Aliphatic Isocyanates Research Articles

ChemInform Abstract: A New Synthesis of Alkyl-N,N-dinitramines by Direct Nitration of Isocyanates.

Abstract A facile conversion of aliphatic isocyanates to N,N-dinitramines has been developed. An aliphatic isocyanate is treated with a mixture of nitronium fluoroborate and nitric acid in acetonitrile giving fair yields and simplifing the existing synthesis.

ChemInform Abstract: Aza Wittig-Type Reaction Between the Iminophosphorane Derived from 3- Amino-4-phenylthiazole-2(3H)-thione and Iso(thio)cyanates: Preparation of Mesoionic Thiazolo(2,3-b)-1,3,4-thiadiazoles and N,N- Bisheteroarylamines.

Abstract Aza Wittig-type reaction of iminophosphorane 1 derived from 3-amino-4-phenylthiazole-2(3H)-thione with several types of iso(thio)cyanates has been studied. The reaction of 1 with aromatic iso(thio)cyanates leads to thiazolo[2,3-b]-1,3,4-thiadiazoles 2 which display mesoionic character, whereas that with aliphatic isothiocyanates affords the betaines 3 . N,N′-Bisheteroarylguanidines 5 are obtained from the reaction of 1 with aliphatic isocyanates; further treatment of compounds 5 with @Tetrafluoroboric acid leads to N,N-bisheteroarylamines 8 . The reaction of 1 with acyl chlorides affords thiazolo[2,3-b]-1,2,4-thiadiazolium salts 12 .

ChemInform Abstract: An Efficient One-Pot Synthesis of Pyrrolo(4,3,2-ij)isoquinoline Derivatives by a Consecutive Aza-Wittig/Electrocyclic Ring Closure/ Intramolecular Acylation Process.

Iminophosphorane, ethyl 5-ethoxycarbonyl-2-methoxy-α-[(triphenylphosphoranylidene)amino]cinnamate (4) reacts with aliphatic and aromatic isocyanates in toluene at 170 o C to give directly the corresponding pyrrolo[4,3,2-if]isoquinolines 8 in moderate yields

Synthesis of 2,3,4-Tri-Substituted 3,4-Dihydroquinazolines via Tandem Nucleophilic Addition/Epoxy Ring-Opening Cyclization Methodology Using N-(2-Oxiranylphenyl)carbodiimides with Nucleophiles

N-(2-Oxiranylphenyl)carbodiimides, which were synthesized via an aza-Wittig reaction of the corresponding functionalized iminophosphoranes with aromatic and aliphatic isocyanates, underwent O-, S-, C-, or N-nucleophilic addition onto a cumulene, followed by an epoxy ring-opening cyclization with the newly formed NH-nucleophile in a one-pot reaction to furnish 2,3-disubstituted 4-(hydroxymethyl)-3,4-dihydroquinazolines in a highly stereospecific manner.

Dielectric Properties of Novel Polyurethane/Silica Nanowire Composites

An aliphatic isocyanate, polyether, polyol thermoplastic polyurethane, Tecoflex SG-85A, was solution processed with the varying amounts of silica nanowire. The dielectric permittivity (epsilon') and loss factor (epsilon") were measured via Dielectric Analysis (DEA) in the frequency range 1 Hz to 100 kHz and between the temperature -150 to 150 degrees C. The electric modulus formalism was used to reveal alpha, beta and conductivity relaxations. The activation energies for the relaxations are presented. Nanocomposites were also characterized by differential scanning calorimetry (DSC) to determine glass transition temperatures. The onset of decomposition temperature was measured by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites.

Objective Color Scale for the SWYPE Surface Sampling Technique Using Computerized Image Analysis Tools

Colorimetric SWYPE pads are useful tools for identifying unpolymerized aliphatic isocyanates on a variety of surfaces. This technique has been used in autobody shops to determine the presence of hexamethylene diisocyanate and other aliphatic isocyanates that are important constituents of many automotive coatings. SWYPEs have the advantage of being relatively inexpensive, rapid, and portable. The color change elicited by aliphatic isocyanates (from yellow to red) provides a visual indication of the extent of surface contamination. To quantify isocyanate contamination based on the colorimetric response, an objective color scale was developed for isocyanate loading. Sampled pads were digitized on a calibrated, portable flatbed scanner, and red-green-blue (RGB) histograms of SWYPE images were created. A calibration curve was created from a series of reference images derived from SWYPEs loaded with an isocyanate-containing product. The SWYPE RGB analysis allowed for quantification over a range of isocyanate loadings: from ∼0.01 to 24.0 μg/cm2, with reproducibility of >90%, accuracy >90%, and a surface extraction efficiency of >90%. RGB analysis exhibited a lower detection limit than visual scoring (∼3 μg versus ∼10 μg). The colorimetric response was cross validated with a high-performance liquid chromatography quantitative assay. When combined with RGB analysis, SWYPE colorimetric wipes represent a rapid and inexpensive method to assess objectively surface contamination with aliphatic isocyanates.

