Chemical Recycling of Thiol Epoxy Thermosets via Light-Driven C–C Bond Cleavage

Abstract

Epoxy thermosets are high-volume materials that play a central role in a wide range of engineering applications; however, technologies to recycle these polymers remain rare. Here, we present a catalytic, light-driven method that enables chemical recycling of industrially relevant thiol epoxy thermosets to their original monomer at ambient temperature. This strategy relies on the proton-coupled electron transfer (PCET) activation of hydroxy groups within the polymer network to generate key alkoxy radicals that promote the fragmentation of the polymer through C–C bond β-scission. The method fully depolymerizes insoluble thiol epoxy thermosets into well-defined mixtures of small-molecule products, which can collectively be converted into the original monomer via a one-step dealkylation process. Notably, this process is selective and efficient even in the presence of other commodity plastics and additives commonly found in commercial applications. These results constitute an important step toward making epoxy thermosets recyclable and more generally exemplify the potential of PCET to offer a more sustainable end-of-life for a diverse array of commercial plastics.

Solvent–base mismatch enables the deconstruction of epoxy polymers and bisphenol A recovery

“…Recently, a photocatalytic process for disconnecting C-C bonds in epoxy polymers has been reported. 30,31 Although mild and elegant in nature, a subsequent ether cleavage using BBr 3 is necessary to release bisphenol A. As an alternative approach, we decided to target the C(alkyl)-O bonds formed during the reaction of BPA with epichlorohydrin, as their cleavage would directly liberate BPA (Fig.…”

Selective Electrocatalytic Degradation of Ether‐Containing Polymers

“…For example, the Stache group and several others have recently reported the photooxidative degradation of polystyrene to benzoic acid through a hydrogen atom transfer (HAT) mechanism [26–33] . Knowles and co‐workers have also developed light‐driven depolymerizations of hydroxylated polymers through proton‐coupled electron transfer (PCET) [34,35] . However, while photochemical methods have gained much attention for plastic valorization, the use of electrochemistry to drive polymer degradation is far less explored.…”

“…[26][27][28][29][30][31][32][33] Knowles and coworkers have also developed light-driven depolymerizations of hydroxylated polymers through proton-coupled electron transfer (PCET). [34,35] However, while photochemical methods have gained much attention for plastic valorization, the use of electrochemistry to drive polymer degradation is far less explored.…”

Closed-loop recycling of lignin-based sustainable polymers with an all-hydrocarbon backbone

“…, ester bonds and ether bonds) to the polymer backbone, which serve as the key scission sites during degradation. 4–10 These labile chemical bonds could also lead to undesirable mechanical performance reduction and depressed thermal stability compared with polyolefins. 11…”