Activation and Deactivation of Chain-transfer Agent in Controlled Radical Polymerization by Oxygen Initiation and Regulation

Organoboron-mediated polymerizations

The scientific community has witnessed extensive developments and applications of organoboron compounds as synthetic elements and metal-free catalysts for the construction of small molecules, macromolecules, and functional materials over the last two decades. This review highlights the achievements of organoboron-mediated polymerizations in the past several decades alongside the mechanisms underlying these transformations from the standpoint of the polymerization mode. Emphasis is placed on free radical polymerization, Lewis pair polymerization, ionic (cationic and anionic) polymerization, and polyhomologation. Herein, alkylborane/O2 initiating systems mediate the radical polymerization under ambient conditions in a controlled/living manner by careful optimization of the alkylborane structure or additives; when combined with Lewis bases, the selected organoboron compounds can mediate the Lewis pair polymerization of polar monomers; the bicomponent organoboron-based Lewis pairs and bifunctional organoboron-onium catalysts catalyze ring opening (co)polymerization of cyclic monomers (with heteroallenes, such as epoxides, CO2, CO, COS, CS2, episulfides, anhydrides, and isocyanates) with well-defined structures and high reactivities; and organoboranes initiate the polyhomologation of sulfur ylides and arsonium ylides providing functional polyethylene with different topologies. The topological structures of the produced polymers via these organoboron-mediated polymerizations are also presented in this review mainly including linear polymers, block copolymers, cyclic polymers, and graft polymers. We hope the summary and understanding of how organoboron compounds mediate polymerizations can inspire chemists to apply these principles in the design of more advanced organoboron compounds, which may be beneficial for the polymer chemistry community and organometallics/organocatalysis community.

ATRP of MIDA Boronate-Containing Monomers as a Tool for Synthesizing Linear Phenolic and Functionalized Polymers

Despite numerous novel polymeric materials that have been produced by incorporating boronic acid or ester groups into polymers, it remains a challenge to prepare well-defined boronate-containing polymers due to their inherent instability. Herein, we used N-methyliminodiacetic acid (MIDA) to stabilize the reactive organoboron structure. MIDA boronate-containing polymers were synthesized in a good control by initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP). Oxidation and Suzuki-Miyaura coupling were conducted to prepare linear phenol-containing polymers and aromatic functionalized polymers. Upon comparison of similar polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, of which the chain transfer agent (CTA) end groups cause multiple undesired side reactions, the halogen end groups of polymers prepared by ATRP are nontoxic to metal catalysts and stable during the postmodifications, thus providing a more facile tool for synthesizing various functionalized polymers with great potentials in advanced materials.