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

The ring-opening polymerization of delta-valerolactone (delta-VL) and epsilon-caprolactone (epsilon-CL) using 3-phenyl-1-propanol (PPA) as the initiator and dipheny phosphate (DPP) as the catalyst in toluence at room temperature with the [delta-VL or epsilon-CL](0)/[PPA](0)/[DPP] ratio of 50/1/1 homogeneously proceeded to afford poly(delta-valerolactone) (PVL) and poly(epsilon-caprolactone) (PCL) with narrow polydispersity indices. The molecular weights determined from a H-1 NMR analysis (PVL, M-n,M-NMR = 5170 g mol(-1) and PCL, M-n,M-NMR = 5920 g mol(-1)) showed good agreement with those estimated from the initial of [delta-VL or epsilon-CL](0)/[PPA] and monomer conversions (PVL, M-n,M-theo = 4890 g mol(-1) and PCL, M-n,M-theo = 5680 g mol(-1)). The H-1 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 a activated monomer mechanishm. The kinectic and chain extension experiments confirmed the controlled/living nature for the DPP-catalyzed ROP of lactones. In addition, the block copolymerization of PVL and PCL successfully proceeded to afford PVL-b-PCL regardless of the monomer additon sequence. The DPP-catalyzed ROP of delta-VL and epsilon-CL using functional initiators, such as 2-hydroxyethyl methacrylate, 4-vinylbenzyl alcohol, propargyl alcohol, and 6-azido-1-hexanol, produced the corresponding end-functionalized PVLs and PCLs with narrow molecular weight distributions.