Polymerization of ε-Caprolactam to Nylon-6 Catalyzed by Barium σ-Borane Complex under Mild Condition

A mild and low-temperature synthesis of nylon-6 is achieved through the ring-opening polymerization of epsilon-caprolactam using barium sigma-borane complex as the catalyst. Due to the mild nature of the catalyst, this protocol provides an easy means of synthesizing nylon-6, for the first time with a precise and predictable molecular weight. From various model experiments, it is evident that the sigma-coordinated boron hydride acts as a mild hydride donor in the first step of the reaction to generate lactamate anions, which then undergo ring-opening polymerization in-situ with the remaining caprolactam molecules under the influence of the dehydrogenated boron metal complex.