Block copolyesters based on poly(lactide) and aromatic-aliphatic polyesters of the AA/BB type and acid functionalized poly(lactide) and poly(ester-urethane)s therefrom

Aromatic-aliphatic poly[L-lactide-b-(ethyleneoxyethylene terephthalate-co-adipate)-b-L-lactide] triblock copolymers were synthesized and characterized. Hydroxy-telechelic poly(ethyleneoxyethylene terephthalate-co-adipate) (PEOETA) was first prepared via polycondensation and then utilized as an initiator for the ring opening polymerization (ROP) of L-lactide (LLA) in the presence of stannous octanoate (Sn(Oct) 2). Formation of the block copolymer was confirmed by 1H NMR spectroscopy, GPC, DSC and AFM. The polymerization rate induced by the PEOETA macroinitiator was comparable to that of a small molecule initiator. The mechanical and degradation properties failed to meet project objectives; therefore we focused more attention to the modification of alpha-hydroxy acid polymers for use in the creation of degradable polyurethanes.; Linear poly(D,L-lactide) containing a single pendant carboxylic acid group (BHMBA-PDLLA) was synthesized via ring opening polymerization (ROP) of D,L-lactide using 2,2-bis(hydroxymethyl) butyric acid (BHMBA) as an initiator. Characterization of the BHMBA-PDLLA using NMR spectroscopy and gel permeation chromatography confirmed the presence of the pendent carboxylic acid group and provided evidence of a linear architecture. Degradation studies were performed on BHMBA-PDLLA polyesters by immersion into aqueous buffered solution (7.4 pH) held at a constant temperature of 37°C. Complete degradation of the BHMBA-PDLLA occurred at times much earlier than those of the controls. These poly(alpha-hydroxy acid) polymers have shown promising degradation results when chain-extended using L-lysine diisocyanate methyl ester as the chain-extending agent.