Living polymerization of naturally renewable butyrolactone-based vinylidenes mediated by a frustrated Lewis pair

Abstract

Renewable methylene butyrolactones, such as γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL), have received particular attention due to their high reactivity and enhanced polymer performance. However, challenges still remain in the development of a living/controlled polymerization strategy for these renewable monomers. This contribution reports an effective frustrated Lewis pair consisting of a strong organophosphorus superbase and a sterically encumbered but modestly strong organoaluminum Lewis acid to rapidly polymerize (M)MBL into polymers with a predicted molecular weight (M_n up to 195 kg mol⁻¹) and narrow molecular weight distribution (MWD as low as 1.04), thus affording high to near quantitative initiation efficiency. The livingness of MMBL polymerization catalyzed by the P(NIⁱPr)Ph₂/(BHT)₂AlⁱBu FLP was confirmed by successful chain extension experiments and the formation of well-defined copolymers. Besides, this LPP strategy also enabled the synthesis of the diblock copolymers PMMA-b-PMMBL and PEEMA-b-PMMBL by using methacrylate as a comonomer. Furthermore, a kinetic study coupled with the characterization of the active zwitterionic species led to the bimolecular, activated monomer propagation mechanism proposed for (M)MBL polymerization catalyzed by such an FLP system.