Catalytic thiolation-depolymerization of oxyphenylene type super engineering plastics via selective carbon-oxygen main chain cleavages

Abstract As the effective use of carbon resources has become a pressing societal issue, the importance of chemical recycling of plastics has increased. The catalytic depolymerization method for plastics is a promising approach for creating valuable products under efficient and mild conditions. Although depolymerization methods for various commodity plastics and several engineering plastics have been developed, the degradation of robust super engineering plastics that have very high heat resistance, chemical resistance, and low solubility is nearly unexplored. Herein, we report the catalytic depolymerization of oxyphenylene-based super engineering plastics such as polyetheretherketone, polysulfone, and polyetherimide using thiols via selective carbon–oxygen main chain cleavage to form monomer-type molecules, electron-deficient arenes with sulfur functional groups and bisphenols. The catalyst combination of a bulky phosphazene base P4-tBu with inorganic bases such as tripotassium phosphate or cesium carbonate enabled smooth depolymerization by activating the thiols to form reactive thiolates. This depolymerization method could be utilized with carbon- or glass fiber-enforced polyetheretherketone materials and a consumer resin. The sulfur functional groups in one product could be transformed to amino and sulfonium groups and fluorine by using suitable catalysts. Notably these fluorinated products are the monomers of the parent super engineering plastics.