Highly Efficient Biobased Synthesis of Acrylic Acid

Isosorbide-Based Acrylic Pressure-Sensitive Adhesives Through UV-Cured Crosslinking with a Balance Between Adhesion and Cohesion

The development of sustainable pressure-sensitive adhesives (PSAs) from natural biomass resources has attracted increasing attention owing to their non-toxic, biocompatible, and biodegradable features. In this study, a bio-based acrylic PSA with tunable adhesion and cohesion was synthesized by a selective chemical modification of isosorbide-5-acrylate (IA) and its copolymerization with butyl acrylate and acrylic acid through UV-curing crosslinking. During the UV-curing process, the synthesized isosorbide diacrylate ester (IDAE) served as the crosslinker, effectively improving the crosslinking degree of PSA. The impact of IA and IDAE on the mechanical properties of PSA was studied. Moreover, to achieve a balance between adhesion and cohesion, the optimal composition was identified. The addition of IA significantly enhances the stiffness of PSA. Furthermore, the combined effect of IA and IDAE improves the overall adhesion properties of the PSA. The optimal bio-based PSA demonstrates a peel force of 13.9 N/25 mm and a persistent time of 6820 min, promising to replace traditional petroleum-based PSAs.

Process Intensification of the Continuous Synthesis of Bio-Derived Monomers for Sustainable Coatings Using a Taylor Vortex Flow Reactor

We describe the optimization and scale-up of two consecutive reaction steps in the synthesis of bio-derived alkoxybutenolide monomers that have been reported as potential replacements for acrylate-based coatings (Sci. Adv.2020, 6, eabe0026). These monomers are synthesized by (i) oxidation of furfural with photogenerated singlet oxygen followed by (ii) thermal condensation of the desired 5-hydroxyfuranone intermediate product with an alcohol, a step which until now has involved a lengthy batch reaction. The two steps have been successfully telescoped into a single kilogram-scale process without any need to isolate the 5-hydroxyfuranone between the steps. Our process development involved FTIR reaction monitoring, FTIR data analysis via 2D visualization, and two different photoreactors: (i) a semicontinuous photoreactor based on a modified rotary evaporator, where FTIR and 2D correlation spectroscopy (2D-COS) revealed the loss of the methyl formate coproduct, and (ii) our fully continuous Taylor Vortex photoreactor, which enhanced the mass transfer and permitted the use of near-stoichiometric equivalents of O2. The use of in-line FTIR monitoring and modeling greatly accelerated process optimization in the Vortex reactor. This led to scale-up of the photo-oxidation in 85% yield with a projected productivity of 1.3 kg day-1 and a space-time yield of 0.06 mol day-1 mL-1. Higher productivities could be achieved while sacrificing yield (e.g., 4 kg day-1 at 40% yield). The use of superheated methanol at 200 °C in a pressurized thermal flow reactor accelerated the second step, the thermal condensation of 5-hydroxyfuranone, from a 20 h batch reflux reaction (0.5 L, 85 g) to a space time of <1 min in a reactor only 3 mL in volume operating with projected productivities of >700 g day-1. Proof of concept for telescoping the two steps was established with an overall two-step yield of 67%, producing a process with a projected productivity of 1.1 kg day-1 for the methoxybutenolide monomer without any purification of the 5-hydroxyfuranone intermediate.

Natural polyphenolic antibacterial bio-adhesives for infected wound healing

Bio-adhesives used clinically, commonly have the ability to fill surgical voids and support wound healing, but which are devoid of antibacterial activity, and thus, could not meet the particular needs of the infected wound site. Herein, a series of natural polyphenolic antibacterial bio-adhesives were prepared via simple mixing and heating of polyphenols and acid anhydrides without any solvent or catalyst. Upon the acid anhydride ring opening and acylation reactions, various natural polyphenolic bio-adhesives could adhere to various substrates (i.e., tissue, wood, glass, rubber, paper, plastic, and metal) based on multi-interactions. Moreover, these bio-adhesives showed excellent antibacterial and anti-infection activity, rapid hemostatic performance and appropriate biodegradability, which could be widely used in promoting bacterial infection wound healing and hot burn infection wound repair. This work could provide a new strategy for strong adhesives using naturally occurring molecules, and provide a method for the preparation of novel multifunctional wound dressings for infected wound healing.

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.

