Several dimeric peroxycarbarnates (PCs) have been synthesized by using cycloaliphatic and aromatic diisocyanates with mono- and di-hydroperoxides. The reactions were carried out under suitable conditions either in the presence of T-12 (dibutyltin dilaurate) as catalyst or in the absence of this catalyst. The products were characterized by IR-spectra and molecular weight measurements from isocyanate and peroxygen analyses. Thermal decomposition kinetics of these PCs were studied in THF solution at 80, 90 and 100 degreesC the reactions were found to be first-order and decomposition rate constants (k(d)) were found. Activation energies and frequency factors for the decomposition were calculated. Activation energies were found to be in the range 67-121 kJ mol(-1) and frequency factors were of the order of 10(11)-10(15) s(-1) depending on the structure of the PC. The results for the PCs agree well with literature values. (C) 2002 Elsevier Science Ltd. All rights reserved.