Controlled radical polymerization of N-vinylcaprolactam (NVCL) via reversible addition-fragmentation chain transfer (RAFT) polymerization or macromolecular design via the interchange of xanthate (MADIX) was described, employing 2-diphenylthiocarbamoylsulfanyl-2-methyl-propionic acid (CTA1), ((O-ethylxanthyl)methyl)benzene (CTA2) and (1-(O-ethylxanthyl)ethyl)benzene (CTA3) as chain transfer agents (CTA). It was found that all the CTAs led to controlled radical polymerization of NVCL, with the molecular weight increased along with the conversion of monomer and a relatively narrow molecular weight distribution could be obtained, as determined with matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) and gel permeation chromatography (GPC), the polydispersity indices, as determined by MALDI-TOF, were typically on the order of 1.24, but the polymerization did not proceed in a strictly living manner. The chain transfer ability of these CTAs was in the following order: CTA1 approximate to CTA2 < CTA3. MALTI-TOF measurement showed that the major population of polymer retained the chain-end functional group, but minor population deactivated by radical coupling. In preparation of the block copolymer of NVCL and vinyl acetate (VAc) by sequential polymerization, the sequence of monomer addition was important. Using VAc as the first monomer could lead to a block copolymer presenting a unimodal GPC trace and a narrow PDI index, and if NVCL was used as the first monomer, the polymerization was less well controlled. (C) 2008 Wiley Periodicals, Inc.