Aromatic Isocyanates Research Articles

Yellow resistant photosensitive resin for digital light processing 3D printing

ABSTRACTDigital light processing (DLP) has been studied and developed in the field of three‐dimensional (3D) printing in recent years due to its fast curing rate and high resolution. To reduce the cost and viscosity of the resin system, the aromatic polyurethane acrylates (PUAs) were used as oligomer. The matrix resin called PUH2 consists of oligomers (PUA, bisphenol A polyoxyethylene ether dimethyl acrylate) and active diluents (hydroxyethyl acrylate, hydroxyethyl methacrylate). However, the photosensitive resin containing aromatic isocyanate groups was easily yellowed under ultraviolet light. In this article, we developed a resin for DLP 3D printing with yellowing resistance, excellent mechanical properties and high heat resistance. The optimal ratio of 3DP‐PUH2 resin was PUH2/TPO/RYOJI‐292/dye/nanosilica = 100/5/0.4/0.01/0.1, and its viscosity was 500 cp, which is suitable for DLP 3D printing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48369.

Computing a cleaner polyurethane synthesis

Polyurethanes are found in many everyday products, including footwear and furniture, but their synthesis leaves something to be desired. Manufacturers use reactive N,N-dimethyl amine catalysts that are incorporated into the material and give off toxic formaldehyde over its lifetime. Now, Mikko Muuronen, Peter Deglmann, and Željko Tomovic of BASF have used a computational model and experiments to evaluate alternative catalysts, identifying candidates that do not produce formaldehyde (J. Org. Chem. 2019, DOI: 10.1021/acs.joc.9b01319). Manufacturers produce polyurethanes via the reaction between an aromatic isocyanate compound and a polyol catalyzed by a tertiary amine. The methyl groups in the standard N,N-dimethyl amine catalysts can break down, producing formaldehyde. The researchers thought that alternative amines lacking methyl substituents could avoid this issue. The team modeled this reaction with the N,N-dimethyl amine and six alternative amine catalysts with longer alkyl substituents and various rin...

Hierarchical Machine Learning Model for Mechanical Property Predictions of Polyurethane Elastomers From Small Datasets

Polyurethanes are a broad class of material that finds application in coatings, foams, and solid elastomers. The urethane chemistry allows a diversity of monomers to be used, and prediction of mechanical properties, which are determined by complex interplay between monomer chemistry and chain architecture, is an unresolved challenge. Urethanes are based on aromatic or cyclic isocyanates and linear or branched polyols, and polymerization results in linear chains for bifunctional monomers or branched chains for multifunctional monomers. Strong intermolecular interactions between aromatic groups result in the formation of hard-segment domains that generate physical crosslinks between disorganized rubbery domains and anchor the material microstructure, contributing to resistance to deformation. Here, a general hierarchical machine learning (HML) model for predicting the stress-at-break, strain-at-break, and Tan δ for thermoplastic and thermoset polyurethanes is presented. The algorithm was trained on a library of 18 polymers with different diisocyanates, bifunctional or trifunctional polyols, and NCO:OH index. HML reduces data requirements through robust embedding of domain knowledge and surrogate data in a middle layer that bridges input variables (composition) and output responses (mechanical properties). In this work, the middle layer included information on overall polymer composition, predictions of chain architecture derived from Monte Carlo simulations of polymerization, information on interchain interactions from empirically derived molecular potentials and shifts in infrared (IR) spectroscopy absorbances. The HML predictions are shown to be more accurate than those from a Random Forest model directly relating composition and properties, suggesting that embedding domain knowledge provides significant advantages in predicting the properties of complex material systems based on small datasets.

Cationic Polymerization of (3‐Aminopropyl)‐tris‐furfuryloxysilane Derivatives—a New Strategy for Complex Hybrid Material Synthesis

