Room‐Temperature Lewis Acid Organocatalysts for Bulk Ring‐Opening Polymerization of Bis‐Lithium N‐Heterocyclic Carbenes Complexes Activated on ε‐Caprolactone: Synthetic, Experimental, and Density Functional Theory of Mechanistic Studies

Abstract

This work investigates the high catalytic activity of bi‐functional lithium N‐heterocyclic carbene (bisLiNHCs) complexes in bulk ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) monomer at room temperature. The study employs a bulk ROP technique using tetramethylene‐tethered bis[N‐(N′‐alkyl/arylimidazolium)] bishexafluorophosphate (bis[Bim][PF6]), benzyl alcohol (BnOH), and n‐butyl lithium (nBuLi) in molar ratios of 1:2:4. The results show that 1,4‐bisLiNHC (3a) has the highest catalytic capability, producing the highest molecular weight of PCL with acceptable dispersity in only 93 s (59 361 g mol−1, Đ = 1.8). However, longer and aromatic linker chains (3b‐3g) are found to be less effective due to the increased steric effect for complex formation with the monomer, leading to longer reaction times and lower molecular weight PCL with wider dispersity. Additionally, the study conducts a mechanistic analysis using the DFT method with B3LYP (6‐31G(d,p)) as the basis set. The most plausible mechanism proposed involves continuous and coordinated insertion with low energy barriers.