Polyurethane elastomers based on 1,3 and 1,4‐bis(isocyanatomethyl)cyclohexane

AbstractMost polyurethane elastomers in the market place are based on aromatic isocyanates. This is partially due to the higher cost of aliphatic isocyanates compared with aromatic isocyanates which are commonly used by the industry. However, more importantly, it has been the performance deficiency of polyurethane elastomers based on commercial aliphatic isocyanates that has significantly limited their use. Though aliphatic‐based polyurethane elastomers possess increased resistance to hydrolysis and thermal degradation in addition to greater light stability, these elastomers often experience a decrease in physical–mechanical properties when compared with aromatic isocyanate‐based materials. In this study, we investigated elastomers based on 1,3 and 1,4‐bis(isocyanatomethyl)cyclohexane, an experimental diisocyanate recently developed by The Dow Chemical Company. The physical properties of the elastomers are reported and discussed in comparison to similar elastomers prepared from commercially available aliphatic and aromatic isocyanates. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A New Approach to Studying Microcapsule Wall Growth Mechanisms

Polyurea microcapsules were prepared by sequential interfacial reaction of different aromatic and aliphatic isocyanates. The resulting composite capsule walls were studied using scanning transmission X-ray microscopy (STXM) to quantitatively map the distributions of the resulting aromatic and aliphatic polyureas across the capsule wall. Application of this method to both cross-linked and non-cross-linked polyurea capsules resulted in observation of different capsule wall growth mechanisms, depending mainly on the choice of monomers.

PREPARATION AND CHARACTERISTICS OF NOVEL HYPERBRANCHED PEU-BASED GEL POLYMER ELECTROLYTES

Gel polymer electrolytes (GPEs) based on hyperbranched poly (ether urethane) (PHEU) were prepared from the reaction of the hyperbranched polyether (PHEMO) with different diisocyanates in liquid electrolyte. The ionic conductivities and transference number of the GPEs were investigated by alternating current (AC) impedance and multi-potential steps. It is found that the ionic conductivities of GPEs were influenced by diisocyanate structure, lithium salt concentration and addition amount of liquid electrolyte. Sample PUM-0.5M-80% originated from 4, 4-diphenylmethane diisocyanate (MDI) as the hard segment shows the highest ionic conductivity of 2.41×10-3 Scm-1 at ambient temperature. The lithium ion transference number is 0.7. In addition, small molecules of liquid electrolyte were perfectly entrapped by polymer matrix, and liquid leakage in lithium ion battery was avoided. 5 . The hard segment provides good mechanical strength, while the soft segment improves the ionic conductivity. The rubbery soft segments can dissolve alkali metal salts, and help achieving high ion mobility, which originates from the interaction of the ether oxygen with the alkali metal ions. In the previous report 6 , the hyperbranched polyether (PHEMO) without stiff groups is selected as soft segment, as well as its amorphous state inherently derived from the hyperbranched molecular structure. Therefore, PHEMO is expected to improve the ionic conductivity of polymer electrolyte 7 . Due to their good mechanical properties, diisocyanates are chosen to act as hard segment domains contributing to the dimensional stability of the polymer electrolytes 8 . In this paper, GPEs based on PHEU were prepared with hyperbranched polyether (PHEMO) and diisocyanates in liquid electrolyte. Diisocyanates with different structures, such as aliphatic isocyanates of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), or aromatic isocyanates of 4, 4-diphenylmethane diisocyanate (MDI) and 2, 4-tolune diisocyanate (TDI) were served as hard segments, respectively. The effects of diisocyanate structure, lithium salt concentration and addition amount of electrolyte on the ionic conductivities of the as-prepared GPEs were discussed and compared.