AbstractThe trifunctional (3‐aminopropyl)‐tris‐furfuryloxysilane monomer (1) is able to undergo both twin polymerization and reaction with electrophilic compounds such as isocyanates. 1 can be readily synthesized from 3‐aminopropyptrimethoxysilane (APTMS) and furfuryl alcohol (FA). The reaction of 1 with three different aromatic isocyanates, namely phenyl isocyanate, diphenylmethane‐4,4′‐diisocyanate (MDI), and a prepolymer consisting of MDI end‐capped polytetramethylene ether glycole (PTMEG), to the corresponding substituted urea derivatives is presented. Three urea derivatives 1‐phenyl‐3‐(3‐tris‐furfuryloxysilyl)propylurea (2), diphenylmethan‐4,4′‐bis[3(tris‐furfuryloxysilyl)propyl]urea (3), bis[3(tris‐furfuryloxysilyl)‐propyl]urea‐capped PTMEG‐MDI‐prepolymer (4) as well as 1 were polymerized to multicomponent organic/inorganic hybrid materials in a one step procedure using methane sulfonic acid as catalyst. The simultaneous formations of poly furfuryl alcohol and polysiloxane networks within the hybrid material are proven by means of solid‐state NMR spectroscopic measurements. The homogeneous distribution of silicon within the solidified hybrid materials is analyzed by scanning electron microscopy, energy dispersive X‐ray spectroscopy, and high‐angle annular dark field‐scanning transmission electron microscopy (HAADF)‐STEM. Homogeneous nanostructured hybrid materials with silicon cluster sizes in the range of 2 nm have been obtained by polymerization of the urea derivatives 2, 3, and 4.

Synthesis, characterization and crystal structure of heterocyclic tetrahydropyrido[4′,3′:4,5]thieno[2,3-d]pyrimidinone derivatives via sequential aza-Wittig/base catalyzed cyclization

Seventeen examples of 7-Benzyl-5,6,7,8-tetrahydropyrido [4′,3′:4,5]thieno [2,3-d]pyrimidin-4(3H) -ones were synthesized by base catalyzed reactions of nucleophilic reagents (aliphatic amines, alcohols or phenols) with carbodiimides 3, which in turn were obtained by the aza-Wittig reaction of iminophosphorane 2 with aromatic isocyanates. The compounds were fully characterized by analytical and spectroscopic techniques (FT-IR, 1H NMR, 13C NMR and MS). Crystal structure determination of three tetrahydropyrido [4′,3':4,5]thieno [2,3-d]pyrimidinone derivatives has been undertaken in order to better understanding the influence of structural modifications upon overall molecular geometry and conformation. 3D supramolecular architectures are formed in the crystals by self-assembly of the molecules via stacking interactions and various hydrogen bonds. Meanwhile, crystal structure of a guanidine intermediate 4a was characterized in order to proclaim the reaction mechanism of the base catalyzed intramolecular cycloaddition.

High-efficiency self-repairing anticorrosion coatings with controlled assembly microcapsules

Based on the principle of emulsion technology and self-assembly of materials, aromatic isocyanate derivatives easily reacted with polyols to form polyurethanes, and nonaromatic isocyanate derivatives were responsible for generating the capsule core of the self-healing microcapsules. In this paper, epoxy resin-based self-healing smart anticorrosion coatings with different types of microcapsules were prepared. The cores were IPDI/TMP–IPDI/DiPE–IPDI. The optimal conditions for the preparation of self-repairing microcapsules to achieve controlled assembly of a microcapsule material structure were determined. We set up a test model, incorporating thermal analysis, depression repair level calculation, salt spray corrosion tests, adhesion tests, and other indicators of application performance. The corrosion resistance was in the order: DiPE–IPDI > TMP–IPDI > IPDI > pure epoxy. The experimental results showed a self-healing efficiency of more than 80% for cores of DiPE–IPDI. Taking into account the overall properties, the best-quality coatings contained approximately 5% microcapsules of DiPE–IPDI.

Derivatives of Azidocinnamic Acid in the Synthesis of 2-Amino-4-Arylidene-1H-Imidazol-5(4H)-Ones

A method for the synthesis of 2-amino-4-arylidene-1H-imidazol-5(4H)-ones is proposed based on the reaction of various aromatic isocyanates with phosphazenes derived from azidocinnamic acid amides. The spectral-luminescent properties of the obtained compounds were studied. The products were shown to possess the (Z)-configuration with the help of two-dimensional spectroscopy.

Synthesis of N′-phenyl-N-hydroxyureas and investigation of their inhibitory activities on human carbonic anhydrases

A series of N′-phenyl-N-hydroxyureas has been prepared by reacting hydroxylamine with aromatic isocyanates. These compounds were investigated as inhibitors of human carbonic anhydrases (hCAs, EC 4.2.1.1), considering four physiologically relevant isoforms, the cytosolic isoforms hCA I and II, and tumor associated, transmembrane isoforms hCA IX and XII. The new compounds reported here did not inhibit the widespread cytosolic isoforms hCA I and II, but they inhibited the tumor associated isoforms with interesting potencies. The most effective inhibitors showed KIs ranging between 72.8 and 78.9 nM against hCA IX and between 6.9 and 7.2 against hCA XII, making them of interest as candidates for antitumor studies.

