James M. Eagan

Catalytic processes developed for petroleum refining, such as bifunctional hydrocracking, can be adopted to chemically recycle plastic polymers. In these reactions, polymer substrates often exhibit distinct kinetics from small molecules with identical chemical structures, emphasizing that the macromolecular behavior of polymer chains beyond local bonding modulates the reactivity. Here, we report the direct measurement of the dynamics of polymer chains at a model catalytic interface, using quasielastic neutron scattering (QENS). Three polypropylenes (PPs) of varying chain lengths and tacticities were studied. In all cases, polymer–catalyst interaction leads to the loss of bulk melting behavior, and segmental dynamics of PP chains can be described by continuous translational diffusion. A lower activation barrier and less favored entropy change at the transition state were observed at the catalytic interface relative to bulk melts, leading to reduced segmental diffusivity at reaction temperatures. The interfacial dynamics are faster for isotactic PP than for atactic PP. This difference is absent in the melt and rationalizes the higher reactivity of isotactic PP in diffusion-limited hydrocracking. This work pioneers the use of H-sensitive neutron-based techniques to probe the consequential macromolecular behaviors of reacting polymer chains at catalytic interfaces. The integration of such novel fundamental knowledge into bonding-level chemical kinetics can transform the understanding of catalytic polymer recycling reactions into a holistic framework, enabling the accurate explanation and prediction of phenomena not accounted for by traditional kinetic approaches.

A self-cross-linking polyisobutylene thiol (PIB thiol) was developed in this work from brominated isobutylene-co-para methylstyrene (BIMSM rubber). Nucleophilic substitution of BIMSM benzylic bromides using sulfur-based nucleophiles yields a shelf-stable intermediate PIB xanthate, which can be readily cleaved to produce thiol-grafted PIB. The PIB thiols oxidatively dimerize at elevated temperatures to yield a cross-linked network, reinforced solely through disulfide linkages. In the absence of accelerators, elemental sulfur, and other additives, this “traceless vulcanization” affords networks with up to 99% gel fractions and mechanical properties that can reach up to 1000 kPa in tensile strength, 1200% elongation, and shape recovery. Rheological analysis and cross-link density characterization provided insights into the reinforcement nature of a purely disulfide network in butyl rubbers with high creep resistance, along with low tan(δ) values across a wide range of temperatures and test frequencies.

Plastics entering composting systems are frequently found as fragments in finished compost, yet the mechanisms controlling their degradation and persistence remain unclear. In this study, food waste amended with virgin, 30-day UV-weathered, and 30-day sunlight-weathered polyethylene (PE) and poly(methyl methacrylate) (PMMA) microbeads was treated under aerobic and hyperthermophilic composting conditions. PE showed increased surface oxidation after both composting conditions, with the carbonyl index increasing from 3.6–16.6 in virgin to 12.2–25.1 in UV-weathered and 15.0–21.3 in sunlight-weathered beads. This oxidation corresponded with a decreased C/O ratio due to the formation of carbonyl and ester/carboxyl groups. Composting increased crack density on PE surfaces without altering molecular weight, indicating surface-limited degradation. In contrast, PMMA showed a 44–71% decrease in molecular weight after weathering, but no additional molecular weight reduction occurred during composting of weathered PMMA beads. After exposure to both composting conditions, PMMA showed increased thermal stability, whereas PE showed decreased thermal stability. Degradation rates were 6.2–19.5 μm yr–1 for PE and 5.9–33.9 μm yr–1 for PMMA, with estimated degradation times of 8.6–26.9 and 5.8–41.9 years, respectively. A field study showed that surface oxidation and crack density of PE, PP, PS, and PET correlated with compost maturity, likely due to prolonged exposure to dynamic composting conditions. These findings reveal plastic degradation pathways in compost and enable the prediction of their long-term environmental fate.

Highly branched polyethylenes (HBPEs) synthesized via α-diimine nickel catalysis exhibit excellent thermoplastic elasticity due to the unique combination of long and short branching structures. It is, however, challenging to analyze the crystalline structure, crystallinity, and crystal size distribution of HBPEs due to their low crystallinity. Therefore, the relationship between the branching structure, solid structure, and mechanical properties has not been established. In this work, we provide a detailed structural characterization of various HBPEs by using solid-state 13C NMR spectroscopy combined with magnetic relaxation measurements. The combination of two 13C spin–lattice relaxation methods quantitatively analyzes the crystallinity, as well as size distributions of both the orthorhombic and monoclinic phases. By quantitatively comparing the detailed branching microstructures with crystallinity, it is established that HBPEs with long chain branching (LCB < 12b/1000C) and short-chain branching (SCB < 85 b/1000C) exhibit semicrystalline features. Furthermore, it was found that high fractions of small crystallites relative to the large ones, rather than crystallinity, lead to excellent strain recovery behavior. In conclusion, solid structures, including crystallinity, polymorph, and crystalline size distribution, govern the unique thermoplastic elasticity of HBPEs. This research provides guidance for designing branching microstructures for tunable solid structures and the mechanical properties of HBPEs.

