Water soluble biodegradable polymers were prepared by an organoacid catalyzed ring opening polymerization (ROP) of a cyclic carbonate monomer bearing an active ester side chain. The initial polymer comprising an active ester side chain was treated with an amino-alcohol, which transformed the active ester groups to N-substituted amide groups bearing mono-hydroxy alkyl groups and/or dihydroxy alkyl groups, thereby forming the water soluble polymers. The water-soluble polymers are non-toxic and exhibit stealth properties in buffered serum solution.