Synthesis of PCL–PEG–PCL Triblock Copolymer via Organocatalytic Ring-Opening Polymerization and Its Application as an Injectable Hydrogel—An Interdisciplinary Learning Trial

Biocompatible and biodegradable block copolymers composed of poly(ethylene glycol) (PEG) and aliphatic polyester are a class of promising biomaterials. Herein, a teaching experiment was designed to furnish undergraduates with a reliable method to synthesize an amphiphilic poly(ε-caprolactone)-PEG-poly(ε-caprolactone) (PCL–PEG–PCL) triblock copolymer via ring-opening polymerization of ε-caprolactone using PEG as the macroinitiator and diphenyl phosphate as the green organocatalyst; the concentrated solution of synthetic polymer in water was then demonstrated as an injectable thermogel with a sol–gel transition upon heating. Ten students serving as volunteers successfully synthesized PCL–PEG–PCL copolymer, and then analyzed their specimens using various techniques including proton-nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry, and X-ray diffraction and learned the principles of instruments. Finally, students prepared an aqueous polymer solution, and observed its interesting spontaneous physical gelation upon heating via the tube-inverting approach and dynamic rheological analysis. The experimental features captured the students' attention and made them more enthusiastic participants. This newly designed teaching experiment afforded senior undergraduates an excellent opportunity to consolidate basic concepts and principles in books with practical experimental sessions in the field of polymer chemistry, analytical chemistry, and materials science.