Effect of isocyanate structure on deblocking and cure reaction of N-methylaniline-blocked diisocyanates and polyisocyanates

Two series of N-methylaniline-blocked isocyanates based on monomeric diisocyanates such as 4,4′-methylene bis(phenyl isocyanate), toluene-2,4-diisocyanate, isophorone diisocyanate and 1,6-diisocyanato hexane and their NCO terminated polyurethane prepolymer (polyisocyanates) were prepared and characterized thoroughly by FTIR, 1H NMR, 13C NMR and EI-Mass spectroscopic methods. The blocking reaction of N-methylaniline with aromatic isocyanates and aromatic polyisocyanates occur faster when compared to the aliphatic isocyanates. The deblocking reactions of blocked isocyanates were carried out under dynamic and isothermal conditions using hot-stage FTIR spectrophotometer. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate kinetics and thermodynamics parameters. Cure reactions of blocked isocyanates with hydroxyl-terminated polybutadiene were also followed to establish the structure–property relationship of the N-methylaniline-blocked isocyanates. The deblocking studies of blocked isocyanates reveal that the aromatic isocyanates undergo deblocking easily compared to aliphatic isocyanates. The rate of deblocking reaction of N-methylaniline-blocked aromatic polyisocyanates was found to be higher compared to N-methylaniline-blocked aromatic monomeric diisocyanate adducts. On the other hand, this trend was just reverse in the cure-reaction studies. The dissolution behavior of N-methylaniline-blocked isocyanates in Terathane-2000, polypropylene glycol-2000, polycaprolactone diol-2000 and hydroxyl-terminated polybutadiene-2500 was also studied and found that all adducts are soluble in these polyols.

Hydrogen bonding effects on aspartate ester reactions

Michael addition reactions were utilized to form AB2 type monomers and esterified to form polyaspartate esters (PASPE). FTIR and NMR spectroscopic methods indicate that a relatively linear architecture was produced that contrasts with an expected hyperbranched (HB) structure. Linear chains formed due to a reactivity difference between the hydrogen bonded (H-bonded) and non-H-bonded esters. The esterification reaction was directed toward the H-bonded ester as shown by 2D NMR correlation spectroscopy. A model is proposed to explain the observed increase in reactivity of the H-bonded ester. Hydrogen bonding (H-bonding) in both the monomeric and polymeric aspartate (ASP) esters was analyzed by 2D NMR spectroscopy. The difference in chemical shifts of the methylene protons before and after reaction was attributed to the geometrical effects of the five-membered ring formed from H-bonding. Monomeric aspartate esters (ASPE) were found to have the greatest difference in chemical shift, while the in-chain H-bonded protons of the PASPE were observed to have the least difference in chemical environments. Internal H-bonding in the ASPE affected its reaction with an aliphatic isocyanate (NCO) due to varying reactivities of the primary hydroxyl (OH) compared to the secondary amine (NH). Internal hydrogen bonding of the OH groups with the amine may also explain unexpected relative reactivities with isocyanates. Both NMR and FTIR spectroscopy indicated that the OH group was exclusively consumed with no NH reaction product detected. A lack of hydantoin ring formation upon further heating the NCO/ASPE reaction product proved that the OH group was more reactive. In an equimolar reaction of ASPE with cyclohexyl isocyanate, NMR and FTIR measurements showed quantitative formation of the urethane adduct instead of the expected urea.

Thermodynamic parameters of urethane formation reactions and concomitant processes

Thermodynamic parameters of reactions of methyl and phenyl isocyanates with a series of compounds were determined by quantum-chemical calculations. The products of these reactions model for various functional groups present in commercial polyurethanes. The thermodynamic stability series for compounds formed from aliphatic and aromatic isocyanates were constructed.

SWEDEN’S PERSTORP SPRINGS AHEAD

THE MANAGERS OF PERSTORP have been given a mission by the firm’s private equity owners: grow, and grow quickly, in a few chosen segments in the global specialty chemicals industry. And that is precisely what is happening. The Swedish company has embarked on a flurry of acquisitions to beef up a business portfolio that has polyol chemistry at its core. The firm’s latest deal, announced in mid-March, is also its biggest: intertwined agreements to take over Rhodia’s line of aliphatic isocyanates and LyondellBasell’s business in aromatic isocyanates. Aliphatic and aromatic isocyanates are reacted with polyols to produce industrial paint ingredients and flexible foams, respectively. The purchase includes plants in France and Texas and will add $460 million to Perstorp’s 2007 sales of about $1.27 billion. In February, Perstorp wrapped up its purchase of Solvay’s caprolactones business for nearly $310 million. The acquisition covered a plant in Warrington, England, a business with 2006 sales of about ...

