The oxidative copolymerization of indene with styrene, alpha-methylstyrene, and alpha-phenylstyrene is investigated. Copolyperoxides of different compositions have been synthesized by the free-radical-initiated oxidative copolymerization of indene with vinyl monomers. The compositions of the copolyperoxides obtained from the H-1 and C-13 NMR spectra have been used to determine the reactivity ratios of the monomers. The reactivity ratios indicate that indene forms an ideal copolyperoxide with styrene and alpha-methylstyrene and alternating copolyperoxides with alpha-phenylstyrene. Thermal degradation studies via differential scanning calorimetry and electron-impact mass spectroscopy support the alternating peroxide units in the copolyperoxide chain. The activation energy for thermal degradation suggests that the degradation is dependent on the dissociation of the peroxide (-O-O-) bonds in the backbone of the copolyperoxide chain. Their flexibility has been examined in terms of the glass-transition temperature.