Reaction Of Isocyanate Research Articles

Field Performance of Asphalt Mixture Modified with Reactive Isocyanate Based Modifier

The reactive isocyanate-based modifier chemically reacts with asphalt components, overcoming the issues of increased viscosity and phase separation encountered with conventional modified binders. It can be used to modify binders to meet the highest performance grades currently specified by state highway agencies. This project aimed to demonstrate the constructability of an asphalt mixture modified with the reactive isocyanate-based modifier in the field and compare its performance with that of a control mixture. The project involved milling an approximately 5.0-cm (2-in) thick surface layer of two 30.5-m (100-foot) sections with similar foundation support. One section was resurfaced with a reactive isocyanate-modified mixture and the other with a conventional SBS-modified mix. The mixtures have shown no significant difference in field performance and laboratory performance test results. This study has provided insights into the field applicability of reactive isocyanate-based modifiers in asphalt mixtures, facilitating the ongoing efforts to develop durable road surfaces.

Effect of NaOH etching and oxygen plasma treatments on surface characteristics and their potential to activate micro-arc oxidized TiO2 coatings

Activation treatments such as NaOH etching or O2 plasma can play an essential role in surface conjugation of titanium with biomolecules, providing a better interaction at the bone-implant interface. However, their application on complex titanium dioxide (TiO2) surfaces is still not explored. In this contribution, bioactive and porous TiO2 coatings produced by micro-arc oxidation (MAO) were treated with NaOH etching or O2 plasma and then placed in contact with a reactive isocyanate test compound to evaluate the potential of molecule conjugation. Results suggested that O2 plasma treatment has only changed the surface chemistry of the coating through carbon contaminants removal, plasma-driven oxidation and generation of functional OH species, including reactive carboxyl groups. This chemical modification by plasma has made the surface superhydrophilic. After NaOH etching, the coating became rougher and also superhydrophilic, containing titanate structures doped with sodium and calcium on its surface and inside the inner pores. Upon reaction with butyl isocyanate, the O2 plasma-treated surfaces seem to better provide molecule conjugation, introducing characteristic conjugation bonds, and also making MAO coatings more hydrophobic due to the surface-terminated methyl chains from isocyanate. This proof-of-concept study has demonstrated the promising grafting potential given by O2 plasma on complex TiO2 surfaces.

Simple Route to Functional Cyclized/Knotted PManEMA-co-IMs: One-Pot RAFT/Hydroxyl–Isocyanate Reaction

Simple Route to Functional Cyclized/Knotted PManEMA-<i>co</i>-IMs: One-Pot RAFT/Hydroxyl–Isocyanate Reaction

Synthesis of isocyanate containing cryogels for fast (bio)molecular immobilization.

Cryogels containing isocyanate reactive groups were synthesized via photopolymerization of 2-isocyanoethyl methacrylate (ICEMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA). By changing the PEGMEMA and ICEMA ratios, cryogel series with varying ratios of reactive isocyanate groups were successfully prepared. The cryogels were characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, scanning electron microscope, and rheometry. To demonstrate that molecules containing amine groups can be immobilized onto synthesized cryogels through isocyanate-amine reactions, the cryogels were conjugated with 4-(trifluoromethyl)benzylamine (TFBA) and fluorescein amine (FLA) molecules, and the conjugations were confirmed through FTIR and fluorescence microscopy, respectively, for TFBA and FLA. Additionally, immobilization of fluorescein isothiocyanate conjugated albumin from bovine serum (FITC-BSA) as fluorescein-labeled model proteins was studied to illustrate that biomolecules can also be bound to the cryogels without any linker. It was shown that the amount of immobilized FITC-labeled model proteins can be controlled by adjusting the concentration of isocyanate reactive groups within the cryogel matrix, and this functionalization was confirmed by fluorescence microscope.

Hetero Cope-Type Hydroamination of Hetero-Allenes with Oximes Having Olefin Moieties Leading to Nitrones, Causing Intramolecular Cycloaddition.

