Preparation, characterization, and polymerization of maleimidobenzoxazine monomers as a novel class of thermosetting resins

New series of benzoxazine-based monomers, namely maleimidobenzoxazines, were prepared with hydroxyphenylmaleimide, formalin, and various amines (e.g., aniline, allylamine, and aminophenyl propargyl ether). The structure of the novel monomers was confirmed by IR, H-1 NMR, and elemental analysis. The monomers were easily dissolved in many common organic solvents. Differential scanning calorimetry of the novel monomers showed exotherms at different temperature ranges that corresponded to the polymerization regime of benzoxazine and maleimide along with other functionalities such as allyl or propargyl, if any. IR was studied to follow the progress of the curing reaction of maleimidobenzoxazine after various thermal treatments. The thermal cure of the monomers at 250 degrees C afforded a novel network structure that combined polybenzoxazine and polymaleimide. The dynamic mechanical analyses showed that the storage moduli of the thermosets derived from maleimidobenzoxazine were kept constant up to high temperatures. The glass-transition temperatures were as high as 241-335 degrees C. Moreover, thermogravimetric analyses revealed that the thermosets did not show any weight loss up to about 350 degrees C, with char yields ranging from 62 to 70% at 800 degrees C. (c) 2006 Wiley Periodicals, Inc.