimetric analysis.