Hexamethylene-1,6-diisocyanate Research Articles

Nine years of patch testing with isocyanates in a clinic of occupational dermatology.

Isocyanates are used as starting materials of polyurethane (PU) products. They are relatively important occupational skin sensitizers. To analyse results of a large isocyanate patch test series of 19 isocyanate test substances and 4,4'-diaminodiphenylmethane (MDA), a marker of 4,4'-diphenylmethane diisocyanate (MDI) hypersensitivity. Test files were screened for positive reactions in the isocyanate series. Patients with positive reactions were analysed for occupation, exposure and diagnosis. In 2010-2019, 53 patients had positive reactions in the series (16% of 338 patients tested). MDA, the well-established screening substance for MDI allergy, was positive in 30 patients, an in-house monomeric MDI test substance in 23 patients and 3 different polymeric MDI test substances in 19-21 patients. We diagnosed 16 cases of occupational allergic contact dermatitis (OACD) from MDI including 3 pipe reliners. Hexamethylene-1,6-diisocyanate (HDI) oligomers in paint hardeners caused 5 cases of OACD, more cases than 2,4-toluene diisocyanate (TDI; n = 3) and isophorone diisocyanate (IPDI; n = 1) put together. In contrast to previous studies, polymeric MDI test substances were not superior to a monomeric MDI. Pipe reliners may get sensitised not only by epoxy products and acrylates but also by MDI in hardeners of PU pipe coatings. HDI oligomers were the second most important causes of OACD after MDI.

A novel method for the green synthesis of biobased hexamethylene-1,6-dicarbamate

The synthesis of polyurethane from renewable biomass is crucial for pursuing a sustainable future and a bio-based economy. The traditional production process of hexamethylene-1,6-diisocyanate (HDI) involves highly toxic phosgene, environmental...

Polymer Biocompositions and Nanobiocomposites Based on P3HB with Polyurethane and Montmorillonite.

Due to the growing interest in biopolymers, biosynthesizable and biodegradable polymers currently occupy a special place. Unfortunately, the properties of native biopolymers make them not good enough for use as substitutes for conventional polymers. Therefore, attempts are being made to modify their properties. In this work, in order to improve the properties of the poly(3-hydroxybutyrate) (P3HB) biopolymer, linear aliphatic polyurethane (PU) based on 1,4-butanediol (BD) and hexamethylene 1,6-diisocyanate (HDI) was used. The conducted studies on the effect of the amount of PU used (5, 10, 15 and 20 m/m%) showed an improvement in the thermal properties of the prepared polymer blends. As part of the tested mechanical properties of the new polymer blends, we noted the desired increase in the tensile strength, and the impact strength showed a decrease in hardness, in particular at the presence of 5 m/m% PU. Therefore, for further improvement, hybrid nanobiocomposites with 5 m/m% PU and organically modified montmorillonite (MMT) (Cloisite 30®B) were produced. The nanoadditive was used in a typical amount of 1-3 m/m%. It was found that the obtained nanobiocomposites containing the smallest amount of nanofillers, i.e., 1 m/m% Cloisite®30B, exhibited the best mechanical and thermal properties.

Novel synthesis of ultrafiltration membranes by crosslinking metal (II)-Alginate hydrogels with hexamethylene 1,6 -Diisocyanate in inert solvent: Application for remediation of wastewater by removal of toxic pollutants

