A novel triblock copolymer PSPHBPS based on the microbial polyester Poly[(R)-3-hydroxybutyrate)] (PHB) and poly(styrene) (PS) was prepared to be used as compatibilizer for the corresponding PHB/PS blends. It was prepared in a three-step procedure consisting of (i) transesterification reaction between ethylene glycol and a high-molecular-weight PHB, (ii) synthesis of bromo-terminated PHB macroinitiator, and (iii) atom transfer radical polymerization polymerization of styrene initiated by the PHB-based macroinitiator. Fourier transform infrared, gel permeation chromatography, 1H-, and 13C-NMR spectroscopies were used to determine the molecular structure and/or end-group functionalities at each step of the procedure. Although thermogravimetric analysis showed that the block copolymer underwent a stepwise thermal degradation and had better thermal stability than their respective homopolymers, differential scanning calorimetry displayed that the PHB block in the copolymer could not crystallize, and thus generating a total amorphous structure. Atomic force microscopy images indicated that the block copolymer was phase segregated in a well-defined morphological structure with nanodomain size of 40 nm. Contact angle measurements proved that the wettability properties of the block copolymer were in between those of the PHB and PS homopolymers. Blends analyzed for their morphology and thermal properties showed good miscibility and had well-defined morphological features. Polymer blends exhibited lower crystallinity and decreased stiffness which was proportional to the amount of compatibilizer content in the blends. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012