Hetero-allenes such as isocyanates, isothiocyanates, and carbodiimides reacted with oxime having olefin moieties in the manner of hetero Cope-type hydroamination to generate N-modified nitrones, which underwent intramolecular cycloaddition to give intramolecular cycloadducts. Among them, the reaction of isocyanates with oximes proceeded at room temperature to provide the corresponding cycloadducts in very high yields. The efficiencies of these sequential cycloadditions were directly compared by competitive reactions. As a result, the order of reactivity to oxime 1a is isocyanate 2a, isothiocyanate 3a, and carbodiimide 6a. Theoretical studies were also conducted.

Construction of amine-rich coating utilizing amine curing reaction of triglycidyl isocyanate with triethylenetetramine on the surface of poly(styrene-divinylbenzene) microspheres for preparation of anion exchange stationary phase.

Epoxy resins, as important thermosetting polymers, exhibit excellent adhesion to various substrates. In view of this, reticulate coating of triglycidyl isocyanate with triethylenetetramine was introduced onto the surface of poly(styrene-divinylbenzene) utilizing amine curing reaction to obtain poly(styrene-divinylbenzene)@triglycidyl isocyanate-triethylenetetramine composite microspheres. The amino groups and epoxy groups of triglycidyl isocyanate-triethylenetetramine endowed poly(styrene-divinylbenzene) with good reactivity, which could be quaternized under mild conditions to obtain an anion exchange chromatographic stationary phase. The quaternized poly(styrene-divinylbenzene)@triglycidyl isocyanate-triethylenetetramine was characterized by scanning electron microscope, Fourier-transform infrared spectroscopy, N2 adsorption-desorption experiment, etal. The chromatographic performance of the customized column was evaluated by separating seven conventional anions, organic weak acids, and carbohydrates. Poly(styrene-divinylbenzene)@triglycidyl isocyanate-triethylenetetramine possesses the uniform size of poly(styrene-divinylbenzene) microspheres and good reactivity of triglycidyl isocyanate-triethylenetetramine, which offers a flexible strategy for the preparation of anion exchange stationary phase. The column exhibits excellent chemical and mechanical stability and chromatographic performance. Finally, the column was successfully applied for the determination of nitrite in pickles.

A clinical comparative study on carbamylated haemoglobin as a surrogate marker to differentiate acute kidney injury from chronic kidney disease.

Carbamylated haemoglobin is the result of reaction of isocyanate with N-terminal valine residues of the α and β chains of haemoglobin. Carbamylated haemoglobin concentration is dependent on the degree and duration of uraemia and thus may potentially serve as a marker to differentiate acute kidney injury (AKI) and chronic kidney disease (CKD). A hospital-based prospective clinical comparative study was conducted in an urban tertiary medical care centre. Carbamylated haemoglobin was estimated in a total of 60 patients, 30 each of chronic kidney disease and acute kidney injury. The comparison of the carbamylated haemoglobin levels among the CKD and AKI groups was done using Mann-Whitney test. The mean value of carbamylated haemoglobin among the CKD group was 240.71 ± 75.64 μgVH/g, whereas among the AKI group, it was 67.15 ± 17.05 μgVH/g. These values are statistically significant with P < 0.001. Carbamylated haemoglobin values were elevated in relation to renal dysfunction, and it significantly correlated with chronicity of kidney disease. Mean CarHb among the CKD group was significantly high in comparison to the AKI group with statistical significance, with a P value of <0.001. It was significantly attributed in this study that carbamylated haemoglobin >100 μgVH/g is diagnostic of CKD and a value <100 μgVH/g is diagnostic of AKI. Thus, in this study, it can be concluded that carbamylated haemoglobin is a useful marker to differentiate AKI from CKD.

