Ring-opening polymerization of ε-caprolactone with recyclable and reusable squaric acid organocatalyst

With the increasing requirements concerning healthy and environmental issues of modern-day society, green chemistry and atomic economy have become the consensus of researchers and manufacturers, enabling us to explore much facile way to prepare biodegradable and biocompatible polyesters which have been widely utilized in many fields. Therefore, squaric acid (SA) a commercially available organic acid, was evaluated as the organocatlyst for the ring-opening polymerization (ROP) of ε-caprolactone (CL) to synthesize polyesters with benzyl alcohol (BzOH) as the initiator under bulk at a temperature of 80 °C. The polymerizations were demonstrated in a controlled/living character, allowing for the obtained PCLs with expected molecular weight and narrow dispersity. Moreover, PCL-based block copolymers and end-functionalized PCLs containing vinyl, alkynyl and pyrenyl chain-end were also prepared. Excitingly, SA can be facilely recovered and reused up to ten consecutive cycles without distinguishable decline in catalytic activity and MTT assay was performed to explore the cytotoxicity of the polymers.