Insight into the mechanism of the catalysis of urethane formation by organotin(IV) dicarboxylate

The field of surface coatings is an area of urethane technology and is rapidly gaining popularity due to ongoing performance improvements. Key to this is improved control of the catalysis of the urethane reaction obtained through an increased understanding of the catalysis mechanisms involved. Organotin dicarboxylates are industrially important catalysts in the formation of urethanes by reacting an isocyanate with an alcohol. This catalyst works for both aliphatic and aromatic isocyanates; however in industrial applications the catalyst is less important for aromatic isocyanates than aliphatic isocyanates. It has already been shown from our earlier investigations of catalysis mechanisms that organotin dicarboxylate catalysis of aromatic isocyanates is different to the mechanism for aliphatic isocyanates for urethane formation in non-polar media. In the present study, we further confirm these results using thermochemical data, which show that for organotin dicarboxylate catalysis of isocyanates in non-polar media, the carboxylate ligand of the catalyst contributes to catalysis of aliphatic isocyanates whereas the ligand has no effect for catalysis of aromatic isocyanates. The new knowledge was used to explain the behavior of pre-polymer when synthesized using different organotin compounds as catalyst with respect to viscosity increase in storage. These data will be useful in the manufacture of pre-polymers for 1 component (1 K) moisture cure urethane systems.

A Solvent-Free and Scalable Method To Prepare Soybean-Oil-Based Polyols by Thiol–Ene Photo-Click Reaction and Biobased Polyurethanes Therefrom

A solvent-free and scalable method was developed for the preparation of soybean-oil-based polyols by a thiol–ene photo-click reaction with a homemade photochemical reactor. The effect of reaction parameters, including photoinitiators, reaction time, molar ratios of thiols to carbon–carbon double bonds, and power of the mercury lamp, on the structures of the resulting polyols was investigated. The mechanism of the thiol–ene photo-click reaction was also discussed. On the basis of these novel polyols, several polyurethanes were prepared using different diisocyanates (aliphatic, cycloaliphatic, and aromatic isocyanate) and characterized. The resulting polyurethane films possess good performance, including the highest glass transition temperature of 41.3 °C, tensile strength of 15.7 MPa, and elongation at break of 471.0%.

Influence of aliphatic and aromatic isocyanates on the properties of poly(ether ester) polyol based PU adhesive system

This study has been conducted with an emphasis to develop a biobased polyol from canola oil by transesterification reaction followed by epoxidation and ring opening reaction with an intention to insert hydroxyl group at unsaturation sites. The products obtained were characterized by nuclear magnetic resonance and FTIR spectroscopy for structural analysis and to determine the extent of reaction. Furthur, the studies have been conducted on different Polyurethane (PU) adhesives obtained by reacting this resulted canola oil based polyether‐ester polyol and various kinds of aliphatic or aromatic diisocyanates commercially available, i.e., Methylenediphenyldiisocyanate (MDI), Toulenediisocyanate (TDI), Isophoronediisocyanate (IPDI), Hexamethylenediisocyanate (HMDI) with a purpose to examine their influence on adhesive properties such as green strength, curing time, gel time, lap shear strength. The properties of resulted polyurethanes had shown considerable (or prominent) variation in their behavior particularly in terms of thermal stability, adhesion strength, corrosion resistance, etc. The synthesized adhesive showed much better performance as compared to commercially available adhesive formulation under different conditions of testing. The thermal stability of PU adhesive formulation were analyzed and compared by thermogravimetric analysis. POLYM. ENG. SCI., 58:112–117, 2018. © 2017 Society of Plastics Engineers

Pd(II)/Ag(I)-Promoted One-Pot Synthesis of Cyclic Ureas from (Hetero)Aromatic Amines and Isocyanates.

A simple and facile one-pot reaction has been developed to afford a diverse range of N,N'-disubstituted benzimidazolones and imidazopyridinones containing two differently substituted N atoms. A cooperative Pd(II)/Ag(I) system promotes the sequential addition/intramolecular C-H amidation reaction of (hetero)aromatic amines and isocyanates, leading to the formation of two C-N bonds. A mechanism involving radical intermediates generated by single-electron transfer (SET) in the presence of a Ag2CO3 oxidant and Pd(OAc)2 Lewis acid is proposed. This protocol offers an operationally easy, simple, and robust approach with the use of readily available starting materials, good functional group tolerance, and high efficiency.

