Ring-opening polymerization of lactones catalyzed by decamolybdate anion

An efficient process for the ring-opening polymerization (ROP) of lactones by ammonium decamolybdate (NH4)8[Mo10O34] (obtained in situ from thermal decomposition of ammonium heptamolybdate (Hep) (NH4)6[Mo7O24]), is reported for the first time. Polymerization of the ε-caprolactone (CL) and δ-valerolactone (VL) proceeds with quantitative conversions, and high molecular weight polyesters (Mn in the order of 104) with moderate polydispersity (Mw/Mn≤1.81) can be obtained at 150 °C in two hours using a CL/Hep molar ratio of 20,000. Hydroxylic compounds can be efficiently used to control the final molecular weight. Hydroxylic compounds act as both co-initiators and chain transfer agents. Incorporation of the hydroxylic compounds as end groups in the polymeric backbone was corroborated by 1H and 13C-NMR. The molecular weight of poly(ε-caprolactone) (PCL) measured by gel permeation chromatography (GPC) shows a linear dependence on the CL/OctOH ratio. Decamolybdate anion (isolated as a product from the thermal decomposition of heptamolybdate) shows a similar catalytic activity toward polymerization compared to that observed for ammonium decamolybdate obtained in situ. Catalysts recovered after a polymerization batch maintain most of their initial properties, and can be reused to polymerize lactones in an efficient manner.