Search Results (90)

In the chemistry of bio-based furans, the Diels–Alder reaction plays an important role as a renewable route for the synthesis of fuels, fine chemicals, and monomers. Nonetheless, the unfavorable kinetic and thermodynamic parameters inherent to the Diels–Alder reaction involving furans as dienes often lead to the reversibility of cycloaddition, resulting in decreased equilibrium conversion and diastereoselectivity. In this study, we present a new strategy for overcoming the problem of reversibility in chemical reactions. We demonstrate that conducting the reaction under solvent-free conditions can facilitate the transition from a molten state formed by the initial reactants to a solid phase containing the reaction product along with an excess of the initial substrate. According to our results, such a liquid-to-solid transition of the reaction mixture can lead to exceptionally high conversion and diastereoselectivity in the furan–maleimide Diels–Alder reaction, particularly for challenging electron-poor furanic substrates. Our approach enables the reversible furan–maleimide Diels–Alder reaction to be performed in a cleaner and more environmentally friendly manner, free from the complexities associated with the use of solvents and the need for purification from side products. Full article

Chiral covalent organic frameworks (COFs) hold great promise in heterogeneous asymmetric catalysis due to their designable structures and well-defined chiral microenvironments. However, precise control over the pore size of chiral COFs to optimize asymmetric catalytic performance remains challenging. Herein, we designed a proline-derived dihydrazide chiral monomer (L-DBP-Boc), which was subjected to Schiff-base reactions with two aromatic aldehydes of different lengths, 1,3,5-triformyl phloroglucinol (BTA) and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (TZ), to construct two hydrazone-linked chiral COFs with distinct pore sizes (L-DBP-BTA COF and L-DBP-TZ COF). Interestingly, the Boc protecting groups were removed in situ during COF synthesis. We systematically investigated the catalytic performance of these two chiral COFs in asymmetric aldol reactions and found that their pore sizes significantly influenced both catalytic activity and enantioselectivity. The large-pore L-DBP-TZ COF (pore size: 3.5 nm) exhibited superior catalytic performance under aqueous conditions at room temperature, achieving a yield of 98% and an enantiomeric excess (ee) value of 78%. In contrast, the small-pore L-DBP-BTA COF (pore size: 2.0 nm) showed poor catalytic performance. Compared to L-DBP-BTA COF, L-DBP-TZ COF demonstrated a 1.69-fold increase in yield and a 1.56-fold enhancement in enantioselectivity, possibly attributed to the facilitated diffusion and transport of substrates and products within the larger pore, thus improving the accessibility of active sites. This study presents a facile synthesis of pyrrolidine-functionalized chiral COFs and establishes the possible structure–activity relationship in their asymmetric catalysis, offering new insights for the design of efficient chiral COF catalysts. Full article

In the field of water-based inks, the use of alkali-soluble resins (ASRs) as polymeric surfactants for synthesizing polyacrylate latexes has become a mainstream method. This study first designed and prepared crosslinkable ASRs with a diacetone acrylamide (DAAM) crosslinking monomer via emulsion polymerization. These ASRs were then employed as surfactants to synthesize self-crosslinking polyacrylate latexes through an in situ one-pot method, systematically investigating the influence of crosslinkable ASRs on the properties of the corresponding polyacrylate latexes. The research revealed that all prepared polyacrylate latexes exhibited a core–shell structure. With increasing DAAM content in the ASRs, the latex particle size gradually increased while the particle size distribution narrowed. All latexes demonstrated excellent stability, with absolute ζ-potential values exceeding 30 mV. The introduction of DAAM into ASRs significantly increased the glass transition temperature in the high-temperature region of the corresponding latex films, with the tensile strength reaching a maximum of 7.96 MPa. Moderate crosslinking in ASRs substantially improved the water resistance of latex films. Crosslinking degree tests indicated that latex films prepared through either single shell-layer crosslinking or single core-layer crosslinking showed relatively low crosslinking degrees, while only the dual core–shell crosslinking strategy could effectively enhance the film crosslinking degree. However, excessively crosslinked shell layers significantly hindered the crosslinking reaction of DAAM in the core layer, leading to reduced overall film crosslinking. Additionally, incorporating a certain number of DAAM crosslinking groups in ASRs was found to improve the adhesion of corresponding water-based inks on PE and BOPP substrates, with adhesion on BOPP substrates reaching up to 100%. Full article

