Diblock amphiphilic copolymers of PHB and monomethoxy poly(ethylene glycol) (mPEG) were synthesized in an one-step process by catalyzed transesterification in the melt [2]. The resulting diblock copolymers were self-assembled into sterically stabilized colloidal suspensions of PHB crystalline lamellae. Although microbial PHB in the diblock copolymer showed more crystalline and water insoluble, the architecture of the copolymers was not still suitable as drug carries because the crystalline PHB segments might cause the dense core and was difficult to encapsulate drugs. ABA-type triblock copolymers consisting of PEO and PHB were investigated by coupling two chains of PEO with a low-molecular-weight isotactic PHB chain in the middle (PEO–PHB–PEO) [3]. The crystallinity of the PHB block in the copolymers clearly increased compared with that of the pure PHB precursor, and their critical micelle concentrations (CMCs) were in the range of 13–1100 mg/L [4]. In fact, the CMC values of the PEO–PHB–PEO copolymers were too high, especially comparing with that of poly(ε-carprolactone) (PCL)–PEG and poly(l-lactide)(PLLA)–PEG (2.5–35 mg/L) [5] and [6]. The results implied that the PEO–PHB–PEO nanoparticles were very easy to dissociate upon dilution in the blood stream after intravenous injection, which was supported by the fact that all PEO–PHB–PEO copolymers were soluble in water [4].