Nonalternating Ni(II)-catalyzed copolymerization of ethylene and carbon monoxide enables access to keto-functionalized polyethylenes but is challenged by strong CO binding and chain-growth inhibition by incorporated ketone groups. Here, we report a bimetallic bis(phosphine phenolate) Ni(II) complex based on a BINOL framework with a P-bound 2 ',6 '-dimethoxy-1,1 '-biphenyl substituent, alongside a monometallic analogue. Both complexes are active catalysts, producing high-molecular-weight keto-polyethylenes with predominantly isolated ketone units. Notably, the bimetallic system can afford higher molecular weights under identical conditions, which we attribute tentatively to the increased steric bulk provided by the second metal center.

ABSTRACT In‐chain functional groups can reduce the environmental impact of polyethylene waste and enhance its recyclability. A significant advance was the realization of the long‐sought catalytic copolymerization of carbon monoxide with ethylene in a non‐alternating manner, providing keto‐polyethylene materials with low densities of photodegradable keto groups in the chain. Despite this breakthrough, the state‐of‐the‐art catalysts’ limited carbon monoxide tolerance is a hurdle in further developing more sustainable polyethylenes. Here we show how these fundamental issues can be addressed by implementation of attractive Ni···O interactions in novel as well as state‐of‐the‐art neutral nickel catalyst motifs. Incorporation of P ‐bound 2,6‐diphenoxyphenyl moieties into both phosphine‐imidate and phosphine‐phenolate ligand frameworks provides highly active and robust catalysts that generate keto‐polyethylenes not accessible to date. Theoretical calculations reveal that Ni···O interactions lower cis/trans isomerization barriers of coordinated ethylene, thereby driving ethylene insertion along the desired non‐alternating pathway. At the same time, steric constraint raises the energy barriers for carbon monoxide insertion and reductive elimination, effectively suppressing undesired extensive carbon monoxide insertion and catalyst deactivation. The concept uncovered enables operating conditions, productivities and in‐chain functional group concentrations not possible with existing catalysts, and provides perspectives for putting much needed environmentally benign polyolefins into practice.

Polyethylene mimics such as long-spaced aliphatic polyesters (LSAPE) are biodegradable and recyclable in a close-loop path. They are viewed as possible alternatives to classical polyethylenes that are inert and difficult to recycle. However, inclusion of the ester groups as crystalline layers inside the core crystalline regions bestow LSAPE features in their crystal structures that differ from the simple orthorhombic packing of linear polyethylene. In this work, we have determined the crystal structures of long-spaced aliphatic polyesters PE-X,18 (-[-(CH2) X -OCO-(CH2)16-COO-] n -; X = 2, 3, 4 or 6) and polyester PE-2,13 (-[-(CH2)2-OCO-(CH2)11-COO-] n -) by analyzing their 2D-wide-angle X-ray fiber diffraction data. The chain conformation is different depending on the odd or even number of X. Even-X congeners take a vertically oriented and almost straight chain form with local kinks (gauche conformers) at the CH2-O bonds, while the odd-X member packs into large and long zigzag arms of the almost fully extended 16 methylene segments, also with gauche bonds at the CH2-O junction. The methylene segments are packed closely in the sublattice similarly to the herringbone-type structure of orthorhombic polyethylene. This packing is supported by IR spectral observations of the correlation splitting and by adherence to the n-alkane dispersion curve of the series of progression bands in the frequency region of rocking-twisting CH2 modes. The a sub and b sub values of the subcell structure, composed of methylene zigzag segments, are very close to those of the orthorhombic-type of the linear polyethylene crystal.

While x-ray scattering and broadband dielectric spectroscopy (BDS) experiments are routinely performed in vacuum and under controlled humidity on bulk samples, in situ measurements of thin films in non-aqueous solvent vapor environments introduce additional requirements. Two controlled environmental chambers for performing grazing incidence x-ray scattering and BDS address this critical need for studying thin films in either aqueous or organic atmospheres. Both chambers enable temperature-controlled measurements under ambient conditions, flowing gas or solvent vapor, or partial pressures generated by solvent reservoirs. In situ control of temperature is achieved by attaching to an external temperature controller. To facilitate grazing incidence small- and wide-angle x-ray scattering and x-ray reflectivity, the environmental chamber for grazing incidence x-ray scattering has exit angles of 2θ = 38° and 51° in the horizontal and vertical directions, respectively. Low x-ray attenuation (∼ 10%) is achieved by using Kapton windows, and the chamber is sealed to enable use in evacuated x-ray scattering systems such as the Xenocs Xeuss 2.0. The broadband dielectric spectroscopy environmental chamber measures dipole dynamics and ionic conductivities of materials on interdigitated electrodes. Cord grip feedthroughs eliminate additional capacitance from the sample chamber and make the environmental chamber broadly compatible with electrochemical impedance spectrometers. The utility of these chambers is demonstrated on three polymeric systems with various film thicknesses, morphologies, and solvents.

