N-Heterocyclic carbenes: Effective organic catalysts for living polymerization

An organocatalytic approach to living and condensation polymerization using N-heterocyclic carbenes as nucleophilic catalysts is detailed. The N-heterocyclic carbene catalyst platform is extremely versatile with the nature of the substituents having a pronounced effect upon catalyst stability and activity towards different substrates. Rapid screening of libraries of catalysts provided a basic understanding of catalyst structure (sterics, electronics, etc.) as it influences the polymerization rate, control, substrate and range of molecular weights. ROP from an immiscible ionic liquid (precatalyst reservoir) and a THF solution of monomer and initiator is presented as a simplified method of carbene formation. In situ activation of the ionic liquid generated a nucleophilic N-heterocyclic carbene, which migrates to the organic phase effecting ROP. Other simplified methods of generating carbene thermally from carbene adducts are also presented as polymerization catalysts.