Hexamethylene 1,6- diisocyanate (HDI) crosslinking agent has been used for novel synthesis of ultrafiltration (UF) membranes from polysaccharide derivatives as natural polymers for the first time. This process takes place by crosslinking the soft membranes of Cu (II)-alginate hydrogels (Cu-Alg2)n with 9 % of (HDI) in dryness acetone (DA) for obtaining its corresponding (CCu-Alg2)n as UF membranes. These new crosslinking membranes can be used for uptaking the toxic metal ion contaminants from wastewater in purification of drinking water. The pore size in such membranes can be controlled by varying the pH of the alginate sol using either NaH2PO4 or Na2HPO4 simple salts. The formed crosslinking membranes (CCu-Alg2)n were characterized by the elemental, FTIR and SEM/EDAX analyses. The experimental results of the crosslinking membranes (CCu-Alg2)n in its hydrogen form (CH2-Alg2)n showed high affinity for removal of some divalent metal ions such as Cu2+, Ni2+, Co2+, Cd2+ and Pb2+ ion pollutants at the pH s 2–6. Also, they revealed high selective separation of some tested metal ions such as Ag+ and Cu2+ from electrolyte mixtures involving these metal ions with other divalent metal ions (0.1–0.5 mmole /L) at 25 °C. Again, such crosslinking membranes of (CCu-Alg2)n has proven high capability for isolation the Serratia marcescens Grahams-negative fine bacterium from contaminated media. The nature of geometrical configuration for chelation of Cu (II) ions with the alginate functional groups (–COO– and –OH) in its non-crosslinked (Cu-Alg2)n and crosslinked with HDI membranes (CCu-Alg2)n were suggested and discussed.

Synthesis of Biuret Derivatives as Potential HIV‐1 Protease Inhibitors Using (LDHs‐g‐HMDI‐Citric Acid), as a Green Recyclable Catalyst

In this study, a novel catalyst based on layered double hydroxides (LDHs) attached by hexamethylene‐1,6‐diisocyanate (HMDI) and citric acid (LDHs‐g‐HMDI‐Citric acid) is reported and used to increase the yield of biurets synthesis. Biuret derivatives 5a–n were prepared by reaction of several phenyl allophanates (3a–d), which prepared from the reaction of phenyl chloroformate and urea derivatives (2a–d), with variously substituted amines (4a–g) in the presence of LDHs‐g‐HMDI‐Citric acid as a reusable heterogeneous catalyst at reflux condition for 60–180 min. These biurets (5a–n) were evaluated for human immunodeficiency virus type‐1 (HIV‐1) protease inhibitory activity by HIV‐1 p24 antigen ELISA kit and six of them (5n, 5i, 5j, 5 m, 5f, and 5a) showed moderate activity on HIV‐1 virus with IC50 values ranging from 55 to 100 μM compared with the azidothymidine as the reference drug (IC50 = 0.11 μM). Results of the in vitro test and docking study were in good correlation.

Synthesis of an oligomeric thickener for supercritical carbon dioxide and its properties

The applications of supercritical CO2 as a solvent are limited by its very low viscosity. A four-armed oligomeric CO2 thickener containing fluorine 1,6-bis(1,3-perfluorooctanoic acid biester-2-Urea)Hexane (BPFAUH) was synthesized with 2-amino-1,3-propanediol, (Boc)2D, pentadecafluorooctanoic acid, thionyl chloride, hexamethylene-1,6-diisocyanate (HMDI) as crude materials by using amino protection, esterification, deprotection, and nucleophilic addition reaction. and characterized using FTIR, 13C NMR and elemental analysis. TG analysis showed that the oligomeric thickener was thermally stable below 473.15 K. Its solubility in CO2 correlated well with the pressure. The viscosity of the system increased with increasing thickener concentration, but the viscosity of the thickener decreased with increasing temperature and shear rate. The system viscosity reached 19.2 mPa·s, a 480-fold increase compared to the initial viscosity, when 2.0 wt% thickener was added; this increase greatly exceeds that of other reported thickeners. The CO2-philic fluorocarbon groups promoted the solubility of the thickener; while intra-molecular thickener crosslinking occurred via O···H bonds. Thus, the molecule with four fluorocarbon groups and two urea groups formed a network structure to achieve superstrong CO2-thickening ability.

