Randomly Distributed Sulfur Atoms in the Main Chains of CO2 -Based Polycarbonates: Enhanced Optical Properties

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.

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.

Sustainable Polymers with High Performance and Infinite Scalability

Our society has been pursuing high-performance biodegradable polymers made from facile methods and readily available monomers. Here, we demonstrate a library of enzyme-degradable polymers with desirable properties from the first reported step polyaddition of diamines, COS, and diacrylates. The polymers contain in-chain ester and thiourethane groups, which can serve as lipase-degradation and hydrogen-bonding physical crosslinking points, respectively, resulting in possible biodegradability as well as upgraded mechanical and thermal properties. Also, the properties of the polymers are scalable due to the versatile method and the wide variety of monomers. We obtain 46 polymers with tunable performance covering high-Tm crystalline plastics, thermoplastic elastomers, and amorphous plastics by regulating polymer structure. Additionally, the polymerization method is highly efficient, atom-economical, quantitatively yield, metal- and even catalyst-free. Overall, the polymers are promising green materials given their degradability, simple and modular synthesis, remarkable and tunable properties, and readily available monomers.

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.

Precise cooperative sulfur placement leads to semi-crystallinity and selective depolymerisability in CS2/oxetane copolymers

CS₂ promises easy access to degradable sulfur-rich polymers and insights into how main-group derivatisation affects polymer formation and properties, though its ring-opening copolymerisation is plagued by low linkage selectivity and small-molecule by-products. We demonstrate that a cooperative Cr(III)/K catalyst selectively delivers poly(dithiocarbonates) from CS₂ and oxetanes while state-of-the-art strategies produce linkage scrambled polymers and heterocyclic by-products. The formal introduction of sulfur centres into the parent polycarbonates results in a net shift of the polymerisation equilibrium towards, and therefore facilitating, depolymerisation. During copolymerisation however, the catalyst enables near quantitative generation of the metastable polymers in high sequence selectivity by limiting the lifetime of alkoxide intermediates. Furthermore, linkage selectivity is key to obtain semi-crystalline materials that can be moulded into self-standing objects as well as to enable chemoselective depolymerisation into cyclic dithiocarbonates which can themselves serve as monomers in ring-opening polymerisation. Our report demonstrates the potential of cooperative catalysis to produce previously inaccessible main-group rich materials with beneficial chemical and physical properties.

Advancing the Development of Recyclable Aromatic Polyesters by Functionalization and Stereocomplexation

The development of innovative synthetic polymer systems to overcome the trade-offs between the polymer's depolymerizability and performance properties is in high demand for advanced material applications and sustainable development. In this contribution, we prepared a class of aromatic cyclic esters (M1-M5) from thiosalicylic acid and epoxides by facile one-pot synthesis. Ring-opening polymerization of Ms afforded aromatic polyesters P(M)s with high molecular weights and narrow dispersities. The physical and mechanical properties of P(M)s can be modulated by stereocomplexation and regulation of the side-chain flexibility of the polymers, ultimately achieving high-performance properties such as high thermal stability and crystallinity (T_m up to 209 °C), as well as polyolefin-like high mechanical strength, ductility, and toughness. Furthermore, the functionalizable moieties of P(M)s have driven a wide array of post-polymerization modifications toward access to value-added materials. More importantly, the P(M)s were able to selectively depolymerize into monomers in excellent yields, thus establishing its circular life cycle.

Copolymerization of SO2 with propylene oxide mediated by organic ammonium salts: A comprehensive study of main-chain structure, living polymerization character and regioselectivity

The utilization of sulfur dioxide (SO2) for constructing sulfur-containing polymers is of much significance in term with either environment issue or obtaining high-valued materials. The copolymerization of SO2 with epoxides...

Sulfur-containing polymers derived from SO2: synthesis, properties, and applications

Sulfur-containing polymers enjoy the merits of excellent optical performance, degradation, chemical recyclability, and adhesive abilities toward metal ions. Recently, increasing attentions in both academic and industrial circles have been paid...

Facile construction of functional poly(monothiocarbonate)s copolymers under mild operating conditions

The installation of both oxazolidone and thiocarbonate linkages within a single polymer backbone remains elusive by simple procedures under mild conditions. In this work, we report the construction of copolymers...