Developing hydrogels for gene therapy and tissue engineering

Hydrogels are a class of highly absorbent and easily modified polymer materials suitable for use as slow-release carriers for drugs. Gene therapy is highly specific and can overcome the limitations of traditional tissue engineering techniques and has significant advantages in tissue repair. However, therapeutic genes are often affected by cellular barriers and enzyme sensitivity, and carrier loading of therapeutic genes is essential. Therapeutic gene hydrogels can well overcome these difficulties. Moreover, gene-therapeutic hydrogels have made considerable progress. This review summarizes the recent research on carrier gene hydrogels for the treatment of tissue damage through a summary of the most current research frontiers. We initially introduce the classification of hydrogels and their cross-linking methods, followed by a detailed overview of the types and modifications of therapeutic genes, a detailed discussion on the loading of therapeutic genes in hydrogels and their characterization features, a summary of the design of hydrogels for therapeutic gene release, and an overview of their applications in tissue engineering. Finally, we provide comments and look forward to the shortcomings and future directions of hydrogels for gene therapy. We hope that this article will provide researchers in related fields with more comprehensive and systematic strategies for tissue engineering repair and further promote the development of the field of hydrogels for gene therapy.

A Novel Polyfunctional Polyurethane Acrylate Derived from Castor Oil-Based Polyols for Waterborne UV-Curable Coating Application

Because of its unique molecular structure and renewable properties, vegetable oil has gradually become the focus of researchers. In this work, castor oil was first transformed into a castor oil-based triacrylate structure (MACOG) using two steps of chemical modification, then it was prepared into castor oil-based waterborne polyurethane acrylate emulsion, and finally, a series of coating materials were prepared under UV curing. The results showed that with the increase in MACOG content, the glass transition temperature of the sample was increased from 20.3 °C to 46.6 °C, and the water contact angle of its surface was increased from 73.85 °C to 90.57 °C. In addition, the thermal decomposition temperature, mechanical strength, and water resistance of the samples were also greatly improved. This study not only provides a new idea for the preparation of waterborne polyurethane coatings with excellent comprehensive properties but also expands the application of biomass material castor oil in the field of coating.

Heterogeneous Brønsted Catalysis in the Solvent-Free and Multigram-Scale Synthesis of Polyalcohol Acrylates: The Case Study of Trimethylolpropane Triacrylate

This article presents a thorough investigation into the synthesis of trimethylolpropane triacrylate (TMPTA) via the esterification reaction of trimethylolpropane (TMP) with acrylic acid using Amberlite™ 120 IR (H+), Amberlyst® 15, and Dowex™ 50WX8 resins as heterogeneous catalysts. Preliminary comparative tests explored the impact of air flow on water removal during the reaction and different acid-to-alcohol molar ratios (3:1, 6:1, or 9:1 mol:mol). The findings revealed that introducing air significantly enhances TMPTA yield and -OH group conversion, particularly at a 6:1 acid-to-alcohol molar ratio. Based on cost considerations, Amberlite™ 120 IR (H+) was selected as the preferred catalyst for further optimization. This included evaluating the effect of catalyst loading (10%, 5.0%, and 2.5% w/wtot) and assessing the impact of a pre-drying process on resin efficiency. The study concluded that optimal conditions did not necessitate drying, requiring 120 °C, a catalyst loading of 10% w/wtot, a 4 h reaction time, an acid:alcohol ratio of 6:1 mol:mol, the presence of MEHQ (0.1% mol/molAA), and air bubbling at 6 ± 1 Nl/h. Catalyst recycling was effectively implemented with a slight reduction in catalytic activity over consecutive runs. Furthermore, the study explored a scaled-up system with a mechanical stirrer, demonstrating the potential for multi-hundred grams scale-up. Considerations for optimizing the air flow stripping system are also highlighted. In summary, this study provides valuable insights into designing and optimizing the esterification process for TMPTA synthesis, laying the foundation for potential industrial applications.

Cellulose modification for sustainable polymers: overcoming problems of solubility and processing

Two new water-soluble cellulose derivatives were prepared by a two-step transformation with 1,3-propane sultone, followed by either maleic or succinic anhydride, thereby converting cellulose into a more easily processable form. It was found that the solubility was dependent on both the degree of substitution and the chemical properties of the substituents. The water-soluble cellulose has a molecular weight greater than 100 000 g mol-1 and both the morphology and molecular weight can be tuned by varying the reaction conditions. Furthermore, the flexible, two-step nature of the process allows for expansion of this methodology in order to prepare cellulose analogues for different applications.

