Living Polymerization of Conjugated Polar Alkenes Catalyzed by N-Heterocyclic Olefin-Based Frustrated Lewis Pairs

The living polymerization of conjugated polar alkenes such as methacrylates by a noninteracting, authentic frustrated Lewis pair (FLP) has remained elusive ever since the report on FLP-promoted polymerization in 2010. Here we report that the polymerization of alkyl methacrylates by a FLP system based on a strongly nucleophilic N-heterocyclic olefin (NHO) Lewis base and sterically encumbered but modestly strong Lewis acid MeAl(4-Me-2,6-tBu2-C6H2O)2 is not only rapid but also living. This living polymerization was indicated by the formation of a linear, living chain, capped with NHO/H chain ends, without backbiting-derived cyclic chain ends. The true livingness of this FLP-promoted polymerization has been unequivocally verified by five lines of evidence, including the predicted polymer number-average molecular weight (Mn, up to 351 kg·mol–1) coupled with low dispersity (Đ = 1.05) values; obtained high to quantitative initiation efficiencies; an observed linear increase of polymer Mn vs monomer conversion and the monomer-to-initiator ratio; found precision in multiple chain extensions; and formed well-defined diblock and ABA triblock copolymers with narrow molecular weight distributions (Đ = 1.09–1.13), regardless of the comonomer addition order.