Novel separation process design for non-phosgene dimethylhexane-1,6-dicarbamate synthesis by reacting dimethyl carbonate with 1,6-hexanediamine

Abstract Hexamethylene-1,6-diisocyanate (HDI) is one of the most significant aliphatic diisocyanates for polyurethane production. The thermal decomposition of dimethylhexane-1,6-dicarbamate (HDC) has been considered as a very attractive non-phosgene route for HDI synthesis to realize industrialization because HDC can be synthesized by reacting 1,6-hexanediamine (HDA) with a green component, dimethyl carbonate (DMC). In this study, the optimal separation process design for non-phosgene HDC synthesis is investigated. Three design strategies to separate reaction products are proposed here. In the first two strategies, the low-boiling mixture containing un-reacted DMC and byproduct methanol is almost completely withdrawn from a column top, while some amount of un-reacted DMC is deliberately designed to be drawn out from the column bottom in the third strategy. Optimal processes designed by these three strategies are further enhanced by heat integration to reduce energy consumption. Simulation results reveal that the processes designed by strategy 3 need the least total annual cost and much economic benefit is achieved by the technologies of internal and external heat integrations. The key cost saving from internal heat integration is attributed to fully take advantage of the characteristic of DMC–methanol azeotrope at high pressure, and the higher column top temperature rendering condenser duty totally utilized by column bottom.

Fabrication and Characterization of Flexible Medical-Grade TPU Filament for Fused Deposition Modeling 3DP Technology.

The possibility of using additive manufacturing (AM) in the medicine area has created new opportunities in health care. This has contributed to a sharp increase in demand for 3D printers, their systems and materials that are adapted to strict medical requirements. We described herein a medical-grade thermoplastic polyurethane (S-TPU) which was developed and then formed into a filament for Fused Deposition Modeling (FDM) 3D printers during a melt-extrusion process. S-TPU consisting of aliphatic hexamethylene 1,6-diisocyanate (HDI), amorphous α,ω-dihydroxy(ethylene-butylene adipate) (PEBA) and 1,4 butandiol (BDO) as a chain extender, was synthesized without the use of a catalyst. The filament (F-TPU) properties were characterized by rheological, mechanical, physico-chemical and in vitro biological properties. The tests showed biocompatibility of the obtained filament as well as revealed no significant effect of the filament formation process on its properties. This study may contribute to expanding the range of medical-grade flexible filaments for standard low-budget FDM printers.

Non-phosgene synthesis of hexamethylene-1,6-diisocyanate from thermal decomposition of hexamethylene-1,6-dicarbamate over Zn–Co bimetallic supported ZSM-5 catalyst

Abstract A non-phosgene route for the synthesis of hexamethylene-1,6-diisocyanate (HDI) was developed via catalytic decomposition of hexamethylene-1,6-dicarbamate (HDC) over Zn–Co bi-metallic supported ZSM-5 catalyst. The catalyst was characterized by FTIR and XRD analyses. Three solvents dioctyl sebacate (DOS), dibutyl sebacate (DBS) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) were investigated and compared; DOS gave better performance. The catalytic performances for thermal decomposition of HDC to HDI using DOS as solvent were then investigated, and the results showed that, under the optimized reaction conditions, i.e.,10 wt% concentration of HDC in DOS, 250 °C temperature, 60 min reaction time, 83.8% yield of HDI had been achieved over Zn–Co/ZSM-5. Decomposition of the intermediate hexamethylene-1-carbamate-6-isocyanate (HMI) over Zn–Co/ZSM-5 in DOS solvent was further studied and the results indicated that yield of HDI from HMI reached to 69.6% (98.6% HDI selectively) at 270 °C, which further increased the yield of the total HDI (HDItol) to as high as 95.0%. Recycling of catalyst showed that HDI and HMI yield slightly decreased, and by-product yield increased after the catalyst was reused for 4 times. At last possible reaction mechanism was proposed.