In this study, we present a sponge-like lipophilic gel crosslinked with a branched crosslinker as an absorbent for VOC removal. The gel was synthesized by crosslinking the monomer 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) with the branched crosslinker poly(2-propyl aspartamide) grafted methacrylate (PPA-g-MA). The grafted crosslinker, PPA-g-MA, was prepared by introducing acrylate groups as crosslinking moieties to the poly(succinimide) precursor for poly(2-propyl aspartamide) (PPA), which serves as a hydrophobic backbone. Lipophilic gels were synthesized with varying TMSPMA monomer concentrations and freeze-dried to form a porous structure. To evaluate VOC absorption, the toluene removal efficiency of the sponge-like lipophilic gel was tested in a continuous gas flow system. As a result, the optimal TMSPMA monomer content for maximizing toluene removal efficiency was determined. This result suggests that while an increase in silicon content generally enhances VOC removal efficiency, the porous structure of sponge-like lipophilic gels plays a more crucial role in absorption capacity. The collapse of the porous structure, caused by excessive silicon content making the material more rubber-like, explains why there exists an optimal monomer content for effective VOC absorption. Overall, these findings provide valuable insights for developing high-performance VOC absorbents. Full article

Recent research on incorporating biomass resources into functional polymers has garnered significant attention. Poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) is the most commercially successful conducting polymer composed of over 70 wt% petroleum-derived PSS, which presents an opportunity for partial replacement with biomass-based resources. In this study, a complex of PEDOT and sulfated cellulose nanofiber (PEDOT:s-CNF) was synthesized, and the relationship between its conductivity and doping conditions was investigated. PEDOT was synthesized on s-CNF, which was used in place of PSS, and the results indicate that conductivity increases as PEDOT polymerization progresses; however, excessive polymerization reduces electrical conductivity. Based on X-ray photoelectron spectroscopy and zeta potential measurements, the doping concentration decreases as PEDOT polymerization progresses to an excess state. This decrease is attributed to the depletion of sulfate groups, which act as dopants on s-CNFs, occurring as a consequence of the addition of PEDOT monomers. Enhancing the degree of sulfate group substitution on s-CNFs and incorporating additional dopants containing sulfonic groups improved conductivity. Specifically, adding p-toluenesulfonic acid (PTSA) as a dopant increased conductivity, reaching approximately 10 mS cm⁻¹. However, at higher PTSA concentrations, the strong acidity of sulfonic groups reduced the degree of sulfate group dissociation, leading to a decline in doping efficiency. Full article

A rapid microwave-assisted process minimizing waste was set up to produce bio-based benzoxazine-like monomers produced from vanillylamine and melamine. Without excessive purification, different viscous liquid precursors had a remarkable ability to form four strong and transparent different solid cross-linked thermosets, displaying lower curing temperatures under 130 °C. The long and strong adhesive performance of the cured materials was observed using glass slides or aluminum surfaces and they could become a good alternative to adhesive epoxy resin for metal surfaces. At the higher temperatures, these solids could act as efficient flame-retardants proven by thermogravimetric measurements. The best candidates gave a limiting oxidation index value of 41.9. In order to improve the intrinsic surface hydrophobicity of the phenolic resins, slight amounts of silica and iron oxide nanoparticles were dispersed in the polymer matrix, and finally mechanical resistance was pointed out. The most promising of our melamine-based resin was loaded with aluminum pigment to furnish a silver-colored paste ready for being cured to afford a robust solid, which does not undergo contraction or deformation. Full article

