Microwave (MW)-assisted ring-opening polymerization (ROP) provides a rapid and straightforward method for engineering a wide array of well-defined poly(3-hydroxyalkanoate)-b-poly(D,L-lactide) (PHA-b-PLA) diblock copolymers. On MW irradiation, the bulk ROP of D,L-lactide (LA) could be efficiently triggered by a series of monohydroxylated PHA-based macroinitiators previously produced via acid-catalyzed methanolysis of corresponding native PHAs, thus affording diblock copolyesters with tunable compositions. The dependence of LA polymerization on temperature, macroinitiator structure, irradiation time, and [LA]0/[PHA]0 molar ratio was carefully investigated. It turned out that initiator efficiency values close to 1 associated with conversions ranging from 50 to 85% were obtained only after 5 min at 115 degrees C. A kinetic investigation of the MW-assisted ROP of LA gave evidence of its living/controlled character under the experimental conditions selected. Structural analyses and thermal properties of biodegradable diblock copolyesters were also performed. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012