The plastisphere is a unique ecosystem with microbes colonizing and potentially degrading plastic debris in the environment, provided that the polymers are enzymatically accessible as substrates to drive microbial growth. It also harbors an unusually high occurrence of antibiotic resistance genes, suggesting plastic debris as a potential vector for antibiotic-resistant microorganisms. In this study, we investigated microbial communities in forest soil degrading an emerging type of bioplastics, aliphatic long-chain polyesters (LCAPs). Sequencing analysis revealed a family-VIII esterase strongly associated with LCAP depolymerization that showed high structural similarity to type C β-lactamases. Structural modeling and substrate docking analysis indicated catalytically favorable binding of both LCAP and β-lactam antibiotics. Furthermore, the active site appeared to be located in a large, wide-open groove, rather than in a tunnel, resulting in a protein with a striking "pac-man"-like structure. Heterologous expression and in vitro activity testing confirmed its dual functionality as plastic depolymerase and β-lactam hydrolase. Sequence analysis indicated the enzyme as membrane-associated lipoprotein likely to be directed to the outer membrane. The membrane anchoring of the enzyme may offer striking microbial-ecological benefits, by preventing enzyme loss especially in aqueous environments, by increased catalytic efficiency through high enzyme concentration at the cell-plastic interface, and by spatially linking catalysis with membrane transport, thereby limiting monomer loss to non-producing plastisphere-community members (cheaters). Hence, our study highlighted a plastic depolymerizing enzyme with a striking substrate spectrum, bridging plastics and antibiotics degradation, and provides intriguing perspectives for understanding the microbial physiology, ecology, and evolution of (bio)plastic degradation in the environment.

Phosphinephenol esters react with Ni0 to afford otherwise difficult to access NiII-alkyl complexes. The reaction proceeds efficiently and cleanly by coordination of phosphine to the Ni0, which directs an intramolecular oxidative addition into the C(acyl)-O bond followed by rapid carbon monoxide elimination. The potential of this mild preparative pathway was demonstrated by the synthesis of a higher NiII-n-alkyl complex, and of a five-membered chelate that is the key intermediate in the nonalternating copolymerization of ethylene and carbon monoxide, as well as its 13C-labeled analog. Further, the title reaction can regenerate active polymerization catalyst after CO-induced deactivation under pressure reactor conditions, highlighting its broader utility. This shows the directed oxidative addition-decarbonylation of phenolesters provides a broad platform to access catalytically relevant Ni alkyl complexes.

The addition of polar solvents is known to increase the ionic conductivity of ion-containing polymers toward relevant values. For nanostructured polymers, ionic conductivity can also be improved by aligning the nanostructures to eliminate discontinuities in conduction pathways associated with misorientations of the conducting domains, grain boundaries, and defects. Here, we report improvements in ion conductivity with both solvent swelling and alignment by studying thin films of a precise amphiphilic multiblock copolymer ionomer. Samples were characterized under saturated solvent vapor by grazing incidence X-ray scattering and broadband dielectric spectroscopy using interdigitated electrodes. The layered ionic assemblies remain parallel to the substrate upon swelling the polar sublayers with selective solvents (λ = 2-2.5 solvent molecules per sulfonate). Relative to isotropic and solvent-free bulk samples, the in-plane ionic conductivities increase significantly due to alignment and solvent swelling with propylene carbonate, γ-butyrolactone, dimethyl carbonate, or diglyme. Interestingly, the ionic conductivity of an isotropic bulk sample swollen with propylene carbonate (λ = 1) is ∼ 1.5 orders of magnitude greater than an aligned thin film swollen with propylene carbonate (λ = 2.4). This result suggests that grain boundaries and defects in bulk samples of this alternating multiblock copolymer are preferentially swollen with solvent, providing pathways for rapid ion transport, and indicates routes to further improve ionic conductivity in solvent-swollen nanostructured ionomers.

These concluding remarks summarize the Faraday Discussion meeting titled "Polymerisation and depolymerisation chemistry: the second century" held in Oxford, UK in September 2025.

