Imidodiphosphoric acid as a bifunctional catalyst for the controlled ring-opening polymerization of δ-valerolactone and ε-caprolactone

Imidodiphosphoric acid (IDPA) catalyzed ring-opening polymerization (ROP) of δ-valerolactone (δ-VL) and ε-caprolactone (ε-CL) with benzyl alcohol (BnOH) as the initiator in toluene at room temperature was investigated. The overall conversions of δ-VL and ε-CL to poly(δ-valerolactone) (PVL) and poly(ε-caprolactone) (PCL), respectively, were more than 90%. Experimental results indicated the living nature of the polymerizations. The polymerization reactions with different monomer-to-initiator ratios proceeded homogeneously to afford PVL and PCL with controlled molecular weight and narrow polydispersities. ¹H NMR and MALDI-TOF MS measurements demonstrated the quantitative incorporation of the initiator in the polymer chains. The controlled/living character of the polymerization was examined thoroughly by the kinetics and chain extension experiments, indicating that the IDPA-catalyzed ROPs of δ-VL and ε-CL proceeded through a living mechanism.