a method is described for a simple , fast and efficient synthesis of homopolymers and copolymers by the enzymatic ring opening polymerization of lactones and lactides . the enzyme used is an ion paired protease . the advantage of this enzymatic system is in using small amount of enzyme per monomer and lower reaction time . homopolymers and copolymers are synthesized with molecular weights between 1000 and 4600 daltons , and dispersity as low as 1 . 1 . the monomer conversion after 4 days , for reactions catalyzed by protease s , has reached 100 %. different initiators are used to control the rate and degree of polymerization . synthesis of block copolymers with defined block size and crystallinity are described in this invention . these biodegradable and bioerodable polyesters and copolyesters with controlled molecular weight , dispersity and crystallinity have applications in medical , drug , cosmetic and food industries .