An efficient green route for hexamethylene-1,6-diisocyanate synthesis by thermal decomposition of hexamethylene-1,6-dicarbamate over Co 3 O 4 /ZSM-5 catalyst: An indirect utilization of CO 2

Abstract The utilization of CO2 as raw material for chemical synthesis has the potential for substantial economic and green benefits. Thermal decomposition of hexamethylene-1,6-dicarbamate (HDC) is a promising approach for indirect utilization of CO2 to produce hexamethylene-1,6-diisocyanate (HDI). In this work, a green route was developed for the synthesis of HDI by thermal decomposition of HDC over Co3O4/ZSM-5 catalyst, using chlorobenzene as low boiling point solvent. Different metal oxide supported catalysts were prepared by incipient wetness impregnation (IWI), PEG-additive (PEG) and deposition precipitation with ammonia evaporation (DP) methods. Their catalytic performances for the thermal decomposition of HDC were tested. The catalyst screening results showed that Co3O4/ZSM-525 catalysts prepared by different methods showed different performances in the order of Co3O4/ZSM-525(PEG) > Co3O4/ZSM-525(IWI) > Co3O4/ZSM-525(DP). The physicochemical properties of Co3O4/ZSM-525 catalyst were characterized by XRD, FTIR, N2 adsorption-desorption measurements, NH3-TPD and XPS. The superior catalytic performance of Co3O4/ZSM-525(PEG) catalyst was attributed to its relative surface content of Co3 +, surface lattice oxygen content and total acidity. Under the optimized reaction conditions: 6.5% HDC concentration in chlorobenzene, 1 wt% Co3O4/ZSM-525(PEG) catalyst, 250 °C temperature, 2.5 h time, 800 ml·min− 1 nitrogen flow rate and 1.0 MPa pressure, the HDC conversion and HDI yield could reach 100% and 92.8% respectively. The Co3O4/ZSM-525(PEG) catalyst could be facilely separated from the reaction mixture, and reused without degradation in catalytic performance. Furthermore, a possible reaction mechanism was proposed based on the physicochemical properties of the Co3O4/ZSM-525 catalysts.

Zn-Co bimetallic supported ZSM-5 catalyst for phosgene-free synthesis of hexamethylene–1,6–diisocyanate by thermal decomposition of hexamethylene–1,6–dicarbamate

A set of mono- and bimetallic (Zn-Co) supported ZSM-5 catalysts was first prepared by PEG-additive method. The physicochemical properties of the catalysts were investigated by FTIR, XPS, XRD, N2 adsorption-desorption measurements, SEM, EDS and NH3-TPD techniques. The physicochemical properties showed that the ZnCo2O4 spinel oxide was formed on the ZSM-5 support and provided effectual synergetic effect between Zn and Co species for the bimetallic catalyst. Furthermore, bimetallic supported ZSM-5 catalyst exhibited weak, moderate and strong acidic sites, while the monometallic supported ZSM-5 catalyst showed only weak and moderate or strong acidic sites. Their catalytic performances for thermal decomposition of hexamethylene–1,6–dicarbamate (HDC) to hexamethylene–1,6–diisocyanate (HDI) were then studied. It was found that the bimetallic supported ZSM-5 catalysts, especially Zn-2Co/ZSM-5 catalyst showed excellent catalytic performance due to the good synergetic effect between Co and Zn species, which provided a suitable contribution of acidic sites. HDC conversion of 100% with HDI selectivity of 91.2% and by-products selectivity of 1.3% could be achieved within short reaction time of 2.5h over Zn-2Co/ZSM-5 catalyst.

