A mechanistic and kinetic study of the ring‐opening polymerization of ϵ‐caprolactone (CL) in the presence of a poly(ethylene glycol) (PEG)/calcium hydride (CaH2) co‐initiation system was conducted in the bulk over a range of polymerization temperatures (70 − 133 °C). The resultant polycaprolactone‐block‐poly(ethylene glycol)‐block‐polycaprolactone (PCL/PEG/PCL) triblock copolymers were characterized by 1H NMR and gel permeation chromatography. Analysis of polymerization kinetics using Fourier transform Raman spectroscopy and 1H NMR spectroscopy showed that, relative to other reported calcium‐based initiating systems, the observed rates of polymerization for the synthesis of the PCL/PEG/PCL triblock copolymers using the PEG/CaH2 co‐initiator were much lower than expected. This was presumed to be due to the incomplete reaction of PEG with CaH2. Even so, complete consumption of PEG hydroxyl groups occurred during polymerization and the molecular weight of PCL/PEG/PCL triblock copolymers could be predicted from the molar feed ratio, [CL]0:[PEG]0. This phenomenon was proposed to be due to a fast, reversible transfer process that allowed for the controlled synthesis of PCL/PEG/PCL copolymers using this simple CaH2‐based initiating system. © 2014 Society of Chemical Industry