<p>Accumulation of plastic waste in the environment is not only a pressing environmental problem but also a waste of resources. Developing chemically recyclable plastics is deemed a viable approach to address the ever-growing plastic crisis, but the synthesis of circular polyolefins remains challenging. Here we demonstrate a ring-strain matched concept for the tailored synthesis of circular polyolefins. By designing a well-defined 16-membered unsaturated lactone (Ester-16), a family of chemically recyclable, high-molecular-weight, high-density polyethylene (HDPE)-like materials is produced by the copolymerization of cyclooctene (COE) with Ester-16, followed by exhaustive hydrogenation. These HDPE-like materials have the desirable bulk properties of HDPE. They can be degraded into a well-defined and easily separable macromonomer, specifically AB-like telechelic PE. The molecular weight of the macromonomer can be precisely tailored as required and depends solely on the feed ratio of [COE]/[Ester-16]. The recycled macromonomer can be easily repolymerized into a high-molecular-weight HDPE-like material. This macromonomer–polymer–macromonomer lifecycle rather than monomer–polymer–monomer lifecycle can be repeated with quantitative yields using a facile isolation process. Overall, this work opens opportunities to improve the sustainability of plastics.</p>