The first step in the transformation of poly(butadienyl)lithium into a macromolecular atom transfer radical polyrnerization initiator or reversible addition-fragmentation chain transfer agent is the modification of the anionic chain end into a suitable leaving/reinitiating group. We have investigated three different modification reactions to obtain a styrenic end group at the chain end of poly(butadienyl)lithium. In all cases, we have looked at the influence of a Lewis base on the progress of the reaction. The first modification reaction with a-methylstyrene leads to partial functionalization and oligomerization. The second reaction with 1,2-diphenylethylenes, particularly trans-stilbene, results in monoaddition to the poly(butadienyl)lithium chain ends. Quantitative functionalization is not obtained, possibly because of a hydrogen abstraction reaction, which causes termination. In the third modification reaction, a small polystyrene block is successfully added to the chain ends, as shown by a detailed matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of the block copolymers. Nearly quantitative block copolymer formation is achieved, with an average styrene block size of four monomer units and a polydispersity index of 1.19 for the polystyrene block. (c) 2005 Wiley Periodicals, Inc.