Skin Exposure to Aliphatic Polyisocyanates in the Auto Body Repair and Refinishing Industry: II. A Quantitative Assessment

Skin exposure to isocyanates, in addition to respiratory exposures, may contribute to sensitization and asthma. Quantitative skin exposure data are scarce and quantitative methods limited. As part of the Survey of Painters and Repairers of Autobodies by Yale study, a method to sample and quantify human isocyanate skin exposure was developed (based on NIOSH 5525 method) and used to evaluate aliphatic isocyanate skin exposure in 81 auto body shop painters and body technicians. Wipe samples were collected from unprotected skin and from under PPE (gloves, clothing and respirator) using a polypropylene glycol-impregnated wipe. Hexamethylene diisocyanate (HDI), its polyisocyanates [HDI-derived polyisocyanates (pHDI)], isophorone diisocyanate (IPDI) and its polyisocyanates and IPDI-derived polyisocyanates (pIPDI) were quantified separately and also expressed as the total free isocyanate groups (total NCO). For unprotected skin areas, 49 samples were collected for spray painting, 13 for mixing, 27 for paint-related tasks (e.g. sanding and compounding) and 53 for non-paint-related tasks. Forty-three samples were also collected under PPE. The geometric mean (GM) [geometric standard deviation (GSD)] total NCO concentrations (ng NCO cm(-2)) for unprotected skin (hands, face and forearms) was 1.9 (10.9) and range 0.0-64.4. pHDI species were the major contributor to the total NCO content. Levels were very variable, with the highest concentrations measured for clear coating and paint mixing tasks. Isocyanate skin exposure was also commonly detected under PPE, with 92% of samples above the limit of detection. Levels were very variable with the overall GM (GSD) total NCO (ng NCO cm(-2)) under PPE 1.0 (5.2) and range (0.0-47.0) and similar under the different PPE (glove, respirator and clothing). The highest concentrations were detected for mixing and spraying tasks, 6.9 (5.3) and 1.0 (5.2), respectively. Levels under PPE were generally lower than unpaired samples obtained with no PPE, but not statistically significant. Total isocyanate GM load on exposed skin and under PPE was commonly 100-300 ng NCO per sample, except for higher levels on exposed forearms during spraying (GM 5.9 mug NCO). A quantitative method was developed for skin sampling of isocyanates. Using this method, the study demonstrates that skin exposure to aliphatic polyisocyanates during painting, mixing and paint-related tasks in auto body shop workers is common and also commonly detected under routine PPE.

Radiation induced effects in segmented poly(siloxaneurethaneureas) based on aliphatic and aromatic diisocyanates

Poly(siloxaneurethaneureas) (PSURURs) prepared from aromatic and aliphatic isocyanates were investigated upon exposure to ionising radiation. Radicals are formed both in siloxane and urethane segments. In comparison with aliphatic analogues it was found that in aromatic PSURURs: (1) concentration of all radicals is lower, (2) relative concentration of methylene radicals formed in siloxane units is higher, (3) the radiation yield of H 2 is more than three times smaller and (4) it seems that efficiency of cross-linking is less significant.

Skin Exposure to Aliphatic Polyisocyanates in the Auto Body Repair and Refinishing Industry: A Qualitative Assessment

Although respiratory exposures have been the primary concern with isocyanates, skin exposure also can occur and may contribute to sensitization and asthma. Methodologies to assess isocyanate skin exposure in the workplace are limited and skin exposure data scarce. The goals of this study were (i) to evaluate and validate the isocyanate colorimetric indicators against a quantitative assay, (ii) to evaluate the extent of isocyanate surface contamination and skin exposure among auto body shop workers and (iii) to evaluate isocyanate skin exposure determinants. The colorimetric indicators were compared with a high-performance liquid chromatography (HPLC) quantitative assay based on the National Institute for Occupational Safety and Health Method 5525 using paired laboratory sampling. The colorimetric indicators were then used to assess surface contamination and skin exposure to aliphatic isocyanates in 35 auto body shops and 124 workers as part of an epidemiologic study. The positive sample rate was calculated for various surfaces, body parts and tasks. The color intensity of the colorimetric indicators was rated on a scale 0 (yellow color) to 5 (deep red). Side-by-side comparisons of the qualitative method with the quantitative HPLC assay were also performed in the field using paired samples. Laboratory and field evaluation validated use of the colorimetric indicators. The rate of positive surface samples for isocyanates was 46% (n = 145/313). Thirty-four percent (73/216) of samples were positive for unprotected skin and 20% (n = 22/111) for skin under latex gloves. The highest positive rate observed on skin samples was obtained after paint mixing and spraying tasks. The colorimetric indicators were highly specific for isocyanates, but false negatives occurred when compared with the more sensitive HPLC quantitative assay. The presence of surface contamination and the performance of paint-related tasks were the major determinants of isocyanate skin exposure. This study documents extensive surface contamination and skin exposure, including under gloves, to aliphatic polyisocyanates during painting and paint mixing tasks in auto body shop workers. Contaminated surfaces and aerosol deposition during spray painting may both contribute to skin exposure. The colorimetric indicator is a quick, practical and low-cost, but not highly sensitive, industrial hygiene tool to detect isocyanate surface contamination and skin exposures following the use of isocyanate-containing products.

