Plastics are a crucial technology that have enabled the advancement of modern society. Major aspects of daily life involve in one way or another the use of polymeric materials, like the use of underground pipes for water transport or containers to preserve food. Today, plastics are mostly applied for packaging of consumer goods. Polyolefins, like polyethylene and polypropylene, have prospered as packing materials due to their lightweight, stability and inexpensive production. Single-use consumer habits has promoted an excessive production of polyolefins. As a result, the accumulation of highly durable materials is a growing problem and an environmental threat. Chapter one reviews current and emerging copolymer technologies used for the compatibilization of recycled polyolefin blends. These materials can be reused in place of newly manufactures resins of comparable value and performance. Chapter two discusses the synthesis, characterization, and application of a Ni(II) a-diimine catalyst for the production of polyethylene block copolymers. This type of complex can produce both linear and branched polyethylene via a chain-walking polymerization. In addition, the Ni catalyst exhibits living behavior allowing for the synthesis of well-defined polyethylene block copolymers. The ability of the block copolymer to compatibilize an immiscible HDPE/LDPE blend is also discussed. Chapter three focuses on the design and study of a Pd(II) a-diimine complex for the synthesis of linear polyethylene from renewable olefin feedstocks. The use of a Pd center with rapid chain-walking and a large a-diimine ligand, that promotes 2,1-insertion, results in the selective chain-straightening polymerization of light a-olefins. The copolymerization of functionalized a-olefins to produce high-value polyethylene type materials is reported. Chapter four discusses the development of temporally controlled initiation in the living polymerization of ethylene. The method allows for tuning the molecular weight of linear polyethylene as well as the shape and breadth of its molecular weight distribution. The effects of the molecular weight distribution shape and breadth on the tensile and rheological properties of the polymers are also studied.