Valorization of hemicellulose waste streams for moisture barrier coatings and hydrophobic films

Replacing plastics with renewable and environmentally friendly substitutes is becoming ever more critical as we begin to realize the consequences of their negative impacts on the environment. Plant polysaccharides are the most abundant biopolymers on Earth, and hemicelluloses like xylan that are enriched in many agro-industrial waste streams have vast potential as eco-friendly building blocks for polymer science and engineering. However, xylan is one of the less studied natural polymers for applications that are relevant to the synthetic plastics and polymeric materials markets. Hemicellulose isolated from viscose and Lyocell fiber mills is largely seen as a waste product due to difficulties arising from the potential for structural heterogeneity and its lack of solubility after enrichment. In this work, we developed a strategy to valorize hemicellulose by functionalization with octyl isocyanate to achieve solubility and thermoplastic/hydrophobic properties. Xylan isolated from dissolving pulp waste streams was successfully functionalized with octyl isocyanate in DMSO at an estimated 79% hydroxyl conversion. Reaction parameters, including temperature, time, and stoichiometry were optimized for each reaction. The resultant carbamates of xylan oligo- and monosaccharides have good solubility in chloroform and impressive hydrophobic film forming properties yet retain the composability properties desired for renewable materials that are envisioned to enter the circular bioeconomy. Functionalization of xylan with an aliphatic chain through formation of an aliphatic carbamate is not expected to harbor the same toxicity or carcinogenic characteristics as the reactive isocyanate it is derived from, and thus should not inherently restrict these materials for use in diverse packaging applications. These modified physical properties show that xylan from agro-industrial waste streams has considerable potential to replace petroleum-based feedstocks in the existing packaging industry. In the future, we will continue to further develop strategies for valorization of these materials.Graphical

Innovative Approach to Chiral Polyurethanes: Asymmetric Copolymerization with Isocyanates.

The introduction of nitrogen-containing functional groups to chiral polymer backbones enables the tailoring of physical properties and offers opportunities for further post-polymerization modification. However, the substrate scope of such polymers is extremely limited because monomers having nitrogen-containing groups can change coordination state with respect to the metal centers, thus decreasing the activity and enantioselectivity and even poisoning the catalyst completely. In this paper, we report our attempts to carry out the asymmetric copolymerization of meso-epoxide with highly reactive isocyanates. In particular, we found that biphenol-linked bimetallic Co(III) complexes with multiple chiral centers are very efficient in catalyzing this asymmetric copolymerization reaction, affording optically active polyurethanes with a completely alternating nature and a high enantioselectivity of up to 94% ee. Crucially, we identified that the steric hindrance at the phenolate ortho position of the ligand strongly influences the catalytic activity and product enantioselectivity. In addition, density functional theory calculations revealed that the highly sterically bulky substituents change the mechanism from bimetallic to monometallic, and result in the unexpected inversion of the chiral induction direction. Moreover, the high stereoregularity of the produced polyurethanes enhances their thermal stability. This study offers a versatile methodology for the synthesis of chiral polymers containing nitrogen functionalities.

Innovative Approach to Chiral Polyurethanes: Asymmetric Copolymerization with Isocyanates

AbstractThe introduction of nitrogen‐containing functional groups to chiral polymer backbones enables the tailoring of physical properties and offers opportunities for further post‐polymerization modification. However, the substrate scope of such polymers is extremely limited because monomers having nitrogen‐containing groups can change coordination state with respect to the metal centers, thus decreasing the activity and enantioselectivity and even poisoning the catalyst completely. In this paper, we report our attempts to carry out the asymmetric copolymerization of meso‐epoxide with highly reactive isocyanates. In particular, we found that biphenol‐linked bimetallic Co(III) complexes with multiple chiral centers are very efficient in catalyzing this asymmetric copolymerization reaction, affording optically active polyurethanes with a completely alternating nature and a high enantioselectivity of up to 94 % ee. Crucially, we identified that the steric hindrance at the phenolate ortho position of the ligand strongly influences the catalytic activity and product enantioselectivity. In addition, density functional theory calculations revealed that the highly sterically bulky substituents change the mechanism from bimetallic to monometallic, and result in the unexpected inversion of the chiral induction direction. Moreover, the high stereoregularity of the produced polyurethanes enhances their thermal stability, and they can be selectively decomposed into oxazolidinones. This study offers a versatile methodology for the synthesis of chiral polymers containing nitrogen functionalities.