COS-triggered oxygen/sulfur exchange of isatins: chemoselective synthesis of functionalized isoindigos and spirothiopyrans via self-condensation and the thio-Diels-Alder reaction

Herein, we present the first organocatalytic oxygen/sulfur atom exchange reaction (O/S ER) of isatins by employing carbonyl sulfide (COS) as a novel sulfuring reagent under mild reaction conditions. 8-Diazabicyclo[5.4.0]undec-7-ene (DBU) exhibited excellent activity in this approach. Remarkably, the chemical transformations of in situ generated 3-thioisatins can be tuned via the judicious choice of reaction solvents in a one pot process, enabling the selective formation of either functionalized isoindigos in CH₃CN via a self-condensation process or spirothiopyrans in DMSO in the presence of conjugated dienes via the thio-Diels-Alder reaction. Mechanistic studies with experimental and density functional theory approaches revealed that the O/S ER between isatins and COS results in the formation of 3-thioisatins as the key intermediates, which further undergo solvent-controlled transformations to generate isoindigos or spirothiopyrans, respectively. The easily-accessible substrates and operational simplicity make the process suitable for further exploration. The practicality of this transformation was demonstrated by the gram-scale synthesis of isoindigo-based drug molecules and donor-acceptor conjugated polymers.

One-Pot Construction of Sulfur-Rich Thermoplastic Elastomers Enabled by Metal-Free Self-Switchable Catalysis and Air-Assisted Coupling

Construction of well-defined sulfur-rich macromolecules in a facile manner is an interesting but challenging topic. Herein, we disclose how to readily construct well-defined triblock sulfur-rich thermoplastic elastomers via a self-switchable isothiocyanate/episulfide copolymerization and air-assisted oxidative coupling strategy. During self-switchable polymerization, alternating copolymerization of isothiocyanate and episulfide occurs initially due to the lower energy barrier for isothiocyanate insertion with respect to successive episulfide ring-opening. After exhaustion of isothiocyanate, ring-opening polymerization of episulfide begins, providing diblock polymers. Subsequent exposure of the reaction to air leads to a transformation of diblock copolymers into triblock thermoplastic elastomers. This protocol can be extended to diverse isothiocyanates and episulfides, allowing fine-tuning of the performance of the produced sulfur-rich thermoplastic elastomers.

Sequence Control from Mixtures: Switchable Polymerization Catalysis and Future Materials Applications

There is an ever-increasing demand for higher-performing polymeric materials counterbalanced by the need for sustainability throughout the life cycle. Copolymers comprising ester, carbonate, or ether linkages could fulfill some of this demand as their monomer-polymer chemistry is closer to equilibrium, facilitating (bio)degradation and recycling; many monomers are or could be sourced from renewables or waste. Here, an efficient and broadly applicable route to make such copolymers is discussed, a form of switchable polymerization catalysis which exploits a single catalyst, switched between different catalytic cycles, to prepare block sequence selective copolymers from monomer mixtures. This perspective presents the principles of this catalysis, catalyst design criteria, the selectivity and structural copolymer characterization tools, and the properties of the resulting copolymers. Uses as thermoplastic elastomers, toughened plastics, adhesives, and self-assembled nanostructures, and for programmed degradation, among others, are discussed. The state-of-the-art research into both catalysis and products, as well as future challenges and directions, are presented.

Heterocycle/Heteroallene Ring-Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

Heteroatom‐containing polymers have strong potential as sustainable replacements for petrochemicals, show controllable monomer–polymer equilibria and properties spanning plastics, elastomers, fibres, resins, foams, coatings, adhesives, and self‐assembled nanostructures. Their current and future applications span packaging, house‐hold goods, clothing, automotive components, electronics, optical materials, sensors, and medical products. An interesting route to these polymers is the catalysed ring‐opening copolymerisation (ROCOP) of heterocycles and heteroallenes. It is a living polymerization, occurs with high atom economy, and creates precise, new polymer structures inaccessible by traditional methods. In the last decade there has been a renaissance in research and increasing examples of commercial products made using ROCOP. It is better known in the production of polycarbonates and polyesters, but is also a powerful route to make N‐, S‐, and other heteroatom‐containing polymers, including polyamides, polycarbamates, and polythioesters. This Review presents an overview of the different catalysts, monomer combinations, and polymer classes that can be accessed by heterocycle/heteroallene ROCOP.

The synthesis of degradable sulfur-containing polymers: precise control of structure and stereochemistry

This review comprehensively summarized the recent progresses made in the precise synthesis of sulfur-containing polymers from the structure control, stereochemistry control and the topological structure modification aspects.