Megan R. Hill

Effective Recycling Pathways of Commodity Polymers Enabled by Mechanoradical Capture 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.

Very excited to share our recent article in JACS where we showed that we could capture mechanoradicals formed during polymer degradation and use them to grow polymers back to high MWs or prime them for depolymerization! pubs.acs.org/doi/10.1021/...

Be my colleague! Cal Poly San Luis Obispo is hiring two tenure-track positions for Fall 2026, chemical education and coatings technology.

Chen Ed: jobs.calpoly.edu/en-us/job/55...

Coatings: jobs.calpoly.edu/en-us/job/55...

Efficient super-reducing organic photoredox catalysis with proton-coupled electron transfer mitigated back electron transfer 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...

Congrats to Amreen and Arindam and the whole team on getting their work out in Science today!! www.science.org/doi/10.1126/...

Congrats Jill!!! 🎉

Congrats Jessica!! 👏

Influence of Dihydrophenazine Photoredox Catalyst Excited State Character and Reduction Potentials on Control in Organocatalyzed Atom Transfer Radical Polymerization 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.

Congrats to former SuPRCat-er and recent grad Katrina on her publication in ACS Catalysis! pubs.acs.org/doi/10.1021/...

It may not be cool or hip in some circles, but we legitimately do need a massive amount of people to run for office.

Flood the school boards, councils, county seats, state legislatures, Congress, etc.

Big changes at the top happen when the ground shifts at the bottom. And that can start now.

Breaking down Plexiglas with light Chlorine radicals unmake commercial polymethacrylates under mild conditions

On really sad lab days in grad school, I'd tell my labmates they were going to make a mistake, make a serendipitous discovery, and get a Science paper out of it.

For one chemist, that happened! An accidental discovery of a new way to recycle Plexiglas! 😍

via @bribarbu.bsky.social:
🧪⚗️ #chemsky

To do this & do it without any apparent input from longtime members (& to serve up an obnoxiously cutesy 404 page on top of it all) is very bad

I've been wondering when this would happen!

A version of the kermit vs darth kermit meme where good kermit tells the online academic that they should grade, while darth kermit tells them they should eat more pie.

Every academic right now

Such cool work!! Did the Stache lab just solve the plastic crisis?? 😅 can’t wait to see what’s next!

Tons of great insight about microplastics in this edition of @cenmag.bsky.social but this one I found particularly interesting.

Bioinspired, Carbohydrate-Containing Polymers Efficiently and Reversibly Sequester Heavy Metals 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...

Cool work by Cassandra Callmann & team in ACS Cent Sci reporting a sugar-like polymer that removes heavy metals from water by forming a recyclable precipitate. As proof-of-concept, the polymer removed Cd & Pb from river water spiked with these persistent contaminants pubs.acs.org/doi/10.1021/...

Photocatalytic low-temperature defluorination of PFASs - Nature 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...

There are two really cool #PFAS / #foreverchemicals degradation papers out in Nature today

In one, the authors show that powdered Teflon can be transformed into charcoal+fluoride with light+a catalyst+reducing reagent & some very important help from mainly KOH and Cs formate

This is bonkers cool:

Calling all polymer scientists! Let’s re-find each other as people continue to migrate over!

Please tag people in the comments and share! I’ll continue updating as we find more people. #polymers

go.bsky.app/AgjxzFa