Improved preparation of chiral stationary phases via immobilization of polysaccharide derivative‐based selectors using diisocyanates

The classical method for the preparation of immobilized polysaccharide‐based chiral stationary phases (CSPs) with a diisocyanate was improved. Cellulose or amylose was directly coated onto 3‐aminopropyl silica gel after it was dissolved in a mixture of N,N‐dimethylacetamide, LiCl, and pyridine, then immobilized onto silica gel with a diisocyanate, and finally allowed to react with an excess of corresponding isocyanate. Four polysaccharide derivatives, 3,5‐dimethylphenylcarbamate and 3,5‐dichlorophenylcarbamate of cellulose, and 3,5‐dimethylphenylcarbamate and 5‐chloro‐2‐methylphenylcarbamate of amylose, were immobilized onto silica gel utilizing this method. Compared with the classical diisocyanate method, the improved procedure avoided the derivatization and regeneration of 6‐hydroxyl groups of cellulose and amylose, and thus showed an advantage for simple and economical preparation. The relationships among the amount of diisocyanate used, immobilization efficiency, and enantioseparation on the cellulose‐based CSPs were investigated. Also, the solvent durability of the obtained CSPs was examined with eluents containing chloroform or THF. By utilizing these eluents, the chiral recognition abilities of the obtained CSPs for some of the tested racemates were improved.     

Esca studies of polyurethanes: blood platelet activation in relation to surface composition

Segmented polyurethanes (SPU) were synthesized with polyethylene oxide (PEO), polypropylene oxide, or polytetramethylene oxide as the “soft segment,” from the respective polyether diols, of which molecular weight varied from 600 to 2000. The “hard segment” was created from ethylene diamine and tolylene diisocyanate or 4,4′-diphenylmethane diisocyanate. Platelet activation was assessed using columns packed with beads coated with each of the SPU by solutions from which the solvent was subsequently evaporated. Citrated whole human blood was passed through the columns and the platelet count in aliquots leaving the columns was compared with the platelet count in blood that had not contacted the column surface. By this method the fraction of platelets retained in the column averaged for several donors, ρ, was determined. In parallel experiments, SPU surfaces formed under identical conditions by evaporation of solvent were examined by X-ray electron spectroscopy for carbon, oxygen, and nitrogen content of the surface. The carbon C_1s spectra proved to be particularly useful, when analyzed for the components with peaks respectively at 286 eV (carbon not bonded to an ether oxygen) and at 288 eV (carbon bonded to an ether oxygen). The platelet retention index ρ was found to increase nearly linearly with the ratio of the 286-eV intensity to the 288-eV intensity, and extrapolated to nearly zero for zero value of the intensity ratio, which would correspond to amorphous PEO, suggesting that if a surface were only amorphous PEO it would be remarkably inactive toward platelets. In contrast, nitrogen spectra show no systematic relationship with ρ.     

Synthesis of polyurethanes from fluorinated diisocyanates

A number of polyurethanes based on fluorinated aliphatic diisocyanates, perfluorinated aromatic diisocyanates, and chlorinated aromatic diisocyanates have been prepared. The polyurethane prepared from perfluorotrimethylene diisocyanate and hexafluoropentanediol was a rubbery solid which hydrolyzed readily in air to a liquid or sticky solid but was stable if protected from moisture. The products of hydrolysis were isolated and identified. Polyurethanes based on hexafluoropentamethylene diisocyanate were synthesized by reaction of hexafluoropentanediamine with hexafluoropentamethylene bischloroformate and with tetrafluoro-p-phenylene bischloroformate. Polyurethanes were synthesized by reaction of tetrafluoro-p-phenylene diisocyanate with hexafluoropentanediol and pentanediol. Other perfluoroaryl diisocyanate-based polyurethanes were synthesized by reaction of tetrafluoro-m-phenylene diisocyanate with hexafluoropentanediol and with tetrafluoro-p-hydroquinone. Polyurethanes were also synthesized by reaction of tetrachloro-p-phenylene diisocyanate and 2,3,5,6-tetrachloro-