The use of ionic liquids as an organocatalyst for controlled ring-opening polymerization of ϵ-caprolactone

•Controlled ring-opening polymerization in bulk catalyzed by ionic liquid.•Living polymerization with good conversions and molecular weight distributions.•Systematic study of effect of counter ions of ionic liquids.•Kinetic study by in situ FTIR analysis.•Activation mechanism based on role of the hydrogen donor.

The controlled ring-opening polymerization of ϵ‑caprolactone in bulk catalyzed by ionic liquids, thus, avoiding the use of metal catalyst, solvent and base, is reported. These mild conditions led to living polymerization with good conversions and molecular weight distributions of poly(ϵ‑caprolactone). Finally, an activation mechanism is suggested based on the results of an in-situ FTIR polymerization analysis using various ionic liquid catalysts.