2-Hydroxy-4-methacryloyloxy acetophenone, a vinyl monomer, was prepared by reacting 2,4-dihydroxy acetophenone with methacryloyl chloride in presence of triethylamine in methyl ethyl ketone. The vinyl monomer was characterized by Fourier transform infrared spectra and Proton magnetic resonance spectra to confirm the various functional groups in the monomer. The liquid prepolyurethanes obtained from castor oil, toluene-2,4-diisocyanate, and hexamethylene diisocyanate, varying the NCO/OH ratio, were interpenetrated with the above vinyl monomer containing ethylene glycol dimethacrylate, using radical polymerization initiated by benzoyl peroxide. The interpenetrating polymer networks were obtained as transparent tough films by transfer moulding. They were characterized for thermal behavior with evaluation of kinetic parameters. From the kinetic data, it is clear that the degradation process of the interpenetrating networks is slower in the temperature range of 270-390 degrees C and faster in the range of 390-510 degrees C. Thermal stability also varies with the change in diisocyanates. The morphology was examined by scanning electron microscopy (SEM). The resulting two-phase morphology was found to be sensitive to change in monomer concentration. (C) 2000 John Wiley & Sons, Inc.