Several dimeric and polymeric peroxycarbamates were synthesized using various aliphatic diisocyanates and hydroperoxides. The products were characterized by IR spectroscopy, molecular weight measurements, isocyanate and peroxide analyses. Thermal decomposition kinetics of these peroxycarbamates were studied in 1,4-dioxane or toluene solutions at 80, 90, and 100-degrees-C. All reactions were found to proceed according to a first-order kinetics with activation energies in the range of 126-144 kJ/mol, depending on the structure of the peroxycarbamate. One of the polymeric products was used to initiate methyl methacrylate polymerization at 80-degrees-C in bulk. The initiating activity of this peroxycarbamate was found to be better than that of some hydroperoxides.