Synthesis and characterization of diblock, triblock, and multiblock copolymers containing poly(3‐hydroxy butyrate) units

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 40°C. Second, PMMA‐PHB‐MI was used in the thermal polymerization of MMA at 60°C 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. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1789–1796, 2004