Novel biodegradable and biocompatible poly(is an element of-caprolactone)- graft- poly(ethylene oxide), PCL-g-PEO, copolymers consisting of biocompatible blocks have been synthesized by ring-opening copolymerization of is an element of-caprolactone (is an element of CL) and a poly(ethylene oxide) (PEO) macromonomer, i.e., PEO end-capped by an is an element of-caprolactone unit (gamma PEO.CL). The control is effective on the composition and length of both the hydrophobic polyester backbone and the hydrophilic PEO grafts. The reactivity ratios have been determined by monitoring the copolymer composition in relation to the comonomer conversion. The PCL-g-PEO copolymers have a tapered (gradient) rather than a random structure consistent with r(is an element of)CL = 3.95 and r(gamma)PEO.CL = 0.05. The amphiphilic graft copolymers display surfactant properties similar to those of PEO-b-PCL diblock copolymers of comparable composition and solubility, as supported by CHCl3/water interfacial tension measured by the pendant drop method.