The thermal properties of physical blends containing benzoxazine monomer and polycaprolactone (PCL) were monitored by DSC and Fourier transform infrared spectroscopy (FTIR). The ring-opening reaction and subsequent polymerization reaction of the benzoxazine were facilitated significantly by the presence of a PCL modifier. Hydrogen-bond formation between the hydroxyl groups of polybenzoxazine and the carbonyl groups of PCL was evident from the FTIR spectra. Only one glass-transition temperature (T-g) value was found in the composition range investigated, and the T-g value of the resulting blend appeared to be higher in the blend with a greater amount of PCL. (C) 2001 John Wiley & Sons, Inc.