High-Activity Organocatalysts for Polyether Synthesis via Intramolecular Ammonium Cation Assisted S(N)2 Ring-Opening Polymerization

摘要

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 approximate to 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 (>10(6) 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.