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

In the domain of polyolefin chemical recycling and upcycling, the economic viability of the resultant products is of utmost significance. Polysubstituted alkylbenzenes, especially those within the C9‐C12 alkylaromatic range, with a market price exceeding 1400 USD per ton, represent a high‐value segment with substantial yet unexploited potential for further development. Herein, we present a novel methodology that utilizes methanol as a co‐reactant, 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, Mw = 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 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 towards 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.