Advancements in efficient synthesis and polymer utilization.

Chemical recycling of plastics into monomers offers a promising strategy for addressing global plastic pollution. However, most chemical recycling methods are limited to specific polymers. Pyrolysis offers generality for universal polymer recycling; however, overheating leads to energy inefficiencies and degradation products, which limits its practicality. Herein, we report a photothermal depolymerization approach that is general to numerous polymers with high selectivity. Distinct from previous approaches, we identify a porous carbon material derived from proteins as a high-surface-area photothermal agent that does not require direct incorporation into polymer resin. Using low carbon loadings, we successfully depolymerize a wide range of polymers, including polystyrene (PS), poly(methyl methacrylate) (PMMA), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), trans-polyisoprene, polypropylene carbonate (PPC), poly(L-lactide) (PLLA), polyethylene terephthalate (PET), and polycarbonate (BPA-PC). Additionally, the porous carbon material is reusable at least five times by sequentially adding polystyrene films to the post-reacted porous carbon materials. Excitingly, this method is broadly applicable to post-consumer plastics without preprocessing and is readily scalable, demonstrating the versatility of this closed-loop chemical recycling approach.

Chemical recycling of plastics into monomers is a promising strategy to achieve a circular economy. However, selective depolymerization methods for mixed plastics are still underdeveloped. Herein, we report a selective and sequential depolymerization strategy for mixed plastics, including poly(L-lactide) (PLLA), polystyrene (PS), and poly(ethylene terephthalate) (PET), using photothermal conversion. We were able to selectively depolymerize PLLA into L-lactide in the presence of PS and PET. Then, PS was selectively depolymerized to styrene, followed by the depolymerization of PET into its monomer. Our protocol was carried out in one pot without any additional purification of the unreacted plastics at each stage. This method was successfully applied to mixtures of post-consumer waste plastic.

Phenol is a commodity chemical frequently used in the manufacturing of resins, pharmaceuticals, and polymers. Yet, its industrial production from cumene requires harsh oxidative conditions followed by the Hock rearrangement. Polystyrene (PS) is a widely manufactured commodity polymer; however, it is among the least recycled plastics. Intriguingly, it is composed of contiguous cumene repeats that could serve as a phenol source, enhancing its value as a waste material. In this work, we leverage the similarity between cumene and PS to drive phenol production via a mild photooxidative HAT mechanism. Using Eosin Y under blue light irradiation and atmospheric pressure of oxygen, commercial PS resin was converted into hydroperoxyl PS. Subsequent acid-catalyzed Hock rearrangement afforded up to 21% yield of phenol. The photooxidation system was successfully applied to 8 post-consumer PS plastics, achieving phenol yields up to 23%, comparable to those of the current industrial Hock process. Our method introduces a mild catalytic strategy for converting post-consumer PS into phenol, offering a potential pathway for PS waste valorization.