A novel two-step successive route to well-defined water-soluble poly(2,3-dihydroxypropyl methacrylate) [poly(DHPMA)] and the amphiphilic block;copolymers of DHPMA with styrene (St) or methyl methacrylate (MMA) was developed by combining the living anionic polymerization method with an osmylation reaction. Homopolymers of allyl methacrylate (AMA) with various molecular weights (M-n = 5900 - 170 000) and narrow molecular weight distributions (MWD; M-w/M-n = 1.06-1.16) were first prepared by the anionic polymerization of AMA using 1,1-diphenylhexyllithium (DPHL) as the initiator, in THF, in the presence of LiCl ([LiCl]/[DPHL](0) = 3), at -70 degrees C. Under similar conditions, the anionic block copolymerization of AMA with MMA generated well-defined di- anti triblock copolymers with controlled molecular weights and compositions as well as narrow MWDs (M-w/M-n = 1.05 - 1.16). Further, block copolymers of St and AMA with various compositions were prepared by performing the anionic block copolymerization of AMA from a 1,1-diphenylethylene-capped anionic living poly(St). In both the homopolymerization of AMA and its block copolymerization with MMA or St, its allyl side group remained unreacted. Without the (co)polymer separation from the (co)polymerization solution, the allyl groups of the (co)polymer were directly reacted with an excess of N-methylmorpholine N-oxide (NMO), in the presence of a small amount of osmium tetroxide as catalyst, at room temperature. This osmylation procedure changed the poly(AMA) component to poly(DHPMA). During this process, no cross-linking or polymer chain damage occurred, and well-defined water-soluble poly(DHPMA) and amphiphilic block copolymers were obtained. The molecular weight, molecular architecture, and the copolymer composition affect the hydrophilicities of the osmylated (co)polymers, and all these factors can be accurately controlled during the (co)polymerization step.