Oxidative Depolymerization of Polyphenylene Oxide into Benzoquinone

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is one of the most important engineering plastics commonly utilized in various fields. Herein, chemical recycling of PPO was performed via oxidative depolymerization to form 2,6-diemthyl-p-benzoquionone (26DMBQ) as a sole aromatic product in 66 % yield using nitronium ions (NO₂ ⁺ ) as a mild oxidant. Mechanistic studies revealed that PPO is oxidized by NO₂ ⁺ generated from the combination of a silicotungstic acid and nitrate salts, and then subsequently attacked by H₂ O to achieve C-O bond cleavage, resulting in the formation of 26DMBQ, which was sublimed at the headspace of the reaction vessel in pure form. 26DMBQ was applied to polymerization with dianilines to form polyimides. Thus, an upgrade recycling process of PPO was demonstrated.