Plastics pervade every aspect of modern life, yet effective mechanical recycling remains a major challenge. This is, in part, because of the mechanical forces that are involved in reprocessing, which break polymer chains and generate mechanoradicals, leading to a reduction in molecular weight and diminished material properties. This work introduces a robust strategy to capture and redirect these reactive intermediates, enabling value-preserving recycling pathways for widely used polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA). By employing ball milling to induce chain scission, we demonstrate that mechanoradicals can be trapped by bis(butyl trithiocarbonate), yielding polymers with trithiocarbonate (TTC) end groups. Polymers degraded via ball milling showed significant reduction in molecular weight, ≈90% lower than the pristine polymers. These low molecular weight, TTC-functionalized polymers then served as macroinitiators for light-mediated controlled polymerization or, in the case of PMMA, as mediators for depolymerization under mild conditions. Chain extension of the degraded materials led to restored or increased molecular weight compared to the pristine polymers. Shear oscillatory rheology experiments revealed a recovery of entangled polymer properties, as evidenced by the reappearance of the rubbery plateau. We further showed that this “capture-and-repair” strategy is compatible with multiple cycles of degradation and chain extension, achieving repeated molecular weight recovery over three cycles. Additionally, we found that ball milling alone lowers the thermal depolymerization temperature of PMMA, enabling up to ≈44% depolymerization at 220 °C. Together, these findings highlight mechanoradical capture as a promising strategy to both enhance circularity and improve overall performance of mechanically recycled plastics.

Photoredox catalysis driven by visible light has improved chemical synthesis by enabling milder reaction conditions and unlocking distinct reaction mechanisms. Despite the transformative impact, visib...

The development of N,N-diaryl dihydrophenazine organic photoredox catalysts (PCs) has enabled numerous examples of organocatalyzed atom transfer radical polymerization (O-ATRP) of methyl methacrylate (MMA) monomer to polymers with low dispersity (Đ < 1.30) and near-unity initiator efficiency (I* ∼ 100%), as well as small molecule synthesis. In this work, we investigate the influence of core substitution (CS) by alkyl, aryl, and heteroatom groups on singlet excited state reduction potential (ES1°*). We observe that a highly reducing ES1°* is in part a result of a locally excited (LE)-dominated hybridized local and charge transfer (HLCT) excited state in CS PCs, which is influenced by the identity of the core substituent. Additionally, the PCs that possess a LE-dominated HLCT character maintain a relatively oxidizing PC radical cation oxidation potential (E1/2) for deactivation in O-ATRP compared to fully LE PCs reported in prior work. For example, a thiophenol core substituted (heteroatom CS, HetCS) PC shows the most negative ES1°* (−2.07 V vs SCE), more LE character (Stokes shift = 124 nm), and has an oxidizing PC radical cation (E1/2 = 0.30 V vs SCE). The CS PCs with improved properties, including more negative ES1°*, perform best in O-ATRP of MMA with the HetCS PC showing the best control in both DMAc (Đ = 1.08, I* = 89%) and EtOAc (Đ = 1.06, I* = 97%). Additionally, the HetCS PC was found to mediate the controlled polymerization of n-butyl acrylate (n-BA) (Đ = 1.24, I* = 97%), which has remained challenging in O-ATRP without supplemental deactivation strategies. An aryl CS PC was found to have moderate control as low as 1 ppm PC, indicating facilitation of low PC loadings (Đ = 1.33, I* = 69%). The relationship between excited state character, ES1°*, and polymerization control observed in this work provides a foundation for increasing the utility of phenazine PCs across photoredox catalysis.

Chlorine radicals unmake commercial polymethacrylates under mild conditions

Water scarcity and heavy metal pollution are significant challenges in today’s industrialized world. Conventional heavy metal remediation methods are often inefficient and energy-intensive, and produc...

Photocatalysis at 40–60 °C is shown to be able to defluorinate perfluoroalkyl substances, known as ‘forever chemicals’, allowing the recycling of fluorine in polyfluoroalkyl and perfluoroalkyl substan...