Development of an Interception Glove Sampler for Skin Exposures to Aromatic Isocyanates

Skin is an important exposure route for isocyanate chemicals and contributes to systemic sensitization. Methods for assessing skin exposure are currently limited and generally rely upon removal (e.g. tape-strip) techniques prone to underestimation. The aim of this study is to (i) develop and field test an interception-based hand exposure sampler to monitor potential skin exposure to isocyanates in the workplace, (ii) to develop an analytical method based on ultra-high-performance liquid chromatography-UV absorbance-tandem mass spectrometry (UHPLC-UV-MS/MS) for analyzing glove samples; and (iii) compare it with tape-stripping skin sampling method. Laboratory investigations assessed different glove materials/fabrics, methods for impregnating with 1-(9-anthracenylmethyl)piperazine (MAP) derivatizing agent, methylene diphenyl diisocyanate (MDI) uptake and recovery, and durability. Following use, gloves were dissected into sections corresponding to different spatial regions (finger, palm) and analyzed using a newly developed UHPLC-UV-MS/MS method capable of differentiating and quantitating different MDI isomers with high sensitivity. Performance of the glove sampler was further assessed in a pilot field study using six workers. A MAP-impregnated thin cotton glove sampler and UHPLC-UV-MS/MS analytical method for detecting MDI were successfully developed in laboratory studies. In subsequent field studies, a total of 384 samples from 14 glove pairs identified full-shift exposures ranged from 0.01 to 306 µg of 4,4'-MDI/worker for each hand. Surface area adjusted MDI values measured with the glove sampler (0.13-572ng MDI cm-2) were considerably higher (~400-fold) than values obtained with tape stripping. A glove sampler and a novel UHPLC-UV-MS/MS analytical method were developed to quantitatively measure MDI skin exposure. The novel interception technique overcomes inherent limitations of removal techniques for measuring isocyanate skin exposure and may be useful in exposure surveillance and future research on isocyanate's health risks.

Structural Aspects of Thermally Cleavable Adducts Derived from the Reaction of Imidazolines with Isocyanates

The reaction of isocyanates with substituted imidazolines and the thermally induced cleavage of the resulting adducts are presented. For this purpose, reactions of various isocyanates [ethyl isocyanate, p-methylphenyl isocyanate, phenyl isocyanate, p-(trifluoromethyl)phenyl isocyanate] with 1-alkylimidazoline derivatives have been studied as a function of the substituent at the 2-position of the imidazoline ring. Three equivalents of isocyanate react with one equivalent of 1-ethylimidazoline to give a stoichiometric well-defined adduct. However, 1-ethyl-2-isopropylimidazoline reacts with isocyanates at 0 °C in another way, with formation of 2:1 adducts which belong to the family of 1,3-diphenyltetrahydroimidazo[1,2-a][1,3,5]triazine-2,4(1H,3H)-diones. The reaction of 1-ethyl-2-methylimidazoline with aromatic isocyanates at 0 °C also leads to 2:1 adducts, in this case of a malonamide type, which can react at 60 °C with an additional isocyanate equivalent to give the known pyrimidinediones. Thermal analysis (TG-MS/DSC) and trapping reactions with nucleophilic reagents, such as diphenylamine, show the release of isocyanate during the thermally induced cleavage reaction. Thus, blocked isocyanates are available by the reaction of isocyanates with 1-ethylimidazoline or 1-ethyl-2-isopropylimidazoline.

Synthesis and antifungal activities of 3-alkyl substituted thieno[2,3-d]pyrimidinones

The 3-aryl substituted thieno[2,3-d]pyrimidinones 3 by sequential reaction of iminophosphorane 1, aromatic isocyanates and various nucleophiles (HY), found some compounds showed good antitumor and antibacterial activities. Meanwhile, aliphatic isocyanates were applied in the reaction to prepare 3-alkyl substituted thieno[2,3- d]pyrimidinones, but there are no reports of their antifungal activities. As a continuation of our research for new biologically active heterocycles, we herein wish to report a facile synthesis and antifungal activities of 3-alkyl substituted thieno[2,3-d]pyrimidinones 6 via easily accessible iminophosphorane 1. The growth inhibitory effect of one concentration (50mg/L) of compounds 6 against five fungus(Fusarium oxysporium, Rhizoctonia solani, Colletotrichum gossypii, Gibberella zeae and Dothiorella gregaria) in vitro was tested by the method of toxic medium. Compound 6d showed the best inhibition rate against Gibberella zeae with 85.68%.

