Biodegradable aliphatic/aromatic copoly(ester-ether)s: the effect of poly(ethylene glycol) on physical properties and degradation behavior

A series of high molecular weight copolymers based on poly(L-lactic acid) (PLLA) as the biodegradable aliphatic segments, poly(butylene terephthalate) (PBT) as the rigid aromatic segments and hydrophilic poly(ethylene glycol) (PEG) as the soft segments were synthesized with the aim of developing novel polymer materials which could combine high physical properties with good biodegradability. Via direct melt polycondensation of terephthalic acid (TPA), 1,4-butanediol (BDO), poly(L-lactic acid) oligomer (OLLA) and PEG, biodegradable aliphatic/aromatic copoly(ester-ether)s, poly(butylene terephthalate-co-lactate-co-ethylene glycol) (PBTLG), were prepared. The effect of the introduction of PEG soft segments on the synthesis, mechanical properties and thermal stabilities as well as the degradation behaviors of the final copolymers was investigated. When the PEG units were incorporated into the polymer main-chains, the weight-average molecular weight of the copolymers increased from 53,700 g/mol to 177,000 g/mol and the tensile strength (σ) improved by nearly two times from 6.5 MPa to 12.8 MPa for PBTLG1000-0.5. The glass-transition temperature (T _g) gradually decreased from 26.9 °C down to −5.5 °C and a depression of melting temperature was observed with the increase of PEG content. According to the in vitro hydrolytic degradation observation, all of the copolymers underwent significant degradation in phosphate buffer solution at 37 °C and the water absorption as well as the degradation rate of PBTLGs displayed a strong dependency on the PEG content.