Copolyperoxides of different compositions of indene with vinyl acetate and isopropenyl acetate were synthesized by the free radical-initiated oxidative copolymerization. The compositions of copolyperoxides obtained from H-1- and C-13-NMR spectra have been used to determine the reactivity ratio of the monomers. The reactivity ratios reveal that the copolyperoxides contain a larger proportion of the indene units in random placement. The NMR studies further suggest irregularities in the copolyperoxide chain possibly due to the cleavage reactions of the propagating peroxide radical. The thermal analysis by differential scanning calorimetry (DSC) supports the alternating peroxide units in the copolymer chain. The activation energy for the thermal degradation suggests that the degradation is dependent on the dissociation of the peroxide (-O-O-) bonds in the copolyperoxide chain.