Chemical upcycling of polystyrene into targeted small molecules is desirable to reduce plastic pollution. Herein, we report the upcycling of polystyrene to benzoyl products, primarily benzoic acid, using a catalyst-controlled photooxidative degradation method. FeCl3 undergoes a homolytic cleavage upon irradiation with white light to generate a chlorine radical, abstracting an electron-rich hydrogen atom on the polymer backbone. Under the oxygen-rich environment, high MW polystyrene (>90 kg/mol) degrades down to <1 kg/mol and produces up to 23 mol % benzoyl products. A series of mechanistic studies showed that chlorine radicals promoted the degradation via hydrogen-atom abstraction. Commercial polystyrene degrades efficiently in our method, showing the compatibility of our system with polymer fillers. Finally, we demonstrated the potential of scaling up our approach in a photoflow process to convert gram quantities of PS to benzoic acid.

Despite the prevalence of alcohols and carboxylic acids as functional groups in organic molecules and the potential to serve as radical precursors, C−O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen-centered nucleophile. We show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H atom trapping to afford the deoxygenated products. Using the same method, we demonstrate access to synthetically versatile acyl radicals, which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge C−O, C−N, and C−C bonds in a single step.

Cationic polymerizations provide a valuable strategy for preparing macromolecules with excellent control but are inherently sensitive to impurities and commonly require rigorous reagent purification, low temperatures, and strictly anhydrous reaction conditions. By using pentacarbomethoxycyclopentadiene (PCCP) as the single-component initiating organic acid, we found that a diverse library of vinyl ethers can be controllably polymerized under ambient conditions. Additionally, excellent chain-end fidelity is maintained even without rigorous monomer purification. We hypothesize that a tight ion complex between the PCCP anion and the oxocarbenium ion chain end prevents chain-transfer events and enables a polymerization with living characteristics. Furthermore, terminating the polymerization with functional nucleophiles allows for chain-end functionalization in high yields.