Synthesis and characterization of biodegradable aliphatic copolyesters with poly(ethylene oxide) soft segments

A series of multiblock poly(ether-ester)s based on poly(butylene succinate) (PBS) as the hard segments and hydrophilic poly(ethylene oxide) (PEO) as the soft segments was synthesized with the aim of developing degradable polymers which could combine the mechanical properties of high performance elastomers with those of flexible plastics. The aliphatic poly(ether-ester)s were synthesized by the catalyzed two-step transesterification reaction of dimethyl succinate, 1,4-butanediol and α,ω-hydroxyl terminated poly(ethylene oxide) (PEO, = 1000 g/mol) in bulk. The content of soft PEO segments in the polymer chains was varied from about 10 to 50 mass%. The effect of the introduction of the soft PEO segments on the structure, thermal and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of these aliphatic segmented copolyesters were determined by ¹H NMR spectroscopy. The molecular weights of the polyesters were verified by gel permeation chromatography (GPC), as well as by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using differential scanning calorimetry (DSC). The degree of crystallinity was determined by means of DSC and wide-angle X-ray scattering. A depression of melting temperature and a reduction of crystallinity of the hard segments with increasing content of PEO segments were observed. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests in phosphate buffer solution with Candida rugosa lipase at 37 °C was compared with hydrolytic degradation in the buffer solution. The weight losses of the samples were in the range from 2 to 10 mass%. GPC analysis confirmed that there were significant changes in molecular weight of copolyesters with higher content of PEO segments, up to 40% of initial values. This leads to conclusion that degradation mechanism of the poly(ether-ester)s based on PEO segments occurs through bulk degradation in addition to surface erosion.