The catalytic conversion of carbon dioxide into polymers via high-energy comonomers offers a sustainable, low-cost, and low-emission approach to developing conveniently manufactured high-performance materials without competing for land use or food resources. We present the synthesis of poly(amidoamine) polymers stoichiometrically derived from carbon dioxide, butadiene, and amines displaying useful mechanical properties (tensile strength, 43 MPa; Young’s modulus, 840 MPa; and flexural modulus, 2.6 GPa). The low viscosity precursors (20 centipoise at 25°C) are applicable to producing carbon fiber reinforced polymers with fiber wetting and rapid network formation (16 min at 150°C). This work reveals that the reactivity of the internal hydrogen bonding catalyzes the ring-opening polymerization, and the intramolecular alcohol moiety promotes chemical recyclability to the monomers under acidic conditions, allowing the carbon fibers to be recovered with <1.0 wt % difference and reused in the manufacturing of recycled composites.

Hydrocracking is a promising route for the chemical recycling of polyolefins (PO), converting them into short hydrocarbons over bifunctional catalysts with metal sites for hydrogenation and dehydrogenation, and Brønsted acid sites (BAS) for isomerization and C-C bond cleavage. However, PO feedstocks containing polyvinyl chloride (PVC) can release chlorine (Cl) under reaction conditions, deactivating conventional noble metal/zeolite catalysts. Moreover, the lack of site intimacy and the presence of micropores within conventional catalysts create challenges around the transport of high-molecular-weight, sterically encumbered polymer intermediates. Here, we report tungsten carbides (W_xC) as a novel type of bifunctional catalysts that address these challenges. W/W₂C phases on W_xC offer "metal" sites, and -OH on WO_x species introduces BAS in close proximity. The "metal":BAS ratio can be tuned through carburization temperature, leading to a volcano-shaped activity trend reflecting the requirement for metal-BAS balance. Kinetic data demonstrate that each PO chain undergoes sequential cleavage, while trends in cracking ideality and selectivity follow those in short-alkane hydrocracking. On the per-BAS basis, W_xC is more efficient than conventional bifunctional catalysts by more than an order of magnitude, due to enhanced polymer transport. They maintain or show increased activity with 10 wt % PVC in the substrate. This work establishes transition-metal carbides as earth-abundant bifunctional catalysts with unique site proximity and heteroatom compatibility. These features, along with the broad structure space for rational tuning, make them promising options to tackle specific challenges that polymer feedstocks present in hydrocracking.

The mechanical properties of mixed plastics can be enhanced by block copolymer compatibilizer additives. Here we report a series of semi-crystalline/semi-crystalline linear multiblock copolymers of LLDPE and PP, the two most abundant plastics, from a non-living shuffling polymerization. Containing up to 13 individual blocks of PE and PP randomly arranged, the multiblock connectivity, crystallinity, and morphology are characterized with a combination of NMR, DSC, X-ray scattering, microscopy, and theoretical models. We show these semi-crystalline products compatibilize and toughen blends of the two most abundant plastics with an enhancement of tensile modulus. Due to the highly segmented nature of the multiblock copolymers, the crystalline morphology exhibits minimal phase separation and imbibes the amorphous chains in commercial polymer interfaces into the semi-crystalline block copolymer phase by transmission electron microscopy. The work provides access to compatibilizer designs that implement a combination of tie-chain, trapped entanglement, and co-crystallization reinforcement mechanisms for toughening post-consumer blends.

A CO ₂ -derived PCHC vitrimer cured with zinc stearate enables rapid reprocessing, efficient glycolysis, and >97% conversion to ethylene carbonate. When applied to CFRPs, it allows complete resin valorisation and recovery of pristine fibres.

The catalytic conversion of carbon dioxide into polymers via high-energy comonomers offers a sustainable, low-cost, and low-emission approach for developing conveniently manufactured high-performance materials without competing for land-use or food resources. We present the synthesis of poly(amidoamine) polymers stoichiometrically derived from carbon dioxide, butadiene, and amines displaying useful mechanical properties (tensile strength 43 MPa, Young’s modulus 840 MPa, and flexural modulus 2.8 GPa). The low viscosity precursors are applicable to producing carbon fiber reinforced polymers with fiber wetting and rapid network formation (16 minutes at 150°C). This work reveals that internal hydrogen-bonding catalyzes the ring-opening polymerization, and the intramolecular alcohol moiety promotes chemical recyclability in acidic conditions, allowing fiber recovery with <1.0 wt % difference from virgin fiber and monomer in 72% yield.