a biodegradable copolymer with a core block comprising bioresorbable hydrophobic polyester segment and from 3 to 10 shell blocks comprising hydrophilic polyethylene glycol segment . the hydrophobic polyester segment and each of the hydrophilic polyethylene glycol segments are linked by a urethane linkage . a polymeric micelle composition containing the copolymer is also provided . the copolymer forms micelles when the concentration of the copolymer in a dispersing medium reaches or exceeds the critical micelle concentration . the micelles possess good drug and bioactive agent delivery characteristics and are suitable for use in drug delivery or cosmetic applications .