Non-isocyanate route to amides and polyamides through reactions of aryl N-phenylcarbamates with carboxylic acids

In pursuit of green processes for synthesizing organic products and polymers, an efficient route of amide formation has been devised by reacting carbamates with carboxylic acids. Aryl N-phenylcarbamates were utilized as alternative reagents to replace aromatic isocyanates in amides and polyamides syntheses. The results showed that the high-yield of amide products can be produced from phospholene oxide-catalyzed reactions. This non-isocyanate route (NIR) resulted in amides with greater than 90 % amide selectivity and little urea or isocyanate by-product contaminants. The polyamides prepared from the subsequent reaction series between aryl N,N′-diphenyl biscarbamates and hexafluoroisopropylidene bis-benzoic acid (HFI-BBA) yielded soluble polyamides with high molecular weight and high thermal stability. Thus, aryl N-phenylcarbamates are considered as the viable intermediates for the green synthesis of amides or polyamides without using the toxic aromatic isocyanates.

Synthesis of Industrially Relevant Carbamates towards Isocyanates using Carbon Dioxide and Organotin(IV) Alkoxides

A straightforward phosgene-free synthesis of aromatic isocyanates and diisocyanates is disclosed. Theoretical investigations suggested that the insertion of carbon dioxide (CO2 ) by dialkyltin(IV) dialkoxides could be used to convert aromatic amines into aromatic mono- and dicarbamates. Here we show, that methyl phenylcarbamate (MPC) from aniline using organotin(IV) dimethoxide and CO2 can be formed in high yield of up to 92 %, experimentally corroborating the predictions of density functional theory (DFT) calculations. MPC was then separated from the tin oxide residues and converted into phenyl isocyanate. Furthermore, organotin(IV) alkoxides could be regenerated from the tin oxide residues and reused, paving the way for a continuous industrial process. Extension of the scope to the synthesis of diurethanes from toluene 2,4-diamine and 4,4'-methylenedianiline could potentially allow the efficient production of industrially relevant diisocyanates.

Synthesis of Oxazolidinones from Epoxides and Isocyanates Catalysed by Aluminium Heteroscorpionate Complexes

AbstractThe combination of an aluminium(heteroscorpionate) complex and tetrabutylammonium bromide acts as a highly efficient catalyst system for the synthesis of oxazolidinones from epoxides and isocyanates. Twenty two complexes were tested derived from a range of bispyrazole ligands and containing 1–3 aluminium atoms per complex. The optimal catalyst was found to be a bimetallic complex of a thioacetamidate ligand. Under the optimal reaction conditions (80 °C in toluene for 24 h using 5 mol % of both aluminium catalyst and tetrabutylammonium bromide co‐catalyst), six epoxides were reacted with six aromatic isocyanates, giving 25 oxazolidinones in moderate to excellent yields showing broad substrate scope. The regiochemistry of the reaction (to produce 3,4‐ or 3,5‐oxazolidinones) is controlled by the substrate with epoxide ring opening occurring preferentially at the less hindered end of the epoxide unless a substituent on the epoxide can stabilise a positive charge.

Biocomposites based on chemically modified cellulose fibers with renewable fatty‐acid‐based thermoplastic systems: Effect of different fiber treatments

ABSTRACTAdvanced biocomposites, based on binary and ternary systems, were developed with thermoplastic matrices such as thermoplastic polyurethane (TPU) and polyamide (DAPA) obtained from dimers of fatty acids, and cellulose fibers (CF). The CF were modified to display high interfacial adhesion and compatibility with the rather hydrophobic matrices. Different routes were considered such as grafting onto with prepolymers, or grafting from with aromatic isocyanate or fatty acid. An original approach of this work is to consider CF as a polyol with an equivalent hydroxyl index obtained by titration. In order to understand better the effect of each phase, the resulting modified CF were tested with neat TPU and DAPA matrices. The most promising fibers treatments were then tested with 80/20 and 50/50 wt %/wt % TPU/DAPA blends. Properties at the molecular and macromolecular scale were investigated. Improvement of the interfacial adhesion between the fibers and the polymers were observed. From the different grafting approaches tested, the best performing were the isocyanate‐terminated prepolymer and the silane‐terminated prepolymer modifications. In comparison with neat CF, modification with isocyanate‐terminated prepolymer improved threefold the storage and Young's modulus of TPU biocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43878.

Iminophosphoranes in Heterocyclic Synthesis: A Facile Synthesis of Pyrido[4,3‐D]Pyrimidine and Pyrido[4,3‐D][1,3]Oxazine Derivatives via Intermolecular aza‐Wittig Reactions

A novel series of pyrido[4,3‐d]pyrimidine and pyrido[4,3‐d][1,3]oxazine derivatives were synthesized via tandem aza‐Wittig and annulation reactions with the corresponding iminophosphoranes, aromatic isocyanate, and amines. All newly synthesized compounds were elucidated by considering the data of both elemental and spectral analysis.