Tuning the Degradability Profiles of Polyesters with Indium-Catalyzed Incorporation of Poly(ε-thiocaprolactone) Blocks

There are no examples of high molecular weight (>100 000 g/mol) poly­(ε-thiocaprolactone) (PtCL), and the mechanism of ε-thiocaprolactone (tCL) polymerization with organometallic complexes has not been investigated. In this work, we demonstrate the synthesis of the highest reported molecular weight PtCL (Mn = 109 000 g/mol) by using a cationic indium thiolate catalyst formed in situ via the addition of benzyl mercaptan. The mechanism of the polymerization is thoroughly investigated and the reaction coordinate is elucidated via computational calculations; the polymerization propagates through a coordination–insertion mechanism. If the PtCL is not isolated during the polymerization, the resulting indium-PtCL macromolecule can be used as an initiator to form copolymers with poly­(lactide) (PLA) and poly­(ε-caprolactone) (PCL). Incorporating 10% PtCL in these polymers alters their degradation behavior: the hydrolytic degradation period of PLA is reduced by nearly half, while PCL becomes more resistant to hydrolysis.