Phosgene-free decomposition of dimethylhexane-1,6-dicarbamate over ZnO

In catalytic decomposition of dimethylhexane-1,6-dicarbamate (HDC) into hexamethylene-1,6-diisocyanate (HDI), Zn-containing homogeneous (i.e., zinc acetate) and heterogeneous (i.e., ZnO) catalysts were active among a number of catalysts tested, due to the great electron withdrawing ability of Zn ions. Particularly, when polyethylene glycol dimethyl ether was used as a solvent, ZnO was found to be relatively robust, because the catalytic performance was maintained up to the third use (HDC conversion of 93 % and HDI yield of 67 % at 180 °C for 1 h). Through investigation of a HDC/ZnO mixture at elevated temperatures by IR spectroscopy, a possible reaction scheme of ZnO-catalyzed decomposition of HDC was proposed. The H atom is removed from the N–H group of HDC by hydrogen bonding with an O site on the ZnO surface, followed by coordination of an O–C=O group in monodentate mode to a Zn site. The C–O group in the O–C=O linkage is then cleaved yielding the isocyanate and surface methoxide species. Finally, methanol is released from ZnO by a reaction between the surface methoxide and the hydroxyl species.

Phosgene-free synthesis of hexamethylene-1,6-diisocyanate by the catalytic decomposition of dimethylhexane-1,6-dicarbamate over zinc-incorporated berlinite (ZnAlPO4)

The phosgene-free synthesis of hexamethylene-1,6-diisocyanate (HDI) by the decomposition of dimethylhexane-1,6-dicarbamate (HDU) was carried out on a self-designed fixed-bed catalytic reactor, using zinc-incorporated berlinite (ZnAlPO4) as catalyst, dioctyl phthalate (DOP) as solvent and N2 as carrier gas. Factors influencing the yield of HDI, including the Zn/Al molar ratio, HDU concentration and liquid space velocity (LHSV), were investigated. Under the optimized reaction conditions, i.e., 4.8wt.% concentration of HDU in DOP, 100ml/min N2 flow rate, 0.09MPa vacuum, 623K reaction temperature, 1.2h−1 LHSV and catalyst usage 2.0g, a 89.4% yield of HDI had been achieved over the ZnAlPO4 (molar ratio Zn/Al=0.04) catalyst. The ZnAlPO4 catalyst was found to exhibit a considerable large on-stream stability and could be repeatedly used in the decomposition of HDU to HDI, after its regeneration.

The Preparation and Performance of Phenolic Foams Modified by Active Polypropylene Glycol

A series of active polypropylene glycols (APPGs) were synthesized by the reaction of hexamethylene-1,6-diisocyanate (HDI) and polypropylene glycol (PPG). They were then mixed and reacted with resol resin in catalyst condition to prepare the phenolic foams. The structure of modified phenolic foams was investigated. The influence of Mn of PPG and proportion of APPG on mechanical and fire-retardant performances of foams was discussed. The research results showed that the flexible PPG can be inducted into the crosslink structure of phenolic foam by the together crosslink reaction of –NCO groups in APPG with –CH2–OH groups in resol resin. When the molecular weight of PPG was 2000 and the dosage of APPG was 15% the max strain increased by 87%, mass loss (friability) decreased by 52%, thermal conductivity decrease from 0.033 to 0.028 W/(m·K), meanwhile the LOI can maintain above 30.

Contact allergy to aliphatic polyisocyanates based on hexamethylene‐1,6‐diisocyanate (HDI)

Aliphatic polyisocyanates based on hexamethylene 1,6-diisocyanate (HDI) are components of lacquers, coatings, and spray paints. They are mainly composed of HDI trimers, but also contain larger oligomers, and minute amounts of HDI monomers (<1%). HDI trimers occur as biuret, isocyanurate and asymmetrical types. We report on 4 patients with allergic contact dermatitis/contact allergy resulting from HDI-based polyisocyanates in polyurethane paints. The patients were examined at the Finnish Institute of Occupational Health in 2000-2009. The first two patients were diagnosed by testing with their own polyurethane hardeners and ingredients of the hardeners. In 2002, HDI isocyanurate (HDI-IC) trimer was added to our isocyanate series, and the last two patients were screened with the series. Patient no. 1 was exposed and sensitized to HDI biuret trimer, patient no. 2 to HDI-IC trimer, and patient no. 4 to HDI asymmetrical trimer. Patient no. 3 was positive with HDI-IC trimer. He had been handling several paint hardeners containing HDI-based polyisocyanates, but the subtypes of the trimers remained unidentified. All 4 patients were negative with HDI monomer. HDI trimers are novel contact allergens in workers who handle polyurethane paints. The allergic reactions cannot be explained by sensitization to HDI monomer.

