Oxidative Upcycling of Polyolefin Wastes into the Dynamically Cross-Linked Elastomer

Oxidative cracking of polyolefins into functionalized molecules or oligomers promises the chemical upcycling of plastic wastes. In this work, we develop a novel approach to polyolefin waste upcycling that utilizes low-temperature oxidative cracking combined with dynamic cross-linking to produce recyclable elastomers. High-density polyethylene is oxidized into functionalized oligomers with end carboxyl groups at 110 °C, achieving tunable number-average molecular weights (M_n) ranging from 1500 to 5500 Da at distributions (D̵) between 2.91 and 3.33. These oligomers with high crystallinity directly react with amorphous cis-polybutadiene containing pendant epoxy groups (an oxidized product of cis-polybutadiene) through esterification, forming a dynamically cross-linked elastomer. The elastomer displays a low glass transition temperature (T_g) of approximately −100 °C while maintaining a melting point (T_m) above 80 °C; it showcases a Young′s modulus (E) of 12.0 ± 0.4 MPa, elongation at break (ε) of 600 ± 28%, tensile strength (σ) of 16.4 ± 0.8 MPa, tensile toughness (U_T) of 46.0 ± 3.5 MJ·m^–3, and a good elasticity with 81.8% elastic recovery in a 10-cycle tensile test, even higher than that of commercial POEs such as POE-8150 of Dow Company. The dynamic ester-bond-based cross-linking enables the elastomer to be reprocessed. Our study introduces an efficient chemical upcycling process for polyolefin wastes, eliminating the need for tedious separation steps of cracking products.