Synthesis and properties of A-B-A block copoly(ester-ethers) comprising poly(L-lactide) (A) and poly(oxypropylene-co-oxyethylene) (B) with different molecular weights

An A-B-A triblock copoly(ester-ether) comprising poly(L-lactide) (A) and poly(oxyethylene-co-oxypropylene) (B) was prepared by copolymerization of L-lactide and a commercially available telechelic copolyether, Pluronic(R) (PN), with different molecular weights by the catalysis of tin(II) octanoate. The low molecular weight PN gave the copolymers having a low or medium molecular weight and a unit composition slightly different from the feed ratio. With PN whose molecular weight was around 10000, high molecular weight copolymers were obtained in high yield. For the PN with molecular weight of 8400, the block copolymerization was examined at different feed ratios, in which the molecular weight and the unit composition were successfully controlled by changing the L-lactide/PN ratio in feed. The copolymer containing 10 wt% of this PN was melt-spun into a filament, which was drawn to various draw ratios at 40 and 60 degrees C. The tensile modulus and strength of the filament increased with the draw ratio increasing at 60 degrees C, while at 40 OC they reached a plateau above the draw ratio of 5.0. It was found that the copolymer filaments showed an improved flexibility due to the incorporation of the soft PN segments. The in vitro hydrolysis test of the drawn filaments showed that the block copolymer has much higher degradability than the homo poly-L-lactide.