Diphenyl Phosphate as an Efficient Cationic Organocatalyst for Controlled/Living Ring-Opening Polymerization of δ-Valerolactone and ε-Caprolactone

Abstract

The ring-opening polymerization of δ-valerolactone (δ-VL) and e-caprolactone (e-CL) using 3-phenyl-1-propanol (PPA) as the initiator and diphenyl phosphate (DPP) as the catalyst in toluene at room temperature with the [δ-VL or e-CL]0/[PPA]0/[DPP] ratio of 50/1/1 homogeneously proceeded to afford poly(δ-valerolactone) (PVL) and poly(e-caprolactone) (PCL) with narrow polydispersity indices. The molecular weights determined from a 1H NMR analysis (PVL, Mn,NMR = 5170 g mol−1 and PCL, Mn,NMR = 5920 g mol−1) showed good agreement with those estimated from the initial ratio of [δ-VL or e-CL]0/[PPA]0 and monomer conversions (PVL, Mn,theo = 4890 g mol−1 and PCL, Mn,theo = 5680 g mol−1). The 1H NMR, SEC, and MALDI-TOF MS measurements of the obtained PVL and PCL clearly indicated the presence of the initiator residue at the chain end, confirming that the DPP-catalyzed ROP of lactones proceeded through an activated monomer mechanism. The kinetic and chain extension experiments confirmed the controlled/living nature f...