Creating Remarkably Moisture- and Air-Stable Macromolecular Lewis Acid by Integrating Borane within the Polymer Chain: A Highly Active Catalyst for Homo(co)polymerization of Epoxides

Borane-based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane-based LPs are moisture- and air-sensitive. Therefore, development of moisture and air-stable borane-based LP is highly desirable. To achieve this goal, the concept of "aggregation induced enlargement effects" by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP-1B featuring poly(4-vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP-1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 degrees C (TOF=27900 h-1). Furthermore, it enables generation of well-defined telechelic poly (CHO-alt-CO2) diol (0.6-15.3 kg/mol) with narrow Ds via copolymerizing cyclohexene oxide and CO2 at 80 degrees C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers. Borane-based Lewis acids play an indispensable role in organocatalyst-mediated polymerization, but most of them are moisture- and air-sensitive. This work presents a remarkably moisture and air-stable macromolecular borane Lewis acid, employing an integration strategy to unify multiple borane within a polymer chain. It functions as a highly active catalyst for homo(co)polymerization of epoxides (TOF=27900 h-1) and shows large tolerance to chain transfer agent (1800 equiv. H2O).image