Chiang Mai Journal of Science

     Tri-n-butyltin(IV) n-butoxide (nBu₃SnOnBu) was successfully synthesized and utilized as a stable and homogeneous initiator for the small-scale synthesis of biodegradable polymers in our laboratory. From our previous works, the initiating performance of nBu₃SnOnBu in the ring-opening polymerization (ROP) of cyclic ester monomers was completely investigated by differential scanning calorimetry (DSC). It was found that nBu₃SnOnBu acted as the slow initiator in the ROP of ε-caprolactone (ε-CL) due to its high steric hindrance around the active center. Moreover, it could be used in the stereoselective ROP of racemic-lactide (rac-LA). The synthesized nBu₃SnOnBu showed higher stereoselectivity than the conventional tin(II) octoate (Sn(Oct)₂) system. In this present work, the effectiveness of nBu₃SnOnBu in scaled-up (250 g) of the synthesis of poly(ε-caprolactone) (PCL) was further investigated comparing to small-scale polymerization (4 g). Furthermore, the catalytic performance of this nBu₃SnOnBu in the transesterification of high molecular weight poly(L-lactic acid) (PLA) was also investigated for the first time. The transesterification of PLA with 0.05 M and 0.10 M of soluble nBu3SnOnBu catalyst in CHCl₃ was successfully investigated by the gel permeation chromatography (GPC) technique. It was found that the molecular weight of PLA dramatically decreased with increasing time and nBu₃SnOnBu concentration. From the kinetics study, nBu₃SnOnBu acted as a highly active transesterification catalyst for PLA. From a mechanistic study, the transesterification mechanism of PLA with nBu₃SnOnBu catalyst was proposed through intramolecular transesterification.