Oxidative Upcycling\nof Polyolefin Wastes into the\nDynamically Cross-Linked Elastomer

Oxidative cracking of polyolefins into functionalized\nmolecules\nor oligomers promises the chemical upcycling of plastic wastes. In\nthis work, we develop a novel approach to polyolefin waste upcycling\nthat utilizes low-temperature oxidative cracking combined with dynamic\ncross-linking to produce recyclable elastomers. High-density polyethylene\nis oxidized into functionalized oligomers with end carboxyl groups\nat 110 °C, achieving tunable number-average molecular weights\n(<i>M</i><sub>n</sub>) ranging from 1500 to 5500 Da at distributions\n(<i>D̵</i>) between 2.91 and 3.33. These oligomers\nwith high crystallinity directly react with amorphous <i>cis</i>-polybutadiene containing pendant epoxy groups (an oxidized product\nof <i>cis</i>-polybutadiene) through esterification, forming\na dynamically cross-linked elastomer. The elastomer displays a low\nglass transition temperature (<i>T</i><sub>g</sub>) of approximately\n−100 °C while maintaining a melting point (<i>T</i><sub>m</sub>) above 80 °C; it showcases a Young′s modulus\n(<i>E</i>) of 12.0 ± 0.4 MPa, elongation at break (ε)\nof 600 ± 28%, tensile strength (σ) of 16.4 ± 0.8 MPa,\ntensile toughness (<i>U</i><sub>T</sub>) of 46.0 ±\n3.5 MJ·m<sup>–3</sup>, and a good elasticity with 81.8%\nelastic recovery in a 10-cycle tensile test, even higher than that\nof commercial POEs such as POE-8150 of Dow Company. The dynamic ester-bond-based\ncross-linking enables the elastomer to be reprocessed. Our study introduces\nan efficient chemical upcycling process for polyolefin wastes, eliminating\nthe need for tedious separation steps of cracking products.