2,2‐bis(3,4‐Dihydro‐3‐phenyl‐2H‐1,3‐benzoxazine)propane (BA‐a) is blended with three commercial organophosphorus compounds, bis(4‐ hydroxyphenyl)phenylphosphine oxide (BHPPO), diphenyl phosphorami‐date (DPPA), and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), at different loadings (1–10 wt%). Incorporation of all dopants results in a reduction in the initiation temperature for the curing mechanism (by some 30–60 K), but only the DOPO truly moves the curing into a lower temperature regime by decreasing the end temperature by 25 K (DPPA lowered this by 5 K). DPPA and DOPO are also shown to have a significant effect on the enthalpy of polymerization each decreasing the value by 50 J g−1. Differential scanning calorimetry rescan indicates all three additives have a positive impact on the glass transition temperature of poly(BA‐a) with increases of 9 K (BHPPO) and 14 K (DPPA, DOPO). Thermogravimetric analysis indicates that all additives have little effect on the magnitude of char formed (BHPPO and DPPA both increased the char yield by 3%, whereas DOPO reduces the nal char yield by 3%). However, importantly, the mechanism of thermal degradation for poly(BA‐a) differs for all three additives and is shown to change with increasing concentra‐ tion. DOPO has the greatest effect on promoting the formation of char at elevated temperatures.