A trifunctional benzoxazine, 1,3,5-tris(3-phenyl-3,4-dihydro-2H-benzo[1,3] oxazin-6-yl)benzene (T-Bz) was synthesized and in an effort to reduce its curing temperature (curing maxima at 238 degrees C), it was mixed with various phenolic nucleophiles such as phenol (PH), p-methoxy phenol (MPH), 2-methyl resorcinol (MR), hydroquinone (HQ), pyrogallol (PG), 2-naphthol (NPH), 2,7-dihydroxy naphthalene (DHN), and 1,1'-bi-2-naphthol (BINOL). The influence of these phenolic nucleophiles on ring-opening polymerization temperature of T-Bz was examined by DSC and FTIR analysis. T-Bz undergoes a complete ring-opening addition reaction in the presence of bi-and trifunctional phenolic nucleophiles (MR/HQ/PG/DHN) at 140 degrees C (heated for 3 h) and forms a networked polybenzoxazine (NPBz). The NPBzs showed a high thermal stability with T-d20 of 350-465 degrees C and char yield of 67-78% at 500 degrees C; however, a diminutive weight loss (6.9-9.8%) was observed at 150-250 degrees C (T-d5: 215-235 degrees C) due to degradation of phenolic end groups. This article also gives an insight on how the traces of phenolic impurities can alter the thermal properties of pure benzoxazine monomer as well as its corresponding polymer. (C) 2016 Wiley Periodicals, Inc.