Transition‐metal‐catalyzed copolymerization of olefins with polar monomers represents a challenge because of the large variety of substrate‐induced side reactions. However, this approach also holds the potential for the direct synthesis of polar functionalized polyolefins with unique properties. After decades of research, only a few catalyst systems have been found to be suitable for this reaction. Some major advances in catalyst development have been made in the past five years. This Minireview summarizes some of the recent progress in the extensively studied Brookhart and Drent catalyst systems, as well as emerging alternative palladium and nickel catalysts.

Product morphology control represents a critical challenge for polyolefin production, but it has remained largely unexplored in the field of ethylene–polar monomer copolymerization. Herein, an ionic cluster strategy was designed to control the product morphology during the synthesis of polar-functionalized polyolefins via precipitation polymerization. In addition to product morphology control, simultaneous improvements in the catalytic copolymerization performance (activities, copolymer molecular weights, and comonomer incorporation ratios) were achieved. These results were due to less poisoning of the metal-salt-based comonomers compared with their ester counterparts and the high local concentration of the alkene comonomers induced by ionic cluster formation. Moreover, the ionic cluster strategy is generally applicable to various comonomers and catalytic systems, greatly enhances the catalyst’s thermal stability at high temperatures (90–150 °C), and enables the homopolymerization of both terminal and internal polar-functionalized olefins. Finally, polar-functionalized polyolefins and polyolefin composites (generated from a tandem process combining a prepolymerization step and subsequent polymerization) were developed, which showed tunable mechanical properties and great potential as compatibilizing agents for mixtures of polyolefins and other types of polymers.

Polyethylenes enjoy wide applications due to their many superior properties. The incorporation of some polar functional groups into the otherwise nonpolar polyethylene backbone can significantly improve many important properties and further broaden their applications. During the past few decades, many catalyst systems have been demonstrated with the capabilities of copolymerizing ethylene with polar monomers. As a result, numerous polar functionalized polyethylenes have been prepared bearing various polar groups. However, the studies into material properties of functional polyethylenes from transitionmetal-catalyzed ethylene−polar monomer copolymerization have not received much attention until recently. After some brief discussions of selected examples of potent catalysts and suitable polar monomers, this Perspective summarizes some recent advances in the improvements in surface and compatibilities properties (hydrophilicity, adhesion, dyeability, and compatibility with other types of polymers) induced through polar group incorporation as well as some custom-made properties such as elastic, flameretardant, antibacterial, antioxidant, cross-linking, self-healing, light response, dynamic cross-linking, and photodegradation properties.

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