Urethane Synthesis in the Presence of Organic Acid Catalysts-A Computational Study.

A general mechanism for catalytic urethane formation in the presence of acid catalysts, dimethyl hydrogen phosphate (DMHP), methanesulfonic acid (MSA), and trifluoromethanesulfonic acid (TFMSA), has been studied using theoretical methods. The reaction of phenyl isocyanate (PhNCO) and butan-1-ol (BuOH) has been selected to describe the energetic and structural features of the catalyst-free urethane formation. The catalytic activities of DMHP, MSA, and TFMSA have been compared by adding them to the PhNCO-BuOH model system. The thermodynamic properties of the reactions were computed by using the G3MP2BHandHLYP composite method. It was revealed that in the presence of trifluoromethanesulfonic acid, the activation energy was the lowest within the studied set of catalysts. The achieved results indicate that acids can be successfully employed in urethane synthesis and the mechanism was described.

In-situ reaction modification of isocyanate derivatives with hole-transport units on perovskite film surface for efficient and stable solar cells

FAPbI3 perovskite solar cells (PSCs) have attracted widespread research attention. The interfacial properties play a crucial role in perovskite defect passivation and interfacial carrier transport, significantly influencing the power conversion efficiency (PCE) and stability of devices. Here, a novel interface modification strategy of in-situ reaction on perovskite surface is proposed. A molecule N,N′-bis(4-isocyanatophenyl)-N,N′-di-p-tolyl-[1,1′-biphenyl]-4,4′-diamine (TPD-NCO), involving a hole-transporting unit TPD was synthesized. The highly reactive isocyanate (NCO) groups addition-reacted with formamidine ions (FA+) from the FAPbI3 surface, forming urea with firm covalent bonds. The resulting stable modification smoothened the interface, and its urea groups coordinated with Pb2+ and formed hydrogen bonds with I-, thereby passivating the surface defects and inhibiting ion migration. Moreover, the hole-transporting units were firstly anchored through this covalent modification as a p-type dopant to lower the interface energy barrier for hole extraction. The PCE of target devices increased from 22.82% to 24.46%, which also remained 93% for 5460 h under high humidity (65% RH), 87% for 1060 h under 75 °C, and 77% for 420 h under maximum power point (MPP) operation at 50 °C, indicating both excellent efficiency and long-term stabilities. This work displays the value of both firm and hole-conductive features in in-situ reactive interface modification.

Energetic Nitrate-Based Polymer-Bonded Explosives Derived from Sustainable Aza-Michael Reactions.

A novel nontoxic method for processing energetic binder, namely, polyglycidyl nitrate (PGN), using Aza-Michael reactions for deriving high-performance explosive formulations is being reported. The polyol binders used in polymer-bonded explosives (PBX) including PGN are usually cross-linked using isocyanate leading to polyurethane (PU)-based cured solid networks. These reactions require mild reaction conditions and yield good mechanical properties for the PBX but remain challenging due to extraneous reactions of isocyanate resulting in defects in the cured blocks. In addition, the presence of nitrato groups in the vicinity of terminal hydroxyl groups of PGN results in the decuring of cross-linked urethane that affects the storage life of PBX, though PGN-based binder can provide an 18% improvement in the velocity of detonation of PBX at lower solid loadings of 70%. This prevents researchers from exploiting the major performance advantage of using PGN for PBX compositions. This article herein features a green and mild aza-Michael reaction for functional modification of PGN using readily available substrates and triethylene tetramine to form a cross-linked β-aminocarbonyl network. The methodology ensures a void-free, stable, cured network and offers an effective replacement for toxic cure chemistry currently employed for processing of PBX.

