Since decades, the accumulation of plastic waste is a global problem as most post-consumer plastics are landfilled or incinerated, heavily affecting the planet. Additionally, methods such as mechanical recycling often cause degradation of polymers, resulting in lower-value products. One solution to this societal problem is to redesign plastics to allow closed loop recycling or upcycling of these materials, e.g., by introducing cleavable or dynamic bonds in the polymer backbone. In this context, polyethylene (PE) is amongst the most widely produced plastics. However, the outstanding properties that make PE so versatile also make its (chemical) recycling extremely challenging. This research proposal is devoted to finding a solution to this problem by investigating industrially relevant and scalable pathways for preparing PE-like materials with properties that are equal or superior to those of standard PE, but which contain cleavable bonds (i.e., aminals or acetals). This will be achieved through the synthesis of novel cyclic monomers able to undergo ring-opening metathesis copolymerization with cyclooctene. Through acidic hydrolysis of these polymers, we will obtain PE-like macromonomers that can be converted back to the initial PE-like polymers by polycondensation. Additionally, these macromonomers will be upcycled by combining them with dynamic bonds. This way, thermoplastic materials with high molar mass and higher processability will be obtained.