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

Facile synthesis of recyclable polythioimidocarbonates via aromatization-driven alternating copolymerization of para-quinone methide and isothiocyanates

The efficient and controllable alternating copolymerization of para-Quinone Methide (p-QM) is rare and challenging. The aromatization-driven alternating copolymerization of p-QM with isothiocyanates is explored for the first time under mild conditions. In the presence of the key catalyst m-phthalic acid and the initiator TBD, the reaction can efficiently produce completely alternating polythioimidocarbonates with narrow molecular weight distributions and high molar mass (up to 103.6 kg mol-1). Experimental studies and DFT calculations suggest that m-phthalic acid plays a synergistic catalytic role. Remarkably, copolymers can be recycled back into monomers with excellent yields under vacuum at a temperature of 190 °C in just a few minutes without solvents or catalysts.

Biocatalytic enantioselective formation and ring-opening of oxetanes

Although biocatalysis offers complementary or alternative approaches to traditional synthetic methods, the limited range of available enzymatic reactions currently poses challenges in synthesizing a diverse array of desired compounds. Consequently, there is a significant demand for developing novel biocatalytic processes to enable reactions that were previously unattainable. Herein, we report the discovery and subsequent protein engineering of a unique halohydrin dehalogenase to develop a biocatalytic platform for enantioselective formation and ring-opening of oxetanes. This biocatalytic platform, exhibiting high efficiency, excellent enantioselectivity, and broad scopes, facilitates the preparative-scale synthesis of chiral oxetanes and a variety of chiral γ-substituted alcohols. Additionally, both the enantioselective oxetane formation and ring-opening processes are proven scalable for large-scale transformations at high substrate concentrations, and can be integrated efficiently in a one-pot, one-catalyst cascade system. This work expands the enzymatic toolbox for non-natural reactions and will promote further exploration of the catalytic repertoire of halohydrin dehalogenases in synthetic and pharmaceutical chemistry.

Monomer centred selectivity guidelines for sulfurated ring-opening copolymerisations

Sulfur-containing polymers, such as thioesters and thiocarbonates, offer sustainability advantages, including enhanced degradability and chemical recyclability. However, their synthesis remains underdeveloped compared to that of their oxygen-containing counterparts. Although catalytic ring-opening copolymerization (ROCOP) can provide access to sulfur-containing polymers, these materials often exhibit uncontrolled microstructures and unpredictable properties. A comprehensive model that elucidates the factors determining selectivity in these catalytic reactions is still lacking, despite its central importance for advancing these polymerizations into widely applicable methodologies. In this study, we investigate the factors that lead to selectivity in sulfurated ROCOP across various monomer combinations, including thioanhydrides or carbon disulfide with epoxides, thiiranes, and oxetanes. We find that unwanted by-products primarily arise from backbiting reactions of catalyst-bound alkoxide chain ends, which can be mitigated by (i) selecting monomers that form primary alkoxide of thiolate chain ends, (ii) maximizing ring strain in the backbiting step, and (iii) timely termination of the polymerization. By applying these strategies, the selectivity of the catalytic ROCOP can be controlled and we successfully synthesized perfectly alternating poly(esters-alt-thioesters) from various oxetanes and the highly industrially relevant ethylene oxide. Our study thereby shifts the focus for achieving selectivity from catalyst to monomer choice providing valuable mechanistic insights for the development of future selective polymerizations, paving the way for sulfurated polymers as potential alternatives to current commodity materials.

O/S Exchange Reaction in Synthesizing Sulfur-Containing Polymers

Using carbon disulfide (CS2) and carbonyl sulfide (COS) as sulfur-containing and one-carbon feedstocks to make value-added products is paramount for both pure and applied chemistry and environmental science. One of the practical strategies is to copolymerize these bulk chemicals with epoxides to produce sulfur-containing polymers. This approach contributes to improving the sustainability of polymer manufacturing, provides highly desired functional polymer materials, and has attracted much attention. However, these copolymerizations invariably exhibit the intensely complicated chemistry of O/S exchange reaction, leading to sulfur-containing polymers with diverse architectures. As the understanding of O/S exchange continues to deepen, recent efforts have guided significant advances in the synthesis of CS2- and COS-based polymers. This review examines the O/S exchange chemistry and summarizes the recent progress in this field to promote the further advance of synthesizing sulfur-containing polymers from CS2 and COS.

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.

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.

Decoupling of the Confused Complex in Oxidation of 3,3',5,5'-Tetramethylbenzidine for the Reliable Chromogenic Bioassay

Regulation of the reaction pathways is a perennial theme in the field of chemistry. As a typical chromogenic substrate, 3,3',5,5'-tetramethylbenzidine (TMB) generally undertakes one-electron oxidation, but the product (TMBox1) is essentially a confused complex and is unstable, which significantly hampers the clinic chromogenic bioassays for more than 50 years. Herein, we report that sodium dodecyl sulfate (SDS)-based micelles could drive the direct two-electron oxidation of TMB to the final stable TMBox2. Rather than activation of H2O2 oxidant in the one-electron TMB oxidation by common natural peroxidase, activation of the TMB substrate by SDS micelles decoupled the thermodynamically favorable complex between TMBox2 with unreacted TMB, leading to an unusual direct two-electron oxidation pathway. Mechanism studies demonstrated that the complementary spatial and electrostatic isolation effects, caused by the confined hydrophobic cavities and negatively charged outer surfaces of SDS micelles, were crucial. Further cascading with glucose oxidase, as a proof-of-concept application, allowed glucose to be more reliably measured, even in a broader range of concentrations without any conventional strong acid termination.

Precise construction of weather-sensitive poly(ester-alt-thioesters) from phthalic thioanhydride and oxetane

We report the selective ring opening copolymerisation (ROCOP) of oxetane and phthalic thioanhydride by a heterobimetallic Cr(III)K catalyst precisely yielding semi-crystalline alternating poly(ester-alt-thioesters) which show improved degradability due to the thioester links in the polymer backbone.