Synthesis and characterization of biodegradable triblock copolymers based on bacterial poly[(R)-3-hydroxybutyrate] by atom transfer radical polymerization

Biodegradable poly(tert-butyl acrylate)-poly[(R)-3-hydroxybutyrate]-poly (tert-butyl acrylate) triblock copolymers based on bacterial poly[(R)-3-hydroxybutyrate] (PHB) were synthesized by atom transfer radical polymerization. The chain architectures of the triblock copolymers were confirmed by H-1 NMR and C-13 NMR spectra. Gel permeation chromatography analysis was used to estimate the molecular weight characteristics and lengths of the PHB and poly(tert-butyl acrylate) blocks of the copolymers. The thermal properties of the copolymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA showed that the triblock copolymers underwent stepwise thermal degradation and had better thermal stability than their respective homopolymers, whereas DSC analyses showed that a microphase-separation structure was formed only in the triblock copolymers with the longer PHB block. As a similar result, from wide-angle X-ray diffraction experimentation, the crystalline phase of PHB could not be seen evidently in the triblock copolymers with the shorter PHB block. The enzymatic hydrolysis of the copolymer films was carried at 37 degrees C and pH 7.4 in a potassium phosphate buffer with an extracellular PHB depolymerase from Penicillum sp. The biodegradability of the triblock copolymers increased with an increase in the PHB block content. (c) 2005 Wiley Periodicals, Inc.