Chemically Recyclable Polyethylene-like Sulfur-Containing Plastics from Sustainable Feedstocks

Multicomponent Polymerizations Provide Sustainable Sulfur (Selenium)-Containing Polyesters

ConspectusWith the rapid development of the polymer industry, the contradiction between synthetic polymers and the sustainable development of human society is becoming more and more prominent. The advancement of degradable plastics greatly contributes to the sustainability of our society. Synthetic polymers containing precisely placed in-chain ester groups are expected to be degradable in a controlled manner. Their potential as environmentally benign plastics is significant. For this purpose, there is a clear need for their improved performance. Incorporating sulfur functional groups into polyesters can improve the diverse crucial properties of their counterparts. However, there is a lack of related high-efficiency polymer synthesis methods.In response to this issue, we designed a series of multicomponent polymerization methods for the synthesis of a library of degradable polyesters with tunable structure and properties. This Account summarizes our recent efforts to discover the polymerization approach. The method uses readily available monomers including diols, diamines, H2O, diacrylates, carbonyl sulfide (COS), cyclic thioanhydrides, CO, and selenium powder. The polymerization is usually carried out under mild conditions: at 60 to 90 °C, for 2 to 12 h, using organobases as the catalysts or catalyst-free. This approach achieves the simultaneous incorporation of in-chain ester and sulfur/selenium functional groups including thiocarbonate, thioether, thioester, thiourethane, and selenoether.The method has a wide monomer scope and yields diverse polymers with tunable structures. The obtained polyesters possess weight-average molecular weights of up to 175.4 kDa. Most of these polyesters are thermally stable, exhibiting decomposition temperatures of >200 °C. Due to the diversity of structure, these polymers demonstrate extensively tunable performance covering crystalline plastics, thermoplastic elastomers, and amorphous plastics. These polymers exhibit a wide range of glass-transition temperatures of -60 to 72 °C and a wide range of melting temperatures of 43 to 274 °C. Notably, the polymers containing long alkyl chains (number of carbon atoms ≥ 9) exhibit polyethylene-like crystallinity and mechanical properties. The in-chain thiourethane or amide groups enable enhanced thermal and mechanical properties due to the incorporation of inter/intramolecular hydrogen bonding. These polymers are also easy to degrade via alkali hydrolysis, alcohol hydrolysis, enzymatic hydrolysis, oxidation, etc. The degradation products often have well-defined structure and value-added properties and can even be directly used for repolymerization to achieve a closed-loop chemical cycle. Overall, the multicomponent polymerization presented in this Account furnishes a facile and versatile synthesis of sustainable polymers with tunable structure and properties.

High-performance chemically recyclable multifunctional polyolefin-like biomass-derived polyester materials

Polyolefins are the most widely used and produced petroleum-based plastics. Unfortunately, the enormous production and usage of traditional polyolefins, coupled with the lack of effective disposal or recycling options, have led to significant fossil fuel depletion and severe environmental pollution. To foster sustainable societal development, there is an urgent need to design high-performance and inherently recyclable polyolefin-like bio-derived materials by innovative structural and molecular designs. Here, inspired by a copolymerization molecular design approach that simultaneously confers recyclability and superior properties to materials, high-performance recyclable polyolefin-like bio-derived polyesters (PBCxS) enabled by a novel judicious combination of building blocks are reported. PBCxS display excellent mechanical (40.6 MPa, 498.4%) and gas barrier properties (O2 0.09 barrer, H2O 1.70 × 10-13 g cm cm-2 s-1 Pa-1), even greater than those of bio-based materials and most aliphatic polyester. Meanwhile, PBCxS also exhibit multifunctionality with excellent biocompatibility properties and ultra-high processability (thermoforming, extrusion spinning, and 3D printing processing). Notably, PBCxS undergo depolymerization in the absence of any additional organic solvents, regenerating 92.0% of the high-purity (98.3%) original monomers, even with polyolefin blend plastics. Repolymerized polyesters still maintain their exceptional mechanical and thermal qualities. The successful application of this approach in polyesters opens up exciting possibilities for designing high-performance and recyclable bio-derived polyolefin-like materials.

Sustainable Plastics with High Performance and Convenient Processibility

Designing and making sustainable plastics is especially urgent to reduce their ecological and environmental impacts. However, it remains challenging to construct plastics with simultaneous high sustainability and outstanding comprehensive performance. Here, a composite strategy of in situ polymerizing a petroleum-based monomer with the presence of an industrialized bio-derived polymer in a quasi-solvent-free system is introduced, affording the plastic with excellent mechanical robustness, impressive thermal and solvent stability, as well as low energy, consumes during production, processing, and recycling. Particularly, the plastic can be easily processed into diverse shapes through 3D printing, injection molding, etc. during polymerization and further reprocessed into other complex structures via eco-friendly hydrosetting. In addition, the plastic is mechanically robust with Young's modulus of up to 3.7 GPa and tensile breaking strength of up to 150.2 MPa, superior to many commercially available plastics and other sustainable plastics. It is revealed that hierarchical hydrogen bonds in plastic predominate the well-balanced sustainability and performance. This work provides a new path for fabricating high-performance sustainable plastic toward practical applications, contributing to the circular economy.

