The thermal properties of physical blends containing benzoxazine monomer and polycarbonate (PC) were studied by nonisothermal differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). The ring-opening reaction and subsequent polymerization reaction of the benzoxazine were inhibited significantly by the presence of polycarbonate. The glass-transition temperature of the resulting blends decreased as the concentration of polycarbonate increased and deviated markedly from the Fox equation. An earlier degradation event appeared in the blend with 11 and 33 wt % of PC. In addition, FTIR was used to study the extent of the polymerization reaction as well as the hydrogen-bonding behavior. Intermolecular hydrogen bonding between PC and cured polybenz-oxazine appeared after 1 h of isothermal curing at 180 degreesC and continued throughout the entire curing process.