Microwave-assisted Ring-Opening Polymerization of ε-Caprolactone in Presence of Hydrogen Phosphonates

Microwave-assisted ring-opening polymerization (MROP) of epsilon-caprolactone (epsilon-CL) in the presence of hydrogen phosphonate was investigated. Poly(epsilon-caprolactone) with molecular weight of 8100 g/mol was synthesized in 100 min at 510 W microwave irradiation in the presence of 2.9% of diisopropyl hydrogen phosphonate. It was found that the MROP of epsilon-CL was first initiated by the trace water in the reaction mixture; a subsequent transesterification reaction occurred between the oligo(epsilon-caprolactone) and diisopropyl hydrogen phosphonate at the early stage of the MROP, and the resulting oligo(epsilon-caprolactone)-substituted hydrogen phosphonate could act as the catalyst during the MROP after diisopropyl hydrogen phosphonate was consumed out.