SYNTHESIS AND PROPERTIES OF WATERBORNE POLYURETHANES MODIFIED BY EPOXY RESIN

A series of anionic waterborne polyurethane emulsion modified by epoxy resin were successfully prepared by the reaction of polycaprolactone diols(CAPA),isophorone isocyanate(IPDI),hexamethylene-1,6-diisocyanate(HDI) and epoxy resin(E-44) as crosslinker.Solidified films of the waterborne polyurethane were prepared by casting emulsions on Teflon surfaces.Fourier transform infared spectrometer(FTIR) and thermogravimetry analysis(TGA) were used to characterize the structure of the polyurethane.The mechanical properties and water contact angle of the cast films were also measured.The surface roughness and surface morphology of the films of waterborne polyurethanes were observed by atomic force microscopy(AFM).The particle size and distribution of the resultant polymer emulsions was tested by the dynamic laser light scattering(DLLS).FTIR indicates that epoxy group and hydroxyl group of E-44 both reacted with the polyurethane prepolymer.TGA indicates that the crosslink of E44 with polyurethane increased thermal stability of the modified polyurethanes.It was found that the tensile strength of films of modified polyurethane increased and the elongation at break decreased with increasing E-44 content,the water contact angle increases with increasing w(E-44),the smoothness of solidified films of waterborne polyurethane decrease when modified by E-44,resulting in water repellence functions.DLLS showed that the particle size of emulsion increased with increasing w(E-44).In order to obtain stable polyurethane emulsions and solidified films of waterborne polyurethanes with improved mechanical properties,the proper w(E-44) is 10%.

Determination of pulmonary irritant threshold concentrations of hexamethylene-1,6-diisocyanate (HDI) prepolymers by bronchoalveolar lavage in acute rat inhalation studies according to TRGS 430

Pulmonary irritant threshold concentrations of two hexamethylene-1,6-diisocyanate (HDI)-based prepolymers (I: polymeric emulsfier modified and II: oligomeric allophanate modified) were determined in acute inhalation studies according to TRGS 430 (Dangerous Substances Technical Rule, isocyanates, Germany), based on benchmark extrapolation of bronchoalveolar lavage fluid (BALF) total protein. It was also investigated if the method is robust enough to be transferred to an independent laboratory. Five male Wistar rats per group were exposed nose-only to the test substances as liquid aerosols to concentrations of 0, 0.5, 3, 15 mg/m 3 for both test substances with an additional test group at 50 mg/m 3 for test substance I. The duration of the exposure was 6 h, followed by serial sacrifices 1 day, 3 days and 7 days post exposure. BALF was analyzed for biochemical and cytological markers indicative for injury of the bronchoalveolar region. The exposure of rats to test substance I and II caused dose depended lung irritation with BALF total protein concentration being the most sensitive indicator of pulmonary effects. The extrapolated no observed adverse effect level of test substance I was 1.1 mg/m 3 and that of test substance II 2.3 mg/m 3. The acute pulmonary irritant threshold concentrations were found to be similar to those reported by [Pauluhn, J., 2004. Pulmonary irritant potency of polyisocyanate aerosols in rats: comparative assessment of irritant threshold concentrations by bronchoalveolar lavage. J. Appl. Toxicol. 24, 231–247] for HDI-homopolymers and other HDI-based polyisocyanates, and were at least 30 times higher than the MAK (occupational exposure limit) value for the HDI monomer (0.035 mg/m 3). Thus the EBW (exposure assessment value) for these two HDI-based prepolymers can be established at 10× MAK, i.e. at 0.35 mg/m 3.