The recent achievement of a nonalternating ethylene/carbon monoxide (CO) copolymerization was a long-sought breakthrough. Their in-chain keto functional groups endow the resulting polyethylenes (keto-PEs) with photodegradability. To date, only two types of catalysts, based on long-known structural motifs, are capable of this challenging copolymerization to keto-PE materials, raising the question whether the reaction is restricted to this narrow scope. Here, we report a diverse range of neutral Ni(II) complexes provides access to keto-PEs, including a phosphine imidate Ni(II) catalyst that is competitive with state-of-the-art catalysts and a N-heterocyclic-carbene (NHC) phenolate Ni(II) catalyst with exceptional preference for ethylene vs CO incorporation. Density functional theory (DFT) calculations rationalize the observed selectivity for nonalternating and alternating chain growth from the individual catalysts' activation barrier differences ΔΔG‡ and identify the strong trans-effect of the [NHC,O]-ligand and its high steric hindrance as origins of the desirable exceptionally low preference for CO incorporation.

Microorganisms in the plastisphere are associated with plastic degradation, as well as with an unusually high occurrence of antibiotic resistance genes (ARGs), suggesting plastic debris as a potential vector for antibiotic-resistant microorganisms. In this study, we investigated microbial communities associated with the degradation of aliphatic long-chain polyester (LCAP) bioplastics in forest soil. Sequencing analysis revealed a family VIII esterase with structural similarity to type C β-lactamases. Structural modeling and substrate docking analysis indicated catalytically favorable binding of both LCAP and β-lactam antibiotics. Heterologous expression and in-vitro activity testing confirmed its dual functionality as plastic depolymerase and β-lactam hydrolase. Sequence-based predictions identify the enzyme as a membrane-associated lipoprotein, with suggested further secretion via outer-membrane vesicles (OMVs), offering potential ecological benefits in competitive plastisphere environments. These findings highlight an enzyme with a rare substrate spectrum, bridging plastic and antibiotics degradation and suggesting an intriguing biochemical connection that warrants further investigation of microbial evolution in the plastisphere and its potential implications for the spread of antibiotic resistance. ### Competing Interest Statement The authors have declared no competing interest. Carl Zeiss Foundation, https://ror.org/03ng4kg22, CZS Perspektiven project INPEW University of Konstanz, professorial start-up grant awareded to D.S.

Biodegradable plastics are an important component for achieving a circular polymer economy. To be considered biodegradable at the regulatory level, plastics must pass standardized tests, for example under industrial composting conditions at 58 °C (ISO 14855-1). Although such tests are frequently applied, little is known about the microorganisms catalyzing these degradation processes. Recently, bioplastics with properties similar to polyethylene, Long-Chain Aliphatic Polyesters (LCAP), for example polyester 1,18-octadecanediol-alt-1,18-octadecanedioic acid (abbreviated PE-18,18), were shown to biodegrade under industrial composting conditions. In this work, we analyzed the microbial communities that had developed in the compost treatments at the end of the biodegradation test for three different LCAPs (PE-18,18, PE-12,12 and PE-2,18) relative to the untreated controls, via amplicon-sequencing of bacterial 16S and fungal ITS2 rDNA. This revealed significant treatment-induced shifts in the bacterial communities (p < 0.05), with Pseudonocardia and Thermomonospora ASVs enriched in all LCAP-treated samples compared to the controls (p ≤ 0.0001), while no pronounced shifts were observed for the fungal community. Thermomonospora sequences showed high similarity to T. curvata DSM43183, which encodes the known polyester hydrolase Tcur1278, and the presence of gene tcur1278 was confirmed in LCAP-treated samples via PCR. Enzyme assays with heterologously expressed and partially purified Tcur1278 demonstrated its activity on PE-2,18 LCAP, releasing up to 230 μmol of soluble monomers over 48 h at 50 °C. Hence, our study implicated Thermomonospora species in LCAP degradation during thermophilic composting, based on taxonomic enrichment, and provided evidence linking the detected phylotypes to Tcur1278, the first bacterial enzyme demonstrated to depolymerize LCAP. It thereby is the first evidence for an ecological relevance of Tcur1278-encoding Thermomonospora phylotypes for bioplastic degradation in situ.

