Hydroxylation-Depolymerization of Oxyphenylene-Based Super Engineering Plastics To Regenerate Arenols

Abstract

Super engineering plastics, high-performance thermoplastic resins, show high thermal stability and mechanical strength as well as chemical resistance. On the other hand, chemical recycling for these plastics has not been developed due to their stability. This study describes depolymerization of oxyphenylene super engineering plastics via carbon–oxygen main chain cleaving hydroxylation reaction with an alkali hydroxide nucleophile. This method is conducted with cesium hydroxide as a hydroxy source and calcium hydride as a dehydration agent in 1,3-dimethyl-2-imidazolidinone, which provides hydroxylated monomers effectively. In the case of polysulfone, both 4,4′-sulfonyldiphenol (bisphenol S) and 4,4′-(propane-2,2-diyl)diphenol (bisphenol A) were obtained in high yields. Other super engineering plastics such as polyethersulfone, polyphenylsulfone, and polyetheretherketone were also applicable to this depolymerization.

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

“…The reaction at lower temperatures (120 and 100 °C) decreased the yield (Table 1 , Entries 11 and 12). As mentioned above, PEEK is insoluble in organic solvents, but previous studies 39 , 40 showed that solvents affect the reactivity of the decomposition. So, we checked the solvent effects for this decomposition in detail.…”

“…The electron-deficient carbonyl group in the PEEK main chain enhances the reactivity of the carbon-oxygen bond at the para position such that the highly nucleophilic thiolate reagents cleave this bond selectively. We applied this system to the chemical decomposition of PSU, PESU, and PEEK using stoichiometric amounts of CsOH·H 2 O and CaH 2 to form the corresponding bisphenols 40 . We expected that these stoichiometric methods have the potential to be applied to base-catalyzed chemical decomposition of various super engineering plastics.…”

Degradation of a Wholly Aromatic Main-Chain Thermotropic Liquid-Crystalline Polymer Mediated by Superbases

“…However, significant differences were not observed, probably due to the excess methanol, 146 and 200 equiv for 4.3 and 6.4 mL of methanol, respectively, relative to the ester bonds in Vectra. Compared with the degradation of other superengineering plastics, which requires high pressure, temperature, and excess reagents, − this condition was significantly mild, efficient, and low energy consumption.…”

“…On the other hand, the inherent chemical inertness of these plastics hinders their chemical recyclability. Some degradation methods of these high-performance plastics have been reported. − However, heating at high temperatures, excess additives and reagents, and high boiling-point solvents have been used to cleave bonds in such high-performance plastics. The efficient degradation of high-performance plastics under relatively mild conditions was reported recently .…”

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

“…We applied this system to the depolymerization of PSU, PESU, and PEEK using stoichiometric amounts of CsOH•H 2 O and CaH 2 to form the corresponding bisphenols. 33 We expected that these stoichiometric methods have the potential to be applied to base-catalyzed depolymerization of various super engineering plastics. Since the previous reaction system permitted smooth depolymerization under a moderate reaction temperature (150 °C), the proposed catalytic strategy is expected to enable equally mild depolymerization to provide monomer-type products in high yields.…”