LAUSR

Polyolefins are an indispensable class of materials that have become the most widely produced and utilized polymers today. They are readily synthesized from cheap and abundant monomer feedstocks, such as ethylene and propylene, and are capable of achieving a vast array of thermal and mechanical properties based upon their composition and topology. However, despite their numerous advantages, polyolefins are typically devoid of functional groups which can limit their applicability to many product families, such as coatings, adhesives, and cross-linked polyolefins. To overcome this issue, researchers typically employ postpolymerization modification techniques to access functionalized polyolefins. These strategies can include functionalization using free radical chemistry, deprotection of incorporated comonomers bearing latent functionality, as well as numerous other methods. Though many of these post-polymerization modification strategies are currently implemented on an industrial scale, they require additional synthetic steps that incur added reagent and energy consumption costs. In contrast, if functionalized polyolefins could be synthesized via the direct copolymerization of olefins and polar comonomers, multiple advantages may be realized (Figure 1). These could include avoiding additional synthetic steps, more uniform functional group placement, and retention of polymer properties that might otherwise be degraded during post-polymerization modification. Toward this goal, researchers have turned to the development of group 10 olefin polymerization catalysis capable of copolymerizing simple olefins (ethylene and α-olefins) with polar functionalized vinyl comonomers. These group 10 catalysts generally employ Ni or Pd active metal centers, and are less oxophilic than their early transition metal analogues. Because of this, they are able to tolerate and incorporate polar comonomers more readily. Though Pd-based catalysts generally achieve higher polar comonomer incorporation percentages, they typically exhibit lower activities and/or produce lower molecular weight polymers than their Nibased analogues. It is for these reasons that the development of Ni-based olefin polymerization catalysts capable of incorporating polar comonomers is of utmost interest to academia and industry alike. Herein, we will describe three recent examples that highlight these efforts. One of the most frequently targeted classes of polar comonomers are those containing ester functionalities. This is in part due to the vast availability of ester functionalized monomers, as well as their ability to significantly tailor a polyolefin’s surface energy and interactions. An example of these efforts was reported by Coates and coworkers [1] who developed a cationic Ni catalyst bearing a bulky dibenzobarrelene-derived α-diimine ligand. This catalyst displayed living ethylene polymerization behavior at room temperature and produced highly linear polyethylene (Tm≤135 °C) at polymerization temperatures ≤20 °C. Furthermore, this unique catalyst was able to incorporate the ester-functionalized comonomer, methyl 10-undecenoate, to yield semi-crystalline copolyethylenes (Tm=97–128 °C) with high molecular