Polyolefins are high-volume, low-cost thermoplastics with high tensile strength, ductility, thermal stability, and chemical inertness. The high demand for polyolefins is driven by their durability and versatility with annual production scales greater than 150 million tons, constituting 40% of global plastic production. While their primary application is in the packaging industry, polyolefins have also found utility in electrical insulation, pipes, automotive components, and medical devices. However, their mechanical resilience and chemical inertness constrain their potential applications due to their inability to be interfaced with polar additives or fillers. Additionally, the challenge of recycling polyolefins is evident, with only 14% of polyethylene recycled as recently as 2015. These low recycling rates are a consequence of destructive chain scission events during mechanical reprocessing or chemical modification recycling approaches that degrade their thermomechanical properties. Ongoing efforts have, thus, focused on the incorporation of polar groups into polyolefins to enhance their properties, aiming to create highervalue polymers with a broader range of applications and improved recyclability. Several approaches have been developed for the introduction of polar functional groups into polyolefins. Copolymerization of an a-olefin with a polar monomer is one approach that has been studied extensively, 2,5,10-14 yet demonstration of this approach has been limited because the transition metal catalysts used in copolymerization are either poisoned by polar comonomers or exhibit insufficient catalytic activity in their presence. A more promising approach involves the functionalization of C-H bonds in polyolefins. While free radical-mediated processes can be used here, they often lack chemoselectivity, leading to undesirable b-scission or crosslinking side reactions that compromise improvements in the physical properties of polyolefins. Transition-metal catalyzed C-H functionalization in polyolefins, exemplified by Rh, Cu, Ir, Mn, and Ni 31 catalysts has succeeded in minimizing deleterious side reactions, yet many of these catalysts exhibit low turnover numbers. To gain a deeper understanding of transition metal-catalyzed C-H functionalization in polyolefins, first-principles calculations are invaluable for identifying promising active site motifs and deciphering reaction mechanisms and their corresponding energy profiles. Notably, C-H oxidation in polyolefins involves a highly active but transient metal-oxo intermediate for C-H activation akin to those observed in enzymes, and other homogeneous and heterogeneous catalysts. Computation can elucidate the role of this fleeting metal-oxo species, which is difficult to characterize experimentally. It can also aid in unraveling the influence of spin state on reactivity and the manifestation of multistate reactivity, both crucial for optimizing catalytic activity in C-H oxidation.