The sterically hindered, 1,1-disubstituted monomers di-n-butyl itaconate (DBI), dicyclobexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition-fragmentation chain transfer (RAFT) free-radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2-eyanoprop-2-yl dithiobenzoate, 4-cyanopentanoic acid dithiobenzoate, and S-methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60 degrees C yielding polymers ranging in their number-average molecular weight from 4500 to 60,000 g mol(-1). The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free-radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N ',N '',N ''-pentamethyldiethylenetriamine/cyclohexanone system at 60 degrees C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15-3.35). To assess the cause of this broadness, chain-transfer-to-monomer constants for DMI, DBI, and DCHI were determined (1.4 x 10(-3), 1.3 X 10(-3), and 1.0 x 10(-3), respectively) at 60 degrees C. Simulations carried out with the PRE-DICI program package suggested that chain transfer to monomer contributed to the broadening process. In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions. (c) 2006 Wiley Periodicals, Inc.