Refractive index modulation in the polyurethane films containing diazo sulfonamide chromophores

The series of photochromic polyurethanes was obtained by modification of precursor polymers prepared from 4,4′-diphenylmethane diisocyanate (MDI), hexamethylene 1,6-diisocyanate (HDI) or toluene 2,4-diisocyanate (TDI) and N, N'-di-(2-hydroxyethyl) aniline. The precursor polymers were functionalized by an azo-coupling reaction to form the polymers with different degrees of functionalization and various heterocyclic sulfonamide groups. Ellipsometric measurements showed a decrease of the refractive index during illumination of thin polymer films with white light. The change of real part of the refractive index was in the range of 0.0033–0.0296 depending on the polymer kind and chromophore content. It was found that photocurrent was generated in the polymer films deposited onto indium tin oxide (ITO) glass plates. For the polyurethanes containing sulfathiazole groups in side chains the current density was up to 180 nA/cm 2. The formation of diffraction grating in the polymer films was easily achieved using linearly polarized laser light (532 nm) in a standard two beam coupling (TBC) system. The diffraction efficiency of the first diffraction beam was dependent on the chromophore content reaching ca. 12% for the derivatives of sulfamethoxazole.

Synthesis of polyurethane/polyethylene grafted polymers using cyclotriphosphazene as a coupling agent

The reaction between a dihydroxyphenoxycyclotriphosphazene containing allylic functions, 3, and hexamethylene-1,6-diisocyanate (HDI) leads to a new cyclotriphosphazene-substituted polyurethane 4. The structures of both classes of compounds involved in that synthesis were investigated by 31P-, 13C-, and 1H-NMR, infrared, and mass spectrometries, size-exclusion chromatography, and elemental analysis. The thermal behavior of 4 was investigated and compared to that of hexaphenoxycyclotriphosphazene, N3P3(OC6H5)6, and of a polyurethane synthesized from 1,3-bis(hydroxy)benzene and HDI. The free-radical-promoted grafting of 4 onto the polyethylene surface is described. The resultant surface was studied by ATR–IR, XPS, and contact-angle techniques. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1925–1934, 2003

Investigation of the competitive rate of derivatization of several secondary amines with phenylisocyanate (PHI), hexamethylene-1,6-diisocyanate (HDI), 4,4'-methylenebis(phenyl isocyanate) (MDI) and toluene diisocyanate (TDI) in liquid medium.

The stabilization of the isocyanate (NCO) groups during workplace sampling is necessary for their subsequent laboratory analysis. Most derivatization reagents are secondary amines. By carrying out a test in which two secondary amines are added to an isocyanate, the relative rates of these reactions can be evaluated. This evaluation is known for a monoisocyanate, phenylisocyanate (PHI), but is being developed for diisocyanates. This study deals with the relative reactivity (RR) of four diisocyanates: hexamethylene 1,6-diisocyanate (HDI), 4,4'-methylenebis(phenyl isocyanate) (MDI), and the ortho and para isomers of toluene diisocyanate (TDI) in addition to PHI, with four secondary amines: 1-(2-methoxyphenyl)piperazine (MOPIP), 9-(N-methylaminomethyl)anthracene (MAMA), 1-(9-anthracenylmethyl)piperazine (MAP), and dibutylamine (DBA). These competitive derivatization reactions are studied in three reaction solvents, namely acetonitrile, toluene, and acetonitrile doped with water (1% v/v). The results show that the order of reactivity, which doesn't change with the isocyanate as well as with the solvent used, is the following: DBA > MAP > MOPIP > MAMA. The relative difference in reactivity is a function of both the isocyanate and the solvent used. Hindered aromatic diisocyanates (TDI and MDI) show a greater difference in reactivity with the derivatization agents. These differences in reactivity are also modified by the solvent used. For example, larger differences are observed in acetonitrile than in toluene, but the introduction of water to acetonitrile, which does not affect the reaction yield, makes these differences smaller.