4-Acetyl phenyl methacrylate containing a polymerizable vinyl group was prepared by reacting 4-hydroxyacetophenone with methacryloyl chloride in the presence of triethylamine in methyl ethyl ketone. The vinyl monomer was characterized by Fourier transform infrared spectra. The polyurethanes obtained from castor oil, tolune-2-4-diisocyanate, and hexamethylene diisocyanate, with a varying NCO/OH ratio, were reacted with the new vinyl monomer 4-acetyl phenyl methacrylate to give interpenetrating polymer networks using ethylene glycol dimethacrylate as a cross-linker and benzoyl peroxide as initiator. The resulting interpenetrating networks were characterized for thermal behavior, and kinetic parameters were evaluated.