1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

摘要

The ring-opening polymerization of ε-caprolactone (ε-CL) and rac -lactide ( rac -LA) under solvent-free conditions and using 1- n -butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO₂) as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). BMIM-2-CO₂ acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation , either by heating under vacuo (method A) or by addition of NaBPh₄ (method B). Possible catalytic and deactivation mechanisms are proposed.