In accordance with various embodiments, there is a method of making a polyester. The method can include providing a monomer solution, the monomer solution including one or more cyclic esters in a concentration ranging from about 1 to about 100% and one or more solvents in a concentration ranging from about 99% to about 0%. The method of making a polyester can also include providing a packed-bed reactor including one or more immobilized enzymes, wherein the packed-bed reactor has an inlet and an outlet. The method can further include circulating the monomer solution through the packed-bed reactor to generate a solution enriched with polyester, such that the one or more immobilized enzymes convert the one or more cyclic esters to polyester in the packed-bed reactor during circulation and collecting the solution enriched with polyester exiting through the outlet.