Herein, we use three series of aliphatic polyesters, designated as PE-X,Y-where X and Y denote the number of carbon atoms in the diol and diacid, respectively-as model systems to ascertain the molecular and structural factors that govern the manifestation of minima in the temperature dependence of the isothermal crystallization rate. We demonstrate that a required structural factor to observe rate minima is the formation of layered crystallites (lamellar crystals with ester-layered crystalline regions). Up to X congruent to Y/2, polyesters of series PE-X,18 develop layered crystals, and many display up to three rate minima. Unlayered polyesters such as PE-10,18 do not show rate minima. Such correspondence supports the notion of frustration or "self-poisoning" to explain the retardation of the rate observed in a narrow range of temperatures at the transition between quantized crystal thicknesses, thus indicating that the layer is a marker to detect rate anomalies that may point out specifics of polymer crystal growth. The aliphatic CH2 length between esters is an additional factor limiting the manifestation of rate minima. Despite forming layered crystals with quantized crystal thicknesses, as documented by X-ray measurements, the lack of rate minima in the even-spaced polyesters PE-X,12 is explained as a fast thickening at the transition between quantized crystal thicknesses. Furthermore, we also point out that the rate minima observed at temperatures close to the glass transition occur at the convergence of bimodal crystallization kinetics that differs between heterogeneous (high temperature) and homogeneous (low temperature) nucleation modes. Polymorphism, which is observed in some polyesters with a short odd-spaced diol, is uncorrelated with the observed rate minima.

Polyethylene-like aliphatic polyesters are promising biodegradable polymers; however, their conformational and supramolecular structures are not well understood. Here, we used solid-state nuclear magnetic resonance (NMR) to investigate three synthetically accessible polyesters made from doubly 13C-labeled ethylene diol units and unlabeled dicarboxylic acids of 12-, 18-, and 48-carbon length (PE-2,12 to PE-2,48). Signals of abundant gauche OCH2-CH2O conformers observed in all samples are spectrally resolved from the sharp peak of crystalline anti OCH2-CH2O segments in PE-2,12 and PE-2,18. Layers of disordered and immobilized gauche OCH2-CH2O units at the crystal-amorphous interfaces are present in all samples. PE-2,12 and PE-2,18 additionally contain mobile amorphous and crystalline gauche OCH2-CH2O units. The unexpected crystalline gauche conformation deduced from the chemical shift and slow 13C spin-lattice relaxation was proved by fast decay in centerband-only detection of exchange (CODEX) NMR. The location of these gauche OCH2 groups deep inside the crystallites was confirmed by 1H spin diffusion from the amorphous layers. Crystalline gauche moieties, observed in three different samples of PE-2,12, account for about 1/3 of its crystalline OCH2 groups. Based on quantitative NMR and spin diffusion, specific models of the layered supramolecular structures were developed, with gauche OCH2 in interfacial layers at the crystal surfaces. While PE-2,18 and PE-2,12 contain two or three anti diol/diester layers within each crystallite, most OCH2 groups in PE-2,48 are immobilized at the interfaces, and mobile gauche or crystalline anti OCH2 units are insignificant. Thus, PE-2,48 contains all-polyethylene crystalline lamellae capped by diol/diester interfacial layers, indicating chemical control of the crystallite thickness.

Endowing polyethylenes with photodegradability via incorporation of low densities of in-chain keto units could reduce the problematic environmental persistency of littered polymer waste. A breakthrough enabling such materials is the recent finding of nickel catalyzed nonalternating copolymerization of ethylene-carbon monoxide. We reveal irreversible catalyst deactivation pathways operative in this reaction. Reductive elimination of the common phosphinephenolate Ni(II) motif occurs with the acyl intermediates formed upon incorporation of carbon monoxide into the growing chain, as observed by low temperature NMR spectroscopy and single crystal X-ray crystallography of the isolated product. Further, we show that such decomposition pathways are generally relevant during ethylene-carbon monoxide copolymerizations under pressure reactor conditions. These findings guide the development of more stable and productive polymerization catalysts to enable the production of environmentally benign polyethylenes.