The potassium alumanyl [{SiN^Dipp}AlK]₂ (SiN^Dipp = {CH₂SiMe₂NDipp}₂; Dipp = 2,6-i-Pr₂C₆H₃) reacts with organic azides via reductive N₂ elimination. With the less sterically encumbered azides PhN₃ and C₁₀H₁₅N₃ (1-azidoadamantane), the putative initially formed aluminium imide undergoes facile [2 + 3] cycloaddition to provide the tetrazenylaluminates [{SiN^Dipp}Al-κ²-N,N′-({N(R)}₂N₂)]K (R = Ph, C₁₀H₁₅). In contrast, each Al(I) centre of [{SiN^Dipp}AlK]₂ only reacts with a single equivalent of 2,4,6-Me₃C₆H₂N₃ to provide the imidoaluminate [{SiN^Dipp}AlN(2,4,6-Me₃C₆H₂)(K∙C₆H₆)], which crystallises as a monomer and displays a short Al-N distance of 1.7040(13) Å. Attempts to synthesise the azide [{SiN^Dipp}AlN₃] by reaction of [{SiN^Dipp}AlI] with an excess of KN₃ resulted in exclusive formation of the bis(azido)aluminate [{SiN^Dipp}Al(N₃)₂K], which crystallises as an infinite 1-dimensional polymer propagated by μ-(1,3)-N₃ bridging interactions between the potassium cations and azide anions. Although the THF-adducted azide [{SiN^Dipp}AlN₃(THF)] may be synthesised and characterised by more stringent control of the reaction stoichiometry, the synthetic viability of this route remains compromised by competitive generation of [{SiN^Dipp}Al(N₃)₂K]. Full article

The influence of the molecular weight and chemical structure of polyphenylene sulfone (PPSU) end groups on the formation of the porous structure of ultrafiltration (UF) hollow fiber membranes was investigated. Polymers with a molecular weight ranging from 67 to 81 kg/mol and with a hydroxyl-to-chlorine end group ratio ranging from 0.43 to 17.0 were synthesized. The excess of end groups was achieved during polymer synthesis by adding one of the following monomers: hydroxyl (excess DHBP) or chlorine (excess DCDPS). For the first time, it was found that the stability of PPSU solutions is determined not by the molecular weight of the polymer, but by the chemical structure of its end groups. The stability of polymer solutions increases with the increasing proportion of chlorine groups. The SEM method showed that with the increasing molar fraction of chlorine end groups in the polymer, a more open porous structure forms on the outer surface of the hollow fiber membranes derived from it. The maximum UF permeance of the hollow fiber membranes for water was achieved with the PPSU sample containing the highest chlorine end group content, amounting to 136 L/(m²·h·bar), with a high rejection of the model substance Blue Dextran (at 94.7%). This represents the best result currently reported among unmodified PPSU hollow fiber membranes. Full article

A polymer is a long-chain molecule formed by linking numerous simpler repeating chemical units, known as monomers, with identical structures. Over the past two centuries, there has been a significant increase in the global production and use of petrochemical-based plastics. This surge has led to widespread ecological imbalances, affecting air quality, terrestrial and marine ecosystems, food chains, and plant life. Consequently, the excessive use of such polymers has created challenges in solid waste management, with methods like bio- or photo-degradation, incineration, landfilling, and recycling proving to be time-consuming and laborious. Therefore, there is a growing urgency for biodegradable polymers due to increasing demand. Biodegradable polymers consist of interconnected monomers with unstable links in the backbone, facilitated by various functional groups. Throughout the degradation process of these polymers, numerous biologically acceptable molecules are produced. This study examines the significance of biopolymers over petroleum-based counterparts, offering a detailed analysis. It is noteworthy that within the spectrum of biodegradable polymers, polyhydroxyalkanoates (PHAs) emerge as exceptionally promising candidates for substituting petroleum-derived polymers, owing to their remarkable physical attributes. Therefore, this study provides a systematic overview of PHAs, including their classification, historical background, methods of production, potential challenges to commercialization, and diverse applications. Full article