Slow Curing of Aliphatic Polyisocyanate Paints in Automotive Refinishing: A Potential Source for Skin Exposure

Two-component, polyurethane paints containing aliphatic isocyanates are widely used in autobody spray painting. Such isocyanates can cause asthma, and skin exposure may be an important route of sensitization and may contribute to the development of isocyanate asthma. Autobody workers are frequently in contact with recently painted, dried auto parts. It is not known how fast the newly painted car surfaces are fully cured, that is, for how long unbound, isocyanate species remain on painted surfaces after initial drying. To address this question, scrap sections of auto bodies were painted and dried by autobody shop painters following regular practice. Routinely used paints were sprayed 23 different times on the parts. Drying was accomplished by baking the part in a paint spray booth by heating it with a heat lamp or air drying in the shop. The 23 sprayed surfaces were sampled at regular time intervals after drying to determine the presence of free NCO groups using the semiquantitative SWYPE technique. Quantitative isocyanate analysis was also performed on two sprayed parts using NIOSH method 5525. Geometric mean curing time of 23 painted surfaces was 56.4 hr (range: 0.8 hrs to 32 days). Unbound isocyanate species of similar composition to the original bulk material remained present on the majority of sampled painted surfaces for up to 120 hours for typical paint formulations and for 1 month for others. The actual curing of polyurethane paints in autobody refinishing can be a slow process. Unbound isocyanates may remain on the surface of painted car parts for prolonged periods (days to weeks) after dried. Such surfaces are an under-recognized potential source of skin exposure to autobody workers.

Reaction of aromatic carboxylic acids with isocyanates using ionic liquids as novel and efficient media

Ionic liquids (ILs) based on 1,3-dialkylimidazolium and ammonium have been used as an efficient reaction media in the amidation of several carboxylic acids with isocyanates. The method has wide applicability, and the protocol is mild and efficient compared to the existing methods based on conventional solvents. Proper 'design' of the ILs allows us to obtain amides in good to excellent yields. In this reaction, both aromatic and aliphatic isocyanates could be used.

Organosilicon synthesis of isocyanates: II. Synthesis of aliphatic, carbocyclic, and fatty-aromatic isocyanates

Silylation of a series of aliphatic, carbocyclic, and fatty-aromatic amines gave the corresponding silyl derivatives whose yield depended on the electronic and steric structure of the substrate and the nature of the silylating agent. The yield of isocyanates obtained by phosgenation of the silyl derivatives under mild conditions decreased in going from aliphatic amines to benzylamines and rose as the length of the alkyl chain in fatty-aromatic amines extended. The most convenient procedure for the synthesis of low-boiling alkyl isocyanates was found to be based on the transformation of amines or ammonium salts into silyl or silyl silyl-carabamates, followed by pyrolysis of the latter in the presence of trichloro(phenyl)silane.

Kinetic study of polyurethanes formation by using differential scanning calorimetry

Kinetics of polyurethane formation between several polyols and isocyanates with dibutyltin dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by differential scanning calorimetry (DSC) using an improved method of interpretation. The molar enthalpy of urethane formation from secondary hydroxyl groups and aliphatic isocyanates is 72±3 kJ mol-1 and for aromatic isocyanates it is 55±2 kJ mol-1 . In the case of a single second order reaction for aliphatic isocyanates reaction, activation energy is 70±5 kJ mol-1 with oxypropylated polyols and 50±3 kJ mol-1 with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation energy is higher around 77 kJ mol-1 .