The growing production of plastics has led to an increase in waste, posing considerable environmental challenges. Polyethylene, a significant component of landfills, does not decompose under ambient conditions. Traditional mechanical recycling often diminishes the material qualities of polyethylene, limiting its long-term usefulness. An innovative technique, upcycling through dehydrogenation and functionalization, addresses this issue by enhancing the utility of recycled materials. This study explores several methods of functionalizing dehydrogenated polyethylene, using polycyclooctene (PCOE) as a model substrate, to produce materials suitable for a wide range of applications, including adhesives and elastomers. A comprehensive investigation into the structure-property relationships was conducted to understand the impact of chemical alterations on macroscopic properties, advancing the potential applications of upcycled polyethylene. In Chapter 2, thiol-ene click chemistry with mercaptoethanol was employed to functionalize PCOE with polar OH groups. The degree of C=C conversion was linked to reaction parameters, and the functionalization significantly enhanced mechanical properties, most notably increasing ultimate shear strength in a lap joint arrangement by approximately tenfold. This suggests potential for lower temperature melt processing applications. Further research may be focused to explore how varying the molecular weight of PCOE affects its structural, thermal, and mechanical properties. Chapter 3 examines the modification of PCOE with three acid-terminated linear pendants that do not require acid group protection. Increased COOH fractions improved surface polarity while influencing crystallinity and melting temperature. Although the rubbery modulus decreased, there was no significant change in the glassy modulus as determined by DMA characterization. Broadband dielectric spectroscopy revealed multiple relaxations in highly functionalized polymers, indicating potential for self-assembly applications. Chapter 4 details the successful synthesis of linear EVSA copolymers with varying degrees of thioacetate functionalization, resulting in greater stretchability and elasticity. The EVSA-25 sample demonstrated excellent elongation and intrinsic crosslinking during melt pressing, indicating a sustainable and cost-effective method for creating specialty materials. Broadband dielectric spectroscopy showed rapid relaxation of pendant groups, suggesting potential for self-healing applications. The EVSA-25 sample also exhibited exceptional elastic recovery and reprocessing capability, maintaining material properties through multiple recycling cycles. The functionalization of PCOE with polar OH groups through thiol-ene click chemistry significantly enhanced the adhesive strength, while modifications with acid-terminated linear pendants improved surface polarity and influenced crystallinity and melting temperature. Additionally, synthesizing linear EVSA copolymers with varying degrees of thioacetate functionalization resulted in greater stretchability, elasticity, and reprocessable capabilities, maintaining elasticity through two recycling cycles. These studies highlight the potential for upcycling polyethylene using environmentally friendly processes, presenting promising avenues for developing functional materials.