This article describes the synthesis and characterization of benzoxazine monomers prepared by reacting the mixture of amine (aniline [A], 3-chloroaniline [C], o-toluidine [T]) and phenol (bisphenol-A [B], phenol [P]) with formaldehyde [F]. The benzoxazine monomers prepared by reacting B and F with A, C, and T have been designated as BAF, BCF, and BTF, respectively. Structural characterization of benzoxazines was done using FTIR, H-1 NMR, and elemental analysis. The curing behavior of benzoxazine monomers was investigated by differential scanning calorimetry in the presence of diglycidyl ether of bisphenol-A (DGEBA). In all the samples, the molar ratio of benzoxazine monomer:DGEBA, was varied as 1 : 0, 3 : 1, 1 : 1, and 1 : 3. The peak exotherm temperature (T-p) was lowest in all the samples having molar ratio of 3 : I benzoxazine:DGEBA and highest in samples having molar ratio of I : 3. The heat of polymerization (Delta H) was found to be maximum during curing of mixture of DGEBA and benzoxazine monomer prepared from phenol, aniline and formaldehyde (PAF). Thermal stability of benzoxazines:DGEBA mixture cured isothermally was evaluated by recording thermogravimetric traces in nitrogen atmosphere. The char yield was highest for a mixture having benzoxazine : DGEBA in the ratio of 3 : 1. (c) 2007 Wiley Periodicals, Inc.