Scalable and Room-Temperature Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Active Lithium Tetramethylene-Tethered [-('-butylimidazol-2-ylidene)] -Heterocyclic Carbene as a Lewis Acid Organocatalyst.

The Lewis acid organocatalytic system of lithium tetramethylene-tethered [-('-butylimidazol-2-ylidene)] -heterocyclic carbene (1,4-NHC) including lithium benzyloxide and benzyl alcohol has been successfully utilized in the ring-opening polymerization (ROP) of ε-caprolactone (CL) for the first time. The catalytic performance of this organic catalyst in the synthesis of high-molecular-weight polymers was investigated via bulk polymerization using different combinations of tetramethylene-tethered [-('-butylimidazolium)] hexafluorophosphate (1,4-[Bim][PF]), benzyl alcohol (BnOH), and -butyl lithium (BuLi) ([1,4-[Bim][PF]]/[BnOH]/[BuLi]) with the molar ratios of 0:2:2, 1:1:3, 1:2:3, and 1:2:4. The results showed that the molar ratio of 1:2:3 efficiently and rapidly initiated the bulk ROP of CL at room temperature with a high molar ratio of CL to 1,4-[Bim][PF] of 3000/1 and produced the highest number of average-molecular-weight () poly(ε-caprolactone) (103,057 g mol) with the dispersity () and %conversion of 1.73 and 98% in a short period of time (152 s). From comparative studies, the relative polymerization rates of the bulk ROP of CL with different [1,4-[Bim][PF]]/[BnOH]/[BuLi] molar ratios was determined in the following order: 1:2:4 > 1:1:3 > 1:2:3 > 0:2:2. For mechanistic investigation, the bulk ROP mechanism of CL with our organic catalyst was proposed through the intramolecular -lithium-carbene interaction pathway for 1,4-NHC, 1,4-NHC, and 1,4-NHC systems.