Dual Catalysis Based on N-Heterocyclic Olefins for the Copolymerization of Lactones: High Performance and Tunable Selectivity

Abstract

The cooperative interaction of four structurally different N-heterocyclic olefins (NHOs) with a range of simple metal halides as Lewis acidic cocatalysts is employed for the homo- and copolymerization of e-caprolactone (CL) and δ-valerolactone (VL). While the single components are inactive on their own, their combination provides a powerful and operationally simple platform for the controlled preparation of polyesters from these monomers, whereby molecular weights and end groups can be predicted in a room temperature-based process using low catalyst loadings (0.25–0.50 mol %). A narrow molecular weight distribution is observed (1.05 < ĐM < 1.15) for multiple combinations of NHOs and Lewis acids. Importantly, the supposed mechanism involves activation of the lactone monomers via coordination to the metal-based Lewis acids. This ensures rapid polymerization and additionally decouples reactivity and activity; a trade-off between fast monomer consumption and the suppression of side reactions (transesterificat...