Lifecycle Management for Sustainable Plastics: Recent Progress from Synthesis, Processing to Upcycling

Plastics, renowned for their outstanding properties and extensive applications, assume an indispensable and irreplaceable role in modern society. However, the ubiquitous consumption of plastic items has led to a growing accumulation of plastic waste. Unreasonable practices in the production, utilization, and recycling of plastics have led to substantial energy resource depletion and environmental pollution. Herein, the state-of-the-art advancements in the lifecycle management of plastics are timely reviewed. Unlike typical reviews focused on plastic recycling, this work presents an in-depth analysis of the entire lifecycle of plastics, covering the whole process from synthesis, processing, to ultimate disposal. The primary emphasis lies on selecting judicious strategies and methodologies at each lifecycle stage to mitigate the adverse environmental impact of waste plastics. Specifically, the article delineates the rationale, methods, and advancements realized in various lifecycle stages through both physical and chemical recycling pathways. The focal point is the attainment of optimal recycling rates for waste plastics, thereby alleviating the ecological burden of plastic pollution. By scrutinizing the entire lifecycle of plastics, the article aims to furnish comprehensive solutions for reducing plastic pollution and fostering sustainability across all facets of plastic production, utilization, and disposal.

Easy Synthetic Access to High-Melting Sulfurated Copolymers and their Self-Assembling Diblock Copolymers from Phenylisothiocyanate and Oxetane

Although sulfurated polymers promise unique properties, their controlled synthesis, particularly when it comes to complex and functional architectures, remains challenging. Here, we show that the copolymerization of oxetane and phenyl isothiocyanate selectively yields polythioimidocarbonates as a new class of sulfur containing polymers, with narrow molecular weight distributions (Mn=5-80 kg/mol with Đ≤1.2; Mn,max=124 kg/mol) and high melting points of up to 181 °C. The method tolerates different substituent patterns on both the oxetane and the isothiocyanate. Self-nucleation experiments reveal that π-stacking of phenyl substituents, the presence of unsubstituted polymer backbones, and the kinetically controlled linkage selectivity are key factors in maximising melting points. The increased tolerance to macro-chain transfer agents and the controlled propagation allows the synthesis of double crystalline and amphiphilic diblock copolymers, which can be assembled into micellar- and worm-like structures with amorphous cores in water. In contrast, crystallization driven self-assembly in ethanol gives cylindrical micelles or platelets.

Improved access to polythioesters by heterobimetallic aluminium catalysis

Bimetallic Al(III) catalysis mediates thioanhydride/epoxide copolymerisation at greatly improved rates and monomer tolerance than analogous Cr(III) catalysis. Moving to sulfurated monomers furthermore generally improves rates and selectivites.

Ring-Opening Terpolymerisation of Elemental Sulfur Waste with Propylene Oxide and Carbon Disulfide via Lithium Catalysis

Elemental sulfur, a waste product of the oil refinement process, represents a promising raw material for the synthesis of degradable polymers. We show that simple lithium alkoxides facilitate the polymerisation of elemental sulfur S8 with industrially relevant propylene oxide (PO) and CS2 (a base chemical sourced from waste S8 itself) to give poly(monothiocarbonate-alt-Sx) in which x can be controlled by the amount of supplied sulfur. The in situ generation of thiolate intermediates obtained by a rearrangement, which follows CS2 and PO incorporation, allows to combine S8 and epoxides into one polymer sequence that would otherwise not be possible. Mechanistic investigations reveal that alkyl oligosulfide intermediates from S8 ring opening and sulfur chain length equilibration represent the better nucleophiles for inserting the next PO if compared to the trithiocarbonates obtained from the competing CS2 addition, which causes the sequence selectivity. The polymers can be crosslinked in situ with multifunctional thiols to yield reprocessable and degradable networks. Our report demonstrates how mechanistic understanding allows to combine intrinsically incompatible building blocks for sulfur waste utilisation.

Synthesis and Deconstruction of Polyethylene-type Materials

Polyethylene deconstruction to reusable smaller molecules is hindered by the chemical inertness of its hydrocarbon chains. Pyrolysis and related approaches commonly require high temperatures, are energy-intensive, and yield mixtures of multiple classes of compounds. Selective cleavage reactions under mild conditions ( Collapse

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Grants

• H2020 European Research Council

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Affiliation(s)

Simon T. Schwab Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Maximilian Baur Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Taylor F. Nelson Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Stefan Mecking Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany

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EtOS2K as a C1 Source: Solvent- and Temperature-Controlled Selective Synthesis of Quinoline-2-thione and Quinoline-2-one Derivatives

Herein, we disclosed a highly chemoselective synthesis of quinoline-2-one and quinoline-2-thione derivatives using EtOS2K as the C1 source. Quinoline-2-one derivatives were synthesized selectively with NaCl as a catalyst in the solvent DMSO/H2O, while quinoline-2-thione derivatives were produced without the need for any catalyst in an environmentally friendly solvent EtOH/H2O. The reaction conditions were mild and had good functional group tolerance.

Copolymerization Involving Sulfur-Containing Monomers

Incorporating sulfur (S) atoms into polymer main chains endows these materials with many attractive features, including a high refractive index, mechanical properties, electrochemical properties, and adhesive ability to heavy metal ions. The copolymerization involving S-containing monomers constitutes a facile method for effectively constructing S-containing polymers with diverse structures, readily tunable sequences, and topological structures. In this review, we describe the recent advances in the synthesis of S-containing polymers via copolymerization or multicomponent polymerization techniques concerning a variety of S-containing monomers, such as dithiols, carbon disulfide, carbonyl sulfide, cyclic thioanhydrides, episulfides and elemental sulfur (S8). Particularly, significant focus is paid to precise control of the main-chain sequence, stereochemistry, and topological structure for achieving high-value applications.