Self-healing epoxy coatings via microencapsulation of aromatic diisocyanate in lignin stabilized Pickering emulsions

Isocyanate-filled microcapsules are gaining increased attention for their role in developing self-healing materials, thereby reducing maintenance costs and increasing polymer durability. Nevertheless, microencapsulating highly reactive -NCO groups remains a challenging task in the literature. Likewise, considerable efforts have been directed towards developing polymers from renewable and biobased sources, which could also be applied to microcapsule synthesis. In this work, lignin, an abundant biopolymer, was used as a solid stabilizer for oil-in-water (O/W) interfaces, enabling the encapsulation of highly reactive isocyanate. Hybrid polyurethane/polyurea microcapsules containing reactive methylenediphenyl diisocyanate (MDI) were obtained via optimized O/W Pickering emulsions using lignin for system stabilization. This optimized process facilitated shell formation via the reaction of diisocyanate with lignin and water, eliminating the need for additional chain extenders. Scanning electron microscopy revealed the formation of spherical and rough microcapsules, while infrared spectroscopy confirmed the presence of residual free -NCO groups, indicating effective encapsulation of MDI. Additionally, a core -NCO concentration of 11 wt% was confirmed by titration. The microcapsules were further assessed as components in self-healing epoxy coatings. Their incorporation resulted in the retardation of corrosion on a low carbon steel panel after 72 h of submersion in a saline solution. Electrochemical impedance spectroscopy (EIS) confirmed a significant increase of approximated 620% in impedance modulus after 83 days of immersion in a 3.5 wt% NaCl solution, compared to the neat epoxy coating. These findings suggest a promising technological application of this material for the advancement of self-healing epoxy-based coatings and composites.

Direct additive-free N-formylation and N-acylation of anilines and synthesis of urea derivatives using green, efficient, and reusable deep eutectic solvent ([ChCl][ZnCl2]2)

In the current report, we introduce a simple, mild efficient and green protocol for N-formylation and N-acetylation of anilines using formamide, formic acid, and acetic acid as inexpensive, nontoxic, and easily available starting materials just with heating along stirring in [ChCl][ZnCl2]2 as a durable, reusable deep eutectic solvent (DES), which acts as a dual catalyst and solvent system to produce a wide range of formanilides and acetanilides. Also, a variety of unsymmetrical urea derivatives were synthesized by the reaction of phenyl isocyanate with a range of amine compounds using this benign DES in high to excellent yields. [ChCl][ZnCl2]2 showed good recycling and reusability up to four runs without considerable loss of its catalytic activity.

Reactions of Heteroallenes with Salan-based Ti(IV) Complexes: A Joint Experimental and Computational Study.

The reaction of Ti(NMe2)4 with the salan ligand precursor H2N2O2H2 led to the formation of [(L*)Ti(NHMe2)2] (L*=N2O2 4-) that forms [(H2N2O2)TiCl2] upon reaction with two equiv. of Me3SiCl. [(L*)Ti(py)2] was obtained from the reaction of [Ti(NtBu)Cl2(py)3] with the sodium salt H2N2O2Na2. Treatment of [(L*)Ti(NHMe2)2] with two equiv. of tBuNCO led to the insertion of the isocyanate molecules into the Ti-Nsalan bonds with the formation of [{L*(N(tBu)CO)2}Ti]. Conversely, the reaction of [(H2N2O2)Ti(OiPr)2] with two equiv. of tBuNCO led to the insertion of one isocyanate molecule into a Ti-Nsalan bond with the formation of [{(HN2O2)(N(tBu)CO)}Ti(OiPr)]. Computational studies were performed to gain insight into the reactivity of isocyanates with salan-based Ti(IV) complexes.

Relief of Residual Stress in Bulk Thermosets in the Glassy State by Local Bond Exchange.

