Three aromatic diamine-based benzoxazines were successfully prepared by a facile, clean, one-pot procedure from 1,4-phenylenediamine (1), 4,4'-diaminodiphenyl ether (2), and 4,4'-diaminodiphenyl methane (3), respectively. Their structures were confirmed by NMR spectra and single crystal diffractogram. The effect of the reactivity of diamines on the purity of the resultant benzoxazines was discussed. The resultant benzoxazines were applied as hardeners for cresol novolac epoxy (CNE). The processing window, the latent curing characteristic, and the miscibility of benzoxazine/CNE systems were discussed. Compared with diamines (1 and 3), (1 and 3)-based benzoxazines show latent curing characteristic as epoxy hardeners, and wide processing windows can be obtained. Compared with diamine (2) which is immiscible with CNE in the molten state, (2)-based benzoxazine shows good miscibility with CNE. Dynamic mechanical analysis shows the T(g)s of the benzoxazine/CNE thermosets are as high as 242-243 degrees C. Thermogravimetric analysis shows the outstanding thermal stability of the resultant thermosets. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2430-2437, 2010