Polyisobutylene (PIB) possessing alkene end groups was ozonized. NMR spectroscopy showed that trioxolanes and tetroxolanes were the main products and that these products were relatively stable. Thermolysis of the ozonolysis products generated radicals, which were shown by ESR spin-trapping experiments to be alkyl and oxyalkyl species. Thermolysis in butyl propionate solution also generated radicals with structures consistent with those expected of species arising from hydrogen abstraction from solvent. Thermolysis in the presence of methyl methacrylate (MMA) or styrene (S) led to polymerization of both. Size exclusion chromatography (SEC) and gradient polymer elution chromatography (GPEC) were used to investigate the possibility that the newly formed polymer might be attached to PIB. In the case of MMA polymerizations, the final product was a blend of the two homopolymers: no evidence for block copolymers could be seen by SEC or GPEC. In contrast, both SEC and GPEC indicated that a large fraction of the newly formed polystyrene was attached to PIB, most probably in the form of P(IB-b-S) block copolymer.