Neutral Silicon-Based Lewis Pairs for Living Polymerization of N,N-Dialkylacrylamide Monomers

The development of neutral silicon-based Lewis acids (LAs) has gained increasing attention, their use as catalysts for polymerization reactions has not yet been reported. Herein, we report a neutral silicon-based Lewis pair (LP) catalytic system composed of Si(catR)2 (R = H, Cl, Br, tBu) LAs and N-heterocyclic olefin (NHO) for the living polymerization of acrylamide monomers. The coordination behavior between monomers and Si(catR)2 with varying Lewis acidities was elucidated by single-crystal X-ray diffraction and in situ NMR analysis. The Si(catH)2/NHO pair exhibited high catalytic activity and control under ambient conditions, enabling the polymerization of N,N-dimethylacrylamide with high molecular weights (up to 576 kg·mol-1) and low dispersities (Đ = 1.13-1.22). MALDI-TOF-MS and chain-extension studies confirmed the living nature of the system. The scope was extended to other acrylamides, including N,N-diethylacrylamide and N,N-diallylacrylamide, allowing the synthesis of well-defined block copolymers with preserved pendant functionality and clear microphase separation behavior as confirmed by DSC. This work constructs a metal-free neutral silicon-based Lewis pair catalytic platform dedicated to the controlled synthesis of polyacrylamides, expands the library of main-group Lewis pair catalysts, and offers a novel synthetic strategy for fabricating functional precision polymers available for postpolymerization modification.