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 degrees C and characterized with spectral analysis. Upon photolysis around 300 mm, this monomer underwent dimerization via the [2 pi s+2 pi s] cycloaddition reaction. Photodimerization reactions were investigated with LTV and (1)H 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. (c) 2007 Wiley Periodicals, Inc.