High‐Activity Organocatalysts for Polyether Synthesis via Intramolecular Ammonium Cation Assisted S_N2 Ring‐Opening Polymerization

Abstract

This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring-opening polymerization (ROP) of epoxides under mild conditions. The bifunctional catalyst incorporates two 9-borabicyclo[3.3.1]nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>10⁶ g mol^-1 ). Based on the investigations on crystal structure of catalyst, MALDI-TOF, and ¹¹ B NMR spectroscopy, an intramolecular ammonium cation assisted S_N 2 mechanism is proposed and verified by DFT calculations.