Group Transfer Polymerization of Acrylates Catalyzed by N-Heterocyclic Carbenes

Group transfer polymerization (GTP) is an effective method for the synthesis of poly(methyl methacrylate) (pMMA) with controlled molecular weights and narrow polydispersities. Silyl ketene acetals initiate the polymerization of methyl methacrylate in the presence of either nucleophilic or Lewis acid catalysts. We report the use of N-heterocyclic carbenes (NHCs) as neutral nucleophilic catalysts for GTP of methyl methacrylate (MMA) and tert-butyl acrylate (TBA). For MMA. polymer molecular weights increase linearly with conversion and are predictable over a range of [M](0)/[I](0) ratios. Polydispersities trend downward with conversion and approach 1.2 at > 95%, conversion. Significantly, NHCs were also shown to be effective for the controlled GTP of TBA, generating living polymers with predictable molecular weights, narrow molecular weight distributions (Mw/Mn <= 1.2), and living chain ends, as illustrated by chain-extension experiments.