The synthetic parameters for the chemoenzymatic cascade synthesis of block copolymers combining enzymatic ring-opening polymerization (EROP) and atom transfer radical polymerization (ATRP) in one pot were investigated. A detailed analysis of the mutual interactions between the single reaction components revealed that the ATRP catalyst system could have a significant inhibiting effect on the enzyme activity. The inhibition of the enzyme was less pronounced in the presence of multivalent ligands such as dinonyl bipyridine, which thus could be used in this reaction as an ATRP catalyst. Moreover, the choice of the ATRP monomer was investigated. Methyl methacrylate interfered with EROP by transesterification, whereas t-butyl methacrylate was inert. Block copolymers were successfully synthesized with this cascade approach by the activation of ATRP after EROP by the addition of the ATRP catalyst and, with lower block copolymer yields, by the mixing of all the components before the copolymerization. A detailed kinetic analysis of the reactions and the structure of the block copolymers showed that the first procedure proceeded smoothly to high block copolymer yields, whereas in the latter a noteworthy amount of the poly(t-butyl methacrylate) homopolymer was detected. (c) 2006 Wiley Periodicals, Inc.