Controlled/Living Ring-Opening Polymerization of δ-Valerolactone Using Triflylimide as an Efficient Cationic Organocatalyst

The polymerization of δ-valerolactone (δ-VL) using 3-phenyl-1-propanol (3-Ph-PrOH) as the initiator and trifluoromethanesulfonimide (HNTf2) as the catalyst in CH2Cl2 at 27 °C with the [δ-VL]0/[3-Ph-PrOH]0/[HNTf2]0 ratio of 100:1:0.1 proceeded homogeneously to afford a poly(δ-valerolactone) (PVL) with a narrow polydispersity index. The molecular weight determined from the 1H NMR analysis, Mn = 9600 g mol−1, fairly agreed with that estimated from the initial ratio of [δ-VL]0/[3-Ph-PrOH]0, Mn,theo = 9400 g mol−1. In addition, the kinetic and chain extension experiments confirmed that the HNTf2-catalyzed ROP proceeded in a living fashion. The 1H NMR, SEC, and MALDI-TOF MS measurements of the obtained PVL clearly indicated the presence of the initiator residue at the chain end, showing that the HNTf2-catalyzed ROP of δ-VL proceeded through a living mechanism. The HNTf2-catalyzed ROP of δ-VL with functional initiators, such as 6-azido-1-hexanol, 2,3,4,5,6-pentafluorobenzyl alcohol, and N-(2-hydroxyethyl)maleimide, successfully afforded the corresponding end-functionalized PVL with a precise molecular control.