Mechanochemical conversion of polyethylene (PE) and polypropylene was shown to produce monomers and is thus interesting for chemical polymer recycling. As these polymers make up more than 50% of the worldwide polymer production, studying their conversion during ball milling is especially relevant. However, fundamental knowledge on the effect of crystallinity, degree of polymerization, entanglement and temperature on the conversion is lacking due to the difficulty in producing polyolefins with controlled chain length and dispersity. Here we synthesize PE by a controlled chain growth polymerization and study its degradation during ball milling at cryogenic conditions, at room temperature (RT), with and without air, and using either steel or zirconia grinding spheres. Resulting molecular weight distributions are fitted using a statistical chain cleavage model suggesting a statistical Gaussian distribution of chain cleavage probability around the middle of the chain. This is likely because if the chains are fixed in an entanglement or crystal at two points, they cannot slip out and force can act on them leading to cleavage. That the chain is fixed at both sides of a possible cleavage location is most likely if the cleavage location is in the center of the chain. Chain cleavage is also promoted when entangled domains exist that link crystalline regions. A micelle grown single crystal ultrahigh molecular weight PE without entanglements was milled and its molar mass decreased much less compared to the same sample that was annealed to create entanglements. However, in contrast to previous studies and common expectations, the initial molar mass of the polymer, the degree of crystallinity and the brittleness of the sample did not have a measurable influence on chain cleavage. While the decrease in molar mass was faster at cryogenic conditions compared to RT, nuclear magnetic resonance (NMR) results suggest that this is due to a suppression of radical recombination rather than the higher brittleness of the material below its glass transition temperature (∼-120 °C). Similarly, the number of permanent scissions increased by up to 2.6 times under air compared to nitrogen atmosphere, especially in combination with steel milling spheres. NMR spectra of the milled samples suggest that the reaction of mechanochemically formed chains with air suppresses recombination.

Pd(II) phosphinosulfonate catalysts were employed in the nonalternating copolymerization of ethylene and carbon monoxide to produce keto-polyethylenes with high-density polyethylene-like materials properties. The different reactivities of the two monomers were addressed with a customized reactor setup that allows the feeding of ethylene and CO at very different feed ratios and automatic repressurization to replenish consumed monomers upon reaching a pressure threshold. Four literature-known catalysts were screened and the keto group microstructure of the resulting keto-PEs aligned well with the activation free energy differences (ΔΔG‡) of the alternating and nonalternating pathways, calculated via density functional theory. Pd-2 with a 2',6'-dimethoxy-1,1'-biphenyl-substituted phosphine motif was the most active catalyst, yielding copolymers with the highest molecular weight (around 30-40 kg mol-1). Consequently, Pd-2 was subjected to further optimization of the E/CO copolymerization to obtain HDPE-like materials. Tensile-testing specimens of keto-PEs with 0.5 and 1.4 mol % of keto groups were obtained via melt pressing and exhibited mechanical properties on par with the HDPE reference material.

We report the self-assembly behavior of strictly alternating multiblock copolymers with a sulfonated polar block and various alkyl blocks. The alkyl blocks are linear with x carbons (PESMx), a mixture of linear and sterically hindered fatty acid dimer blocks (PESNax-20%Pripol), or sterically hindered with an isopropyl group (PESMx-iPr). These new multiblock copolymers have blocks with <= 20 backbone bonds and a large interaction parameter. Polymers with 20% Pripol blocks exhibit reduced crystallinity relative to the multiblock copolymers with linear alkyl blocks, while polymers with 100% iPr groups are fully amorphous. While PESMx polymers form the double gyroid morphology above the melting temperature over a broad range of polar volume fractions, the new PESNax-20%Pripol and PESMx-iPr multiblock copolymers exclusively form hexagonal morphologies in the melt. We attribute the absence of a stable double gyroid morphology to prohibitively high degrees of chain stretching of the alkyl blocks. This study highlights the importance of packing frustration in the majority domain on the self-assembly behavior in high-chi, low-N multiblock copolymers.

Sourcing commodity polymers from sustainable alternative feedstocks, such as those derived from plastic waste or biobased resources, is a promising approach to alleviate the reliance on finite fossil fuel stocks for the production of virgin plastics. Linear aliphatic dicarboxylic acids of multiple chain lengths can be obtained from polyethylene (PE) waste, and their use in the synthesis of aliphatic polyesters has recently been demonstrated. To improve the materials' properties of polyesters derived from multiple chain-length dicarboxylates, we herein combined this feedstock with terephthalate as an aromatic monomer unit to yield aliphatic-aromatic copolyesters. We established structure-property relationships for copolyesters derived from aliphatic dicarboxylates of multiple chain lengths (C4-C20) as a model for catalytic oxidation products of PE waste, or from 1,18-octadecanedioate as reference materials for polyesters from single, long chain length dicarboxylates. Thermal properties and solid-state structures were dominated by the ratio of aliphatic to aromatic monomer units rather than the identity of the aliphatic dicarboxylate or diol components. We demonstrated upscaling of the copolyester synthesis, as well as processability and mechanical properties of a multiple chain length copolyester, which showed comparable properties to the commercial polybutylene adipate-co-terephthalate. Finally, we showed an alternative production via catalytic transesterification and thus postmodification of premade polyesters, including postconsumer polyethylene terephthalate, as model waste sources.