The polymerization mechanism of para-methoxystyrene catalyzed by cationic α-diimine palladium complexes with various ancillary ligands was rigorously examined using density functional theory. In the classical methyl-based α-diimine palladium complex [{(2,6-ⁱPr₂C₆H₃)-N=C(Me)-C(Me)=N-2,6-ⁱPr₂C₆H₃)}PdMe]⁺ (A⁺), the 2,1-insertion of para-methoxystyrene is favored over the 1,2-insertion, both thermodynamically and kinetically, during the chain initiation step. The resulting thermodynamically favored η³-π-benzyl intermediates face a substantial energy barrier, yielding only trace amounts of polymer, as experimentally verified. In contrast, the dibenzobarrelene-based α-diimine palladium complex [{(2,6-ⁱPr₂C₆H₃)-N=C(R)-C(R)=N-2,6-ⁱPr₂C₆H₃)}PdMe]⁺ (R = dibenzobarrelene, B⁺) shows similar energy barriers for both 2,1- and 1,2-insertions. Continuous 2,1/2,1 or 2,1/1,2 insertions are impeded by excessive energy barriers. However, theoretical calculations reveal that the 1,2-insertion product can seamlessly transition into the chain propagation stage, producing a polymer with high 1,2-regioselectivity. The observed activity of complexes A⁺ or B⁺ towards para-methoxystyrene polymerization stems from the energy barrier differences between the 1,2- and 2,1-insertions, influenced by the steric hindrance from the ancillary ligands. Further investigation into the effects of steric hindrance on the chain initiation stage involved computational modeling of analogous complexes with increased steric bulk. These studies established a direct correlation between the energy barrier difference ∆∆G (1,2–2,1) and the van der Waals volume of the ancillary ligand. Larger van der Waals volumes correspond to reduced energy barrier differences, thus enhancing the regioselectivity for para-methoxystyrene polymerization. Moreover, the experimental inertness of complex B⁺ towards styrene polymerization is attributed to the formation of stable kinetic and thermodynamic 2,1-insertion intermediates, which obstruct further styrene monomer insertion due to an extremely high reactive energy barrier. These findings contribute to a deeper understanding of the mechanistic aspects and offer insights for designing new transition metal catalysts for the polymerization of para-alkoxystyrenes. Full article

Three novel bio-based monomers were synthesized through an amidation reaction involving allylated derivatives of coumaric, ferulic and phloretic acid and a diamine obtained from a thiol-ene coupling reaction between limonene and cysteamine. The monomers containing the enone bond of the cinnamic moiety underwent photoisomerization and photocycloaddition reactions upon UV light irradiation. All three monomers were photocured via thiol-ene photopolymerization using a glycerol-derived trifunctional thiol, resulting in fully bio-based poly(amide–thioether)s. The polymers derived from monomers that contain the enone bond exhibited glass transition (T_g) temperatures of 85 °C when a stoichiometric ratio of the thiol was used, whereas polymers in which an excess of thiol was used exhibited T_g temperatures of 61 and 74 °C. The higher T_g of the synthesized polymers, compared with other reported polymers produced from thiol-ene photopolymerizations, was attributed to the combination of the aromatic rings of the cinnamic moiety and the cycloaliphatic ring of limonene, as well as the presence of the amide groups in the polymer, which can induce hydrogen bonding. The development of high T_g polymers from bio-based monomers through thiol-ene photopolymerization represents a significant advancement in the polymer synthesis sector, offering an improved performance and sustainability. Full article

Aiming at the problem of excessive swelling of conventional microspheres for oilfield use, a novel amphiphilic polymerizable crosslinker (AE) was synthesized by quaternary ammonium modification of an unstable crosslinker (AE) using acrylamide, 2-acrylamido-2-methylpropanesulfonic acid as the monomers, N,N′-methylene bisacrylamide as the stabilizing crosslinker, ammonium peroxysulfate and sodium bisulfite as the initiator, and water as the solvent by using a reversed microemulsion method. Double-networked nanomicrospheres were prepared. The preparation conditions of the microspheres were optimized by the surface response method, focusing on the effects of the initiator addition and reaction temperature, and total crosslinker addition on the formation of nanomicrospheres. The samples were characterized by FTIR, TGA, laser particle sizer, and SEM to evaluate the retarded expansion performance and the modulation drive performance. The results showed that the optimal conditions for the preparation of microspheres were m(oil phase):m(water phase) = 3:2, stirring speed of 550 r/min, total crosslinking agent dosage of 0.6% (based on the total mass of monomers, hereinafter the same), initiator dosage of 0.30%, reaction temperature of 45 °C, and reaction time of 4 h. Compared with the conventional polymer microsphere PAM, PAE was slow-expanded for 45 d at 60 °C, and the expansion multiplier was about 16 times, with slow-expansion characteristics; the blocking rate of PAE reached 98.3%, the oil repulsion rate was 73.11%, and the increase in the recovery rate could be up to 11.23%. In this paper, a new type of nanomicrosphere material is investigated to realize the efficient implementation of oil field conditioning and driving. Full article

