Synthesis and Hydrolytic Stability of Biodegradable Triblock Copolymers of L-Lactide and Lactones Using a Cleavable Initiator

초록

To enhance the hydrolytic degradability of poly(L-lactide) (PLA), a series of biodegradable triblock copolymers containing a cleavable moiety and hydrophilic midblock were synthesized via ring-opening polymerization (ROP). A cleavable trithiocarbonate-based initiator (BSCD) possessing terminal hydroxyl groups was first synthesized by the reaction of dibromobenzothiazole, carbon disulfide, and mercaptoethanol. Using BSCD, poly(delta-valerolactone) (PVL) or poly(epsilon-caprolactone) (PCL) midblock, which exhibits hydrophilicity and promotes water diffusion, was polymerized. This PVL or PCL midblock subsequently served as macroinitiators for the ROP of L-lactide, yielding triblock copolymers of PLA-b-PVL-b-PLA or PLA-b-PCL-b-PLA containing a cleavable trithiocarbonate moiety at the center. Introducing both hydrophilic midblock and trithiocarbonate linkages significantly improved the hydrolytic degradation of PLA, which is otherwise resistant under mild conditions. The cleavable moiety enabled aminolysis-triggered main chain scission, accelerating molecular weight reduction. After five weeks at 50 degrees C under aerobic conditions, the molar mass of PLA-b-PVL-b-PLA decreased by approximately 50%, confirming the enhanced degradability conferred by the incorporated cleavable structure and water-permeable midblock.

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