Iron oxide-promoted photochemical oxygen reduction to hydrogen peroxide (H2O2)

Hydrogen peroxide (H2O2) is a valuable green oxidant with a wide range of applications. Furthermore, it is recognized as a possible future energy carrier achieving safe operation, storage and transportation. The photochemical production of H2O2 serves as a promising alternative to the waste- and energy-intensive anthraquinone process. Following the 12 principles of Green Chemistry, we demonstrate a facile and general approach to sustainable catalyst development utilizing earth-abundant iron and biobased sources only. We developed several iron oxide (FeOx) nanoparticles (NPs) for successful photochemical oxygen reduction to H2O2 under visible light illumination (445 nm). Achieving a selectivity for H2O2 of >99%, the catalyst material could be recycled for up to four consecutive rounds. An apparent quantum yield (AQY) of 0.11% was achieved for the photochemical oxygen reduction to H2O2 with visible light (445 nm) at ambient temperatures and pressures (9.4-14.8 mmol g-1 L-1). Reaching productivities of H2O2 of at least 1.7 ± 0.3 mmol g-1 L-1 h-1, production of H2O2 was further possible via sunlight irradiation and in seawater. Finally, a detailed mechanism has been proposed on the basis of experimental investigation of the catalyst's properties and computational results.

Visible-Light-Driven Furfural Oxidation over CuOx /Nb2 O5

Maleic anhydride (MA) is an important polyester monomer that can be produced from oxidizing renewable furfural derived from biomass. However, MA generation from furfural requires harsh reaction conditions, and suffers from low efficiency and solvent corrosion. Herein, we design a Nb2 O5 photocatalyst loaded of highly dispersed CuOx (CuOx /Nb2 O5 ), which selectively catalyzes furfural oxidation to MA and the precursor (5-hydroxy-2(5H)-furanone, HF). Due to CuOx loading and forming a complex of ligand to metal charge transfer (LMCT) between the Nb2 O5 surface and adsorbed furfural, the CuOx /Nb2 O5 absorbs visible light to activate furfural though Nb2 O5 has a large band-gap energy (3.2 eV). Singlet oxygen (1 O2 ) is the key active species for C-C bond cleavage and CO generation. MA and HF is produced with a combined yield of 59 % under optimized conditions. This work provides a mild way to provide renewable maleic anhydride via oxidative C-C bond cleavage.

Electron-Poor Butenolides: The Missing Link between Acrylates and Maleic Anhydride in Radical Polymerization

Butenolides are a class of 5-membered lactones that hold great potential as bio-based monomers to replace oil-derived acrylates, of which they are cyclic analogues. Despite this structural resemblance, the reactivity of the unsaturated ester moiety of electron-poor butenolides leans toward that of maleic anhydride, another essential monomer that does not homopolymerize but copolymerizes in a highly alternating fashion with polarized electron-rich comonomers. By studying the reactivity of 5-methoxy and 5-acyloxy butenolides through a combination of kinetics and density functional theory (DFT) experiments, we explain why electron-poor butenolides constitute a missing link between acrylates and maleic anhydride in radical polymerization.

The sustainable production of succinic anhydride from renewable biomass

The selective production of C4 bulk chemicals from biomass is significant to replace the traditional method from petroleum resource. In this work, the succinic anhydride (SAN) is directly prepared from bio-based furanic platform compounds utilizing the visible light-induced oxygenation process, in which m-tetraphenyl porphyrin (H₂TPP) and molecular oxygen was employed as the photocatalyst and terminal oxidant, respectively. Under optimal conditions, a 99.9% conversion with 97.8% selectivity of SAN was obtained from furoic acid (FAC) at room temperature. Moreover, the transformation of furfural and furfuryl alcohol with this system can also generate SAN, and the product selectivity is controllable by tuning light intensity and time. Furthermore, the EPR detection, isotope labeling, and control experiments exhibited that the generation of singlet oxygen plays a crucial role and 5-hydroxy-2(5H)-furanone is the main intermediate during the reaction. Finally, a possible reaction mechanism for the production of SAN from furanic compound is proposed.

