Abstract
This paper describes a novel synthetic strategy for the preparation of thiol end-functionalized poly(ethylene glycol) (PEG)-b-polyesters. Block copolymers containing an internal disulfide bond were prepared through the ring-opening polymerization of dl-lactide (LA) and e-caprolactone (CL) employing a PEG disulfide [(PEG-S)2] as the macroinitiator. This initiator was synthesized from α-tert-butanethio-ω-hydroxy-PEG (tBu-S-PEG) through the deprotection of tBu and the subsequent formation of a disulfide. The disulfide bond of the block copolymers was cleaved by reduction using tributylphosphine to generate block copolymers bearing a thiol at the PEG chain end. Thiolated PEG-b-PLA and PEG-b-PCL with number-average molecular weights (Mn) in the range of 3300−5800 and 3600−4600, respectively, were thereby obtained. The PLA and PCL contents could be varied according to the feed ratio and ranged between 20−47 and 15−30 mol %, respectively. Aqueous solutions of the disulfide block copolymers formed degradable gels...
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