Mechanistic Investigation of Ring-Opening Polymerization of Polycaprolactone Using Tin(II) Catalysts: Ligand Effects and Biomedical Applications

This research explores the mechanistic aspects of ring-opening polymerization (ROP) of ε-caprolactone (CL) to produce polycaprolactone (PCL), a biodegradable polymer widely used in biomedical applications. The study investigates how light exposure and catalyst concentration influence polymerization efficiency, using tin(II) 2-ethylhexanoate [Sn(Oct)₂] as the catalyst in a non-polar toluene solvent at 90 °C. Reactions were conducted under either ambient light or black light bulb (BLB) illumination, with monomer-to-catalyst ratios of 1:1 and 200:1. Proton nuclear magnetic resonance (¹H NMR) spectroscopy was used to analyze conversion efficiency by tracking the disappearance of monomer signals and appearance of characteristic PCL peaks. Results revealed that near-complete conversion was achieved after 22 hours under both lighting conditions, with little difference observed between BLB and ambient light. However, reactions at shorter time points (5–10 hours) showed incomplete conversion, suggesting that time is a significant factor in achieving high yields. Catalyst concentration also played a major role; reactions with a 1:1 monomer-to-catalyst ratio reached completion more efficiently than those at 200:1. These findings demonstrate that Sn(Oct)₂ is an effective ROP catalyst across a range of light exposures and concentrations, with catalyst loading and reaction duration being the most critical factors. This work contributes to the growing body of knowledge on biodegradable polymer synthesis, providing insights that can improve the scalability and consistency of PCL production for biomedical applications, where precise control of degradation rate and polymer characteristics is essential.