Hydrazone-based boron difluoride complexes as triplet photosensitizers for singlet oxygen generation

Due to the highly selective nature of singlet oxygen as an oxidant, it has received considerable interest in various areas of (organic) chemistry. Two green light activated hydrazone-based boron difluoride triplet photosensitizers possessing high quantum yields for ¹O₂ formation are reported. These photostable complexes are promising in applications in synthesis and catalysis.

The Diverse Modes of Oxygen Reactivity in Life & Chemistry

Oxygen is a molecule of utmost importance in our lives. Beside its vital role for the respiration and sustaining of organisms, oxygen is involved in numerous chemical and physical processes. Upon combination of the different forms of molecular oxygen species with various activation modes, substrates, and reaction conditions an extremely wide chemical space can be covered that enables rich applications of diverse oxygenation processes. This Review provides an instructive overview of the individual properties and reactivities of oxygen species and illustrates their importance in nature, everyday life, and in the context of chemical synthesis.

Development of a modular photoreactor for the upscaling of continuous flow photochemistry

The upscaling of biphasic photochemical reactions is challenging because of the inherent constraints of liquid-gas mixing and light penetration. Using semi-permeable coaxial flow chemistry within a modular photoreactor, the photooxidation of the platform chemical furfural was scaled up to produce routinely 29 gram per day of biobased building block hydroxybutenolide, a precursor to acrylate alternatives.

A Chemically Recyclable Crosslinked Polymer Network Enabled by Orthogonal Dynamic Covalent Chemistry

Chemical recycling of synthetic polymers offers a solution for developing sustainable plastics and materials. Here we show that two types of dynamic covalent chemistry can be orthogonalized in a solvent-free polymer network and thus enable a chemically recyclable crosslinked material. Using a simple acylhydrazine-based 1,2-dithiolane as the starting material, the disulfide-mediated reversible polymerization and acylhydrazone-based dynamic covalent crosslinking can be combined in a one-pot solvent-free reaction, resulting in mechanically robust, tough, and processable crosslinked materials. The dynamic covalent bonds in both backbones and crosslinkers endow the network with depolymerization capability under mild conditions and, importantly, virgin-quality monomers can be recovered and separated. This proof-of-concept study show opportunities to design chemically recyclable materials based on the dynamic chemistry toolbox.

Photocatalyzed Functionalization of Alkenoic Acids in 3D-Printed Reactors

The valorization of alkenoic acids possibly deriving from biomass (fumaric and citraconic acids) was carried out through conversion in important building blocks, such as γ-keto acids and succinic acid derivatives. The functionalization was carried out by addition onto the C=C double bond of radicals generated under photocatalyzed conditions from suitable hydrogen donors (mainly aldehydes) and by adopting a decatungstate salt as the photocatalyst. Syntheses were performed under batch (in a glass vessel) and flow (by using 3D-printed reactors) conditions. The design of the latter reactors allowed for an improved yield and productivity.

Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications

Long triplet lifetimes of excited photosensitizers are essential for efficient energy transfer reactions in water, given that the concentrations of dissolved oxygen and suitable acceptors in aqueous media are typically much lower than in organic solvents. Herein, we report the design, synthesis and photochemical characterization of two structurally related water-soluble ruthenium complex-based dyads decorated with a covalently attached pyrene chromophore. The triplet energy of the latter is slightly below that of the metal complex enabling a so-called triplet reservoir and excited-state lifetime extensions of up to two orders of magnitude. The diimine co-ligands, which can be modified easily, have a major impact on both the ultrafast intramolecular energy transfer (iEnT) kinetics upon excitation with visible light and the lifetime of the resulting long-lived pyrene triplet. The phenanthroline-containing dyad shows fast triplet pyrene formation (25 ps) and an exceptionally long triplet lifetime beyond 50 microseconds in neat water. The iEnT process via the Dexter mechanism is slower by a factor of two when bipyridine co-ligands are employed, which is rationalized by a poor orbital overlap. Both dyads are very efficient sensitizers for the formation of singlet oxygen in air-saturated water as well as for the bimolecular generation of anthracene triplets that are key intermediates in upconversion mechanisms. This is demonstrated by the 5-hydroxymethylfurfural oxidation, which yields completely different main products depending on the pH value of the aqueous solution, as an initial application-related experiment and by time-resolved spectroscopy. Our findings are important in the greater contexts of photocatalysis and energy conversion in the "green" solvent water.