This article presents a method for producing chiral ionic liquid-based polyurea microcapsules that can be magnetically separated. The method involves entrapping hydrophilic magnetic nanoparticles within chiral polyurea microspheres. The synthetic process for creating these magnetic polyurea particles involves oil-in-oil (o/o) nano-emulsification of an ionic liquid-modified magnetite nanoparticle (MNPs-IL) and an ionic liquid-based diamine monomer, which comprises a chiral bis(mandelato)borate anion, in a nonpolar organic solvent, toluene, and contains a suitable surfactant. This is followed by an interfacial polycondensation reaction between the isocyanate monomer, polymethylenepolyphenyl isocyanate (PAPI 27), and the chiral diamine monomer, which generates chiral polyurea microcapsules containing magnetic nanoparticles within their cores. The microcapsules generated from the process are then utilized to selectively adsorb either the R or S enantiomer of tryptophan (Trp) from a racemic mixture that is dissolved in water, in order to evaluate their chiral recognition capabilities. During the experiments, the magnetically separable chiral poly(ionic liquid) microcapsules, which incorporated either the R or S isomer of chiral bis(mandelato)borate, exhibited exceptional enantioselective adsorption performance. Thus, the chiral polymeric microcapsules embedded with the R-isomer of the bis(mandelato)borate anion demonstrated significant selectivity for adsorbing L-Trp, yielding a mixture with 70% enantiomeric excess after 96 h. In contrast, microcapsules containing the S-isomer of the bis(mandelato)borate anion preferentially adsorbed D-Trp, achieving an enantiomeric excess of 73% after 48 h. Full article

Although various degradable gel materials have been developed for temporary plugging in oil fields, they often degrade too quickly in high-temperature environments. To address this issue, an unstable crosslinker was synthesized to prepare a high-temperature degradable gel. This gel does not degrade excessively fast at high temperatures. Temperature and crosslinker concentration are the primary factors influencing gel degradation time, followed by monomer and initiator concentrations. Increased temperature and decreased crosslinker concentration both reduce degradation time, which can be adjusted within the range of 90–130 °C by varying the crosslinker concentration. The molecular structure and thermal stability of the degradable gel were analyzed using FTIR, ¹³C NMR, and TG. Furthermore, the viscoelastic properties, compressive performance, plugging performance, and core damage performance of the gel were evaluated. Within the test range of 0.1–1000 Pa, the storage modulus is higher than the loss modulus. The gel prepared at 130 °C exhibited a compressive stress of 0.25 MPa at 50% strain. The plugging pressure of the gel in sand-filled tubes with varying permeabilities (538.2–2794.1 mD) exceeded 15 MPa while maintaining a core damage rate below 5%. SEM analysis indicated that the degradation mechanism of the gel may involve the collapse of its three-dimensional network structure due to the hydrolysis of amide groups in the crosslinker. The viscosity of the degradation liquid was below 11 mPa·s, enabling it to be brought back to the surface with the formation fluid without the need for further breaking operations. Full article

Ultraviolet (UV) curing is an efficient and environmentally friendly curing method. In this paper, UV-cured polyurethane acrylates (PUAs) were investigated as potential military coatings to serve as barriers against chemical warfare agents (CWAs). Seven UV-cured PUA coatings were formulated utilizing hydroxyethyl methacrylate-capped hexamethylene diisocyanate trimer (HEMA-Htri) and trimethylolpropane triacrylate-capped polycarbonate prepolymer (PETA-PCDL) as the PUA monomers. Isobornyl acrylate (IBOA) and triethyleneglycol divinyl ether (DVE-3) were employed as reactive diluents. Gas chromatography was utilized to investigate the constitutive relationships between the structures of the PUA coatings and their protective properties against simulant agents for CWAs, including dimethyl methylphosphonate (DMMP), a nerve agent simulant, and 2-chloroethyl ethyl sulfide (CEES), a mustard simulant. The glass transition temperature (T_g) and crosslinking density (υ_e) of PUAs were found to be crucial factors affecting their ability to serve as barriers against CWAs. The incorporation of IBOA units led to enhanced T_g and barrier performance of the PUAs, resulting in a DMMP retention of less than 0.5% and nearly 0 retention of CEES. However, an excessive introduction of polycarbonate chains decreased the υ_e and barrier performance of the PUAs. These findings may offer valuable insights for enhancing the protection of UV-cured PU coatings against CWAs. Full article