It is confirmed that the major products of ozonolysis of tetramethylethene (TME) in butyl acetate at temperatures between −60 and 20°C are the cyclic peroxides, acetone diperoxide and acetone triperoxide plus, at low temperatures, species which may be open-chain oligoperoxides. Solutions of ozonized TME are able to initiate polymerizations of methyl methacrylate at temperatures above 60°C. ESR spectroscopy has shown that acetone diperoxide does not generate significant concentrations of radicals below 140°C, so that the chief initiating species below this temperature must be acetone triperoxide and the oligoperoxides. Despite the fact that these species have different structures, indicated by their differing retention times in GC and also their different mass spectra, they behave kinetically as one species, i.e. conversions to polymer after polymerization times of 1 h in the presence of ozonized TME are identical regardless of ozonolysis temperature.