The introduction of epoxy groups in the polymer backbone is one of the most promising methods of modifying polydienes. In this work the performance of the classical catalytic system VO(acac)(2)/tert-butylhydroperoxide was evaluated for the epoxidation of polydienes. The polymers investigated were a hydroxylated poly(butadiene), two polybutadienes with high and with low 1,4-content, a poly(isoprene), and a styrene-butadiene copolymer. The epoxidized polymers were characterized by IR, H-1 and C-13 NMR and GPC techniques. The vanadium system was active for the epoxidation reaction and the reactivity decreases in the order HTPB>PI>1,4-PB>1,2-PB-SBR. The occurrence of secondary reactions to low extension could be detected by the presence of hydroxyl, carbonyl and alcohol signals in the spectra of epoxidized polymers. Incomplete mass recovery (70-90%) was observed probably due to the chain degradation or modification of the polymer polarity. (C)2000 Elsevier Science B.V. All rights reserved.