Re-evaluation of the ring-opening polymerization of ε-caprolactone catalyzed by dialkylmagnesium reagents

Abstract

Herein we re-evaluate the synthesis of Poly(ε-caprolactone) (PCL) by ring-opening polymerization (ROP) using simple dialkylmagnesium compounds as catalysts. This old reaction has been never studied thoroughly before and a consensus on the intervening mechanism is lacking, being an anionic pathway proposed in the classic literature. In our hands, all tested catalysts exhibit high efficiency and complete conversion was achieved within a few hours with high yield and high number-average molecular weight (Mn) in a living fashion. Moreover, kinetic studies revealed that the ROP of ε-CL has a first order dependency on monomer (ε-CL) as well as catalyst concentration. Furthermore, mechanistic studies of the ROP demonstrated that the reaction follows a coordination-insertion mechanism where the alkyl group initiates the polymerization and is incorporated as one of the terminal groups in the polymer chain.