Polymerization of Polar Vinyl Monomers Catalyzed by Lewis Pairs

The field of the "frustrated Lewis pair" (FLP) chemistry has been receiving sustained intense interests ever since the seminal work reported by Stephan and Erker. On the one hand, the application of FLPs has now been well established in the small molecule chemistry, such as the activation of small molecules, catalytic hydrogenation reactions, and new reactivity/reaction developments. On the other hand, Lewis pair polymerization (LPP) has emerged as the hotspot and frontier of polymer synthesis and generated some exciting results in polymer synthesis, especially in the polymerization of various polar vinyl monomers. Although the polymerization promoted by LPs, either FLPs or classical Lewis adducts (CLAs), exhibited high activity for polymerization of polar vinyl monomers, the application of such polymerization is hampered by both the low initiation efficiencies and chain-termination side reactions, evidenced by the much higher obtained number-average molecular weight (M-n) than the calculated M-n and broader molecular weight distribution (MWD, or large D values) of the resulting polymers, thus giving rise to low initiation efficiencies (I*) and rendering the inability to produce well-defined block copolymers. Therefore, it remains as a challenge to achieve the living polymerization of polar vinyl monomers by a non-interacting, true FLP, or LP-promoted living polymerization of less bulky methacrylates, particularly methyl methacrylate (MMA), a very important fundamental monomer in the polymer industry. Herein, we summarized the recent developments achieved in the polar vinyl monomer polymerization by LPP since the first successful polymerization catalyzed by LP in 2010, including the scopes of monomers, investigation of reaction mechanism, and different polymerization catalyst systems based on classic Lewis acid-base adduct (CLA) or FLP. These results indicated that the synergistic effects of the LA and LB sites of LPs were essential to achieve an effective and controllable polymerization system. By choosing appropriate combination of Lewis acid and Lewis base, not only the living polymerization of polar vinyl monomer could be achieved, but also the synthesis of ultrahigh molecular weight polymer with M-n > 10(6) g mol(-1) and narrow MWD was obtained through this FLP polymerization strategy. Last but not least, with the aim to push forward the studies on LPP, more attention should be paid by chemists from but not limited to the field of frustrated Lewis pairs chemistry for the developing and enriching polymer synthesis by LPP.