Super engineering plastics, high-performance thermoplastic resins such as polyetheretherketone, and polyphenylene sulfide have been utilized in industries, owing to their high thermal stability and mechanical strength. However, their robustness hinders their depolymerization to produce monomers and low-weight molecules. Presently, chemical recycling for most super engineering plastics remains relatively unexplored. Herein, we report the depolymerization of insoluble polyetheretherketone using sulfur nucleophiles via carbon–oxygen bond cleavages to form benzophenone dithiolate and hydroquinone. Treatment with organic halides converted only the former products to afford various dithiofunctionalized benzophenones. The depolymerization proceeded as a solid–liquid reaction in the initial phase. Therefore, this method was not affected by the shape of polyetheretherketone, e.g., pellets or films. Moreover, this depolymerization method was applicable to carbon- or glass fiber-enforced polyetheretherketone material. The depolymerized product, dithiofunctionalized benzophenones, could be converted into diiodobenzophenone, which was applicable to the polymerization.

The solvent-insoluble poly(phenylene sulfide) main chain was reductively cleaved by using triethylsilane as a hydrogen source under palladium/IcHex catalytic conditions. After the reaction, benzene and bis(triethylsilyl)sulfide as a sulfide source were formed efficiently. This method could be operated on a gram scale.

Super engineering plastics, high-performance thermoplastic resins such as polyetheretherketone (PEEK), and polyphenylene sulfide (PPS) have been utilized in industries, owing to their high thermal stability and mechanical strength. However, their robustness hinders their depolymerization to produce monomers and low-weight molecules. Presently, chemical recycling for most super engineering plastics remains relatively unexplored. Herein, we report the depolymerization of insoluble PEEK using sulfur nucleophiles via carbon–oxygen bond cleavages to form benzophenone dithiolate and hydroquinone. Treatment with organic halides converted only the former products to afford various dithiofunctionalized benzophenones. The depolymerization proceeded as a solid–liquid reaction in the initial phase. Therefore, this method was not affected by the shape of PEEK, e.g., pellets or films. Moreover, this depolymerization method was applicable to carbon- or glass fiber-enforced PEEK material. The depolymerized product, dithiofunctionalized benzophenones, could be converted into diiodobenzophenone which is an active form of aromatic substitution reactions.