Biodegradable Poly(ester-urethane)s based on Poly[(R)-3-hydroxybutyrate] and Poly(e-caprolactone) blocks: thermal, mechanical and biodegradation behaviour

Gamal R. Saad, Tamer M. Khalil and Magdy W. Sabaa

Department of Chemistry, Faculty of Science, University of Cairo, Giza, P.O. 12613, Egypt

Abstract

a-w-Dihydroxy-terminated poly[(R)-3-hydroxybutyrate] (PHB-diol) (Mn ~ 4800) was synthesized by transesterification of the corresponding PHB homopolymer with 1,4-butanediol in presence of p-toluenesulfonic acid. It was subsequently combined with poly(e-caprolactone)-diols (PCL-diols) (Mn ~ 1260 and 2200) acting as soft segment via 1,6-hexamethylene diisocyanate to high molecular weight poly(ester-urethane)s. The content of PHB acting as hard segments systematically varied from ~20 to 60 wt.%. The synthesized materials were characterized by FTIR, 1H-NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile properties. In the case of segmented poly(ester-urethane)s, those samples obtained from PCL (Mn ~ 1260) showed an increase in Tgs with increasing PHB content, indicating some extent of PCL/PHB segment phase mixing. All of the investigated copolymers were semicrystalline with Tm of PCL phase varying from 39-47C and PHB phase varying from 141-150C. The TGA analysis of the investigated copolymers showed three distinct weight loss steps assigned to the thermal degradation of PHB, PCL and urethane linkage with increasing temperature, respectively. As for mechanical tensile, it was found that the ultimate strength and elongation at the breakpoint decrease with increasing PHB content. The biodegradability was studied in active soil. The results showed that the biodegradation rate of the investigated copolymers increases with increasing PHB content.