Characterization of biodegradable poly(3-hydroxybutyrate-co-butyleneadipate) copolymers obtained from their homopolymers by microwave-assisted transesterification

Copolymers containing (R)-3-hydroxybutyric acid (HB), 1,4-butanediol (B), and adipic acid (A) weresynthesized by microwave-assisted transesterification of biodegradable poly(R-3-hydroxybutyrate)(PHB) and poly(1,4-butyleneadipate) (PBA) in solution at different reaction times, composition of thestarting mixture, and amount of 4-toluenesulfonic acid, used as a catalyst. The copolyesters werecharacterized with regard to their molecular weights, thermal properties, molar composition, andaverage block length of repeating units by gel permeation chromatography (GPC), differential scanningcalorimetry (DSC), wide angle X-ray diffraction (WAXS), 1H-NMR, and 13C-NMR, respectively. Randomand microblock copolymers could be obtained depending on experimental conditions, with weightaverage molecular weight of up to 17,000. The glass transition temperature (Tg) of all samples lay in therange between the Tgs of PBA and PHB, while their structure varied from partially crystalline to totallyamorphous. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra ofcopolymers allowed us to ascertain that they were hydroxyl and carboxyl chain-end terminated.