Ring opening polymerization of ε-caprolactone through water

Ring opening polymerization (ROP) is commonly used to synthesize biodegradable polymers such as polycaprolactone (PCL). These reactions typically demand anhydrous reagents and inert atmosphere, only attainable through the use of complex setups including glove boxes and Schlenk lines. Because of these practical limitations, ROP is typically inaccessible to the non-expert. Herein, we have developed two techniques for limited ROP of epsilon-caprolactone (CL) without previous drying of reagents by simply conducting the reaction in a laboratory oven. In the first method, a vacuum oven was used to evaporate water from a traditional ROP reaction with stannous octoate (Sn(Oct)(2)) as the catalyst. In the second method, we 'polymerize through' water using titanium isopropoxide (TTIP) to simultaneously quench residual water and catalyze ROP. Using these two methods, we achieved variable chain length (degree of polymerization (DP) 25-500) and molecular weight distribution (D = 1.3-1.5) of PCL. We found that ROP with TTIP works better for higher molecular weights up to DP 500 than Sn(Oct)(2) under vacuum. Moreover, we investigated the living nature of ROP with TTIP where a block copolymer of PCL-PLA was achieved.

Automated summary

Ring opening polymerization (ROP) is typically conducted using anhydrous reagents and inert atmosphere, which are barriers for non-experts. Here, two new techniques for limited ROP of epsilon-caprolactone (CL) without pre-drying reagents were developed using a laboratory oven. By evaporating water in a vacuum oven or polymerizing through water with titanium isopropoxide (TTIP), variable chain lengths and molecular weight distributions of PCL were achieved, with TTIP showing better performance for higher molecular weights and block copolymer formation.