The anionic polymerizations of 2-chloroethyl methacrylate (1), 2-bromoethyl methacrylate (2), and 2-iodoethyl methacrylate (3) were carried out in THF at -78 degreesC with 1,1-diphenyl-3-methylpentyllithium in the presence of LiCl. The polymerizations proceeded in a controlled manner to quantitatively afford polymers with predictable molecular weights and narrow molecular weight distributions. Under similar conditions, the anionic block copolymerizations by the sequential addition of methyl methacrylate (MMA) followed by 1, 2, and 3 generated the corresponding diblock copolymers with well-defined structures. On the other hand, in the block copolymerization by the reverse addition of monomer, a well-defined diblock copolymer, poly(1)-block-PMMA, could be synthesized only by the sequential addition of 1 followed by MMA, whereas the block copolymerizations using 2 and 3 were not successful because of instabilities of the propagating chain-end anions derived from 2 and 3. The side reactions which occurred during the polymerization were discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.