Efficient and Robust Dynamic Crosslinking for Compatibilizing Immiscible Mixed Plastics through In Situ Generated Singlet Nitrenes

Creating a sustainable economy for plastics demands the exploration of new strategies for efficient management of mixed plastic waste. The inherent incompatibility of different plastics poses a major challenge in plastic mechanical recycling, resulting in phase-separated materials with inferior mechanical properties. Here, this study presents a robust and efficient dynamic crosslinking chemistry that effectively compatibilizes mixed plastics. Composed of aromatic sulfonyl azides, the dynamic crosslinker shows high thermal stability and generates singlet nitrene species in situ during solvent-free melt-extrusion, effectively promoting C─H insertion across diverse plastics. This new method demonstrates successful compatibilization of binary polymer blends and model mixed plastics, enhancing mechanical performance and improving phase morphology. It holds promise for managing mixed plastic waste, supporting a more sustainable lifecycle for plastics.

Diverse functional polyethylenes by catalytic amination

Functional polyethylenes possess valuable bulk and surface properties, but the limits of current synthetic methods narrow the range of accessible materials and prevent many envisioned applications. Instead, these materials are often used in composite films that are challenging to recycle. We report a Cu-catalyzed amination of polyethylenes to form mono- and bifunctional materials containing a series of polar groups and substituents. Designed catalysts with hydrophobic moieties enable the amination of linear and branched polyethylenes without chain scission or cross-linking, leading to polyethylenes with otherwise inaccessible combinations of functional groups and architectures. The resulting materials possess tunable bulk and surface properties, including toughness, adhesion to metal, paintability, and water solubility, which could unlock applications for functional polyethylenes and reduce the need for complex composites.

Tandem ROMP/Hydrogenation Approach to Hydroxy-Telechelic Linear Polyethylene

Hydroxy-telechelic polyalkenamers have long been synthesized using ring-opening metathesis polymerization (ROMP) in the presence of an acyclic olefin chain-transfer agent (CTA); however, this route typically requires protected diols in the CTA due to the challenge of alcohol-mediated degradation of ruthenium metathesis catalysts that can not only deactivate the catalysts, but also compromise the CTA. We demonstrate the synthesis and implementation of a new hydroxyl-containing CTA in which extended methylene spacers isolate the olefin and alcohol moieties to mitigate decomposition pathways. This CTA enabled the direct ROMP synthesis of hydroxy-telechelic polycyclooctene with controlled chain lengths dictated by the initial ratio of monomer to CTA. The elimination of protection/deprotection steps resulted in improved atom economy. Subsequent hydrogenation of the backbone olefins was performed by a one-pot, catalytic approach employing the ruthenium complex used for the initial ROMP. The resultant approach is a streamlined, atom-economic, and low-waste route to hydroxy-telechelic linear polyethylene that uses a green solvent, succeeds with miniscule quantities of catalyst (0.005 mol %), and requires no additional purification steps.

The challenges of controlling polymer synthesis at the molecular and macromolecular level

In this Perspective, we outline advances and challenges in controlling the structure of polymers at various size regimes in the context of structural features such as molecular weight distribution, end groups, architecture, composition and sequence.

The post-modification of polyolefins with emerging synthetic methods

This Perspective highlights the present state of polyolefin post-modification research, especially concerning recently developed C–H functionalization chemistry. Remaining challenges and emerging strategies within the field have also been discussed.

A direct functionalization of polyolefins for blend compatibilization by an insertion of 1,1-bis(phenylsulfonyl)ethylene (BPSE)

A mild post-modification of polyethylene (PE) & polypropylene (PP) to insert phenylsulfonyl groups is reported, the modified samples demonstrated to act as blend compatibilizers.

Functionalization of PP with Sulfonyl Azide through Reactive Processing

The functionalization of polypropylene (PP) by 4-carboxybenzene sulfonyl azide (CBSA) was investigated in a batch mixer and the reaction was monitored through FTIR, 1H-NMR and XPS spectroscopy. The degree of grafting was found to increase initially with azide feed content and subsequently to level off at azide concentrations of 2 wt.%. Experiments performed at different reaction temperatures showed that a maximum degree of grafting was obtained around 190°C. The linear viscoelastic properties the functionalized PPs were also evaluated by oscillatory shear measurements and were found to correlate with the grafting degree results. Finally, the adhesive properties of the functionalized PPs were evaluated through peel tests on aluminum substrates. The peel strength increased with the degree of grafting and it was found to be significantly higher for purified samples than for non-purified ones. Finally, it was demonstrated that the cooling rate of the PP/aluminum laminate specimens had a major effect on the peel strength.

CROSS-LINKING OF SATURATED ELASTOMERS WITH DI-AZIDES. PART II: MECHANISTIC STUDY

In the first part, one di-sulfonyl azide: 1,3BDSA, and two di-azidoformates: GDAF and 4,4′DAF, were selected and extensively investigated as curing agents for EP(D)M rubbers. Although the mechanical properties of the vulcanizates vary significantly with the particular di-azide used, all of them act as effective curing agents compared to a peroxide/coagent curing system. To explain the differences in properties as well as to obtain a deeper understanding of the reaction mechanism, model compound experiments are performed with 4-methylheptane as substitute for the saturated ethylene–propylene copolymer rubber backbone. Using gas chromatography/mass spectrometry and high performance liquid chromatography/mass spectrometry as analytical tools, a basic understanding of the reaction mechanisms between sulfonyl azide and azidoformate functionalities and saturated hydrocarbons is obtained.

CROSSLINKING OF SATURATED ELASTOMERS WITH DIAZIDES. PART I: MECHANICAL PROPERTIES OF VULCANIZATES

For vulcanization of fully saturated elastomers peroxide/coagent systems are commonly applied. Problems encountered with peroxides however, are reduced efficiency, especially in the presence of plasticizing oils, and unwanted side reactions. In this paper diazides are presented as alternatives to peroxide vulcanization systems, particularly in combination with the use of plasticizing oils. The performance of three diazides; tri(ethylene glycol)-di(azidoformate) (GDAF), 4,4′-isopropylidenediphenyl azidoformate (4,4′DAF) and 1,3-benzenedisulfonyl azide (1,3BDSA) is investigated. For the evaluation of the practical product performance, carbon black filled and oil extended compounds of EPM and EPDM-rubbers are used. It is also investigated how the presence of carbon black and plasticizing oil influences the diazide reaction kinetics.