The covalently cross-linked network gives thermosets superior thermal, mechanical, and electrical properties, which, however, squarely makes the large residual stress that is inevitably induced during preparation hardly relieved in the glassy state. In this work, an incredible reduction in residual stress is successfully achieved in bulk thermosets in the glassy state through introducing highly dynamic thiocarbamate bonds by "click" reactions of thiols and isocyanates. Due to the excellent dynamic behaviors of thiocarbamate bonds, local network rearrangement is achieved through thermal stimulation, while the strong 3D cross-linked network is well maintained. Ultimately, a decrease by 44% in residual stress is detected by simply annealing samples at 30°C below glass transition temperature (Tg), during which they could well maintain more than 98.4% of the storage modulus. After the annealing, more uniform residual stress distribution is also observed, showing a 32% decline in sample standard deviation. However, the residual stress of epoxy resin, a typical thermoset as a reference, changes little even after annealing at Tg. The results prove it a feasible strategy to reduce residual stress in bulk thermosets in the glassy state by introducing proper dynamic covalent bonds.

Experimental and Theoretical Studies on the Reactions of Aliphatic Imines with Isocyanates.

In the context of a project aiming at the replacement of the 3-substituted β-lactam ring in classical β-lactam antibiotics by an N(3)-acyl-1,3-diazetidinone moiety, we have investigated the reaction of isocyanates with imines derived from allyl glycinate and differently substituted propionaldehydes. Imines of aromatic aldehydes with anilines have been reported to react with acyl isocyanates to give 1,3-diazetidinones or 2,3-dihydro-4H-1,3,5-oxadiazin-4-ones, via [2+2] or [4+2] cycloaddition, respectively. However, neither of these products was formed with imines derived from allyl glycinate and 2-(mono)methyl propionaldehydes. α,α-Dimethylation of the imine enabled the [4+2] cycloaddition pathway, but the desired 1,3-diazetidinone products were not observed. Surprisingly, the imines obtained from thioesters of 2,2-dimethyl 3-oxo propionic acid reacted with aryl isocyanates or with benzyl isocyanate to give 5,5-dimethyl-2,4-dioxo-6-(aryl-/alkylthio)tetrahydropyrimidines, via thiol displacement and re-addition to a putative six-membered iminium intermediate. These experimental results obtained for the reactions could be rationalized by DFT calculations. In addition, we have shown that N(3)-acyl-1,3-diazetidinone and 2,3-dihydro-4H-1,3,5-oxadiazin-4-one products can be distinguished based on experimental IR data in combination with theoretical reference spectra employing the IR spectra alignment (IRSA) algorithm. This discrimination was not possible by means of 1 H, 13 C, or 15 N NMR spectroscopy.

Syntheses of 3H-1,2,4-triazol-3-ones by copper-promoted oxidative N–N bond formation of amidines with isocyanates

A copper-promoted [3 + 2] annulation reaction of amidine hydrochlorides and isocyanates for the synthesis of 3H-1,2,4-triazol-3-ones is presented.

Effect of morpholine, and 4-methylmorpholine on urethane formation: a computational study

A theoretical study of urethane formation through the reaction of phenyl isocyanate and butan-1-ol was carried out, without and in the presence of morpholine, and 4-methylmorpholine catalysts. The reaction with and without catalysts was studied at BHandHLYP/6-31G(d) and G3MP2BHandHLYP levels of theories. The reaction mechanism in the presence of catalysts differs significantly from the catalyst-free case and includes seven steps. The catalyst-free system was investigated along with the catalytic process, the geometries were optimized, and the corresponding thermodynamic properties were calculated. Calculated reactant complexes were compared with crystal structures of morpholine, and 4-methylmorpholine complexed with diols found in the literature. The structures were strikingly similar and thus, the validity of the proposed and studied general organocatalytic reaction mechanism was partially verified. Meanwhile, an irregularity in the energy profile occurred due to the zwitterionic nature of an intermediate. To handle the irregularity, a correction was implemented which handles the appearance of a zwitterionic structure and the corresponding energetic properties. The results showed that morpholine is less effective catalyst compared to 4-methylmorpholine, which can be associated with the difference in their PA (1523.95 and 963.07 kJ/mol, respectively). The current results prove the important role of amine catalysts in urethane synthesis which can be applied in polyurethane catalyst design and development.