A methodology for the synthesis of well-defined poly(ethylene oxide)block-poly(vinyl alcohol) (PEO-b-PVA) and PVA-b-PEO-b-PVA polymers was reported. Novel xanthate end-functionalized PEOs were synthesized by a series of end-group transformations. They were then used to mediate the reversible addition-fragmentation chain transfer polymerization of vinyl acetate to obtain well-defined poly(ethylene oxide)-b-poly(vinyl acetate) (PEO-b-PVAc) and PVAc-b-PEO-b-PVAc. When these block copolymers were directly hydrolyzed in methanol solution of sodium hydroxide, polymers with brown color were obtained, which was due to the formation of conjugated unsaturated aldehyde structures. To circumvent these side reactions, the xanthate groups were removed by adding a primary amine before hydrolysis and the products thus obtained were white powders. The polymers were characterized by gel permeation chromatography, H-1 NMR spectroscopy and FT-IR. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1901-1910, 2009