Methanol-Facilitated Cascaded Polyolefin Upcycling Enabling the Efficient Generation of High-Value C₉₊ Alkylaromatics

Existing polyolefin chemical recycling and upcycling strategies predominantly yield fuels, waxes, and olefins, which are characterized by relatively low economic value. Although attempts have been made to synthesize functionalized chemicals, a particularly promising product category-C₉-C₁₂ polysubstituted alkylbenzenes with a market price exceeding 1400 USD per ton-remains largely overlooked. Herein, we present a novel methodology that utilizes methanol as a coreactant, with the goal of achieving high-yield synthesis of polysubstituted alkylbenzenes. Under mild reaction conditions (280 °C), the process attains a 97.8% conversion rate of low-density polyethylene (LDPE, M_w = 300 kDa) and complete conversion of methanol. Based on the mass of polyethylene, it produces 37 wt% of aromatic products, accompanied by an 87% increase in the mass yield of C₉-C₁₂ alkylbenzenes. Isotope-labeling experiments conducted with ¹³CH₃OH and in situ FTIR disclose that methanol acts synergistically to promote carbocation-mediated C─C bond cleavage and self-amplifying Friedel-Crafts alkylation reactions. This mechanism steers the methylative homologation pathway toward the formation of polymethylated aromatics. The versatility of this approach, which is applicable to a wide variety of polyolefins, holds the promise of opening new pathways for a profitable circular economy in the plastics industry.