A poly[(R,S)-3-hydroxybutyrate] macroinitiator (PHB-MI) was obtained through the condensation reaction of poly[(R,S)-3-hydroxybutyrate] (PHB) oligomers containing dihydroxyl end functionalities with 4,4'-azobis(4-cyanopentanoyl chloride). The PHB-MI obtained in this way had hydroxyl groups at two end of the polymer chain and an internal azo group. The synthesis of ABA-type PHB-b-PMMA block copolymers [where A is poly(methyl methacrylate) (PMMA) and B is PHB] via PHB-MI was accomplished in two steps. First, multiblock active copolymers with azo groups (PMMA-PHB-MI) were prepared through the redox free-radical polymerization of methyl methacrylate (MMA) with a PHB-MI/Ce(IV) redox system in aqueous nitric acid at 40degreesC. Second, PMMA-PHB-MI was used in the thermal polymerization of MMA at 60degreesC to obtain PHB-b-PMMA. When styrene (S) was used instead of MMA in the second step, ABCBA-type PMMA-b-PHB-b-PS multiblock copolymers [where C is polystyrene (PS)] were obtained. In addition, the direct thermal polymerization of the monomers (MMA or S) via PHB-MI provided AB-type diblocks copolymers with MMA and BCB-type triblock copolymers with S. The macroinitiators and block copolymers were characterized with ultraviolet-visible spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, cryoscopic measurements, and thermogravimetric analysis. The increases in the intrinsic viscosity and fractional precipitation confirmed that a block copolymer had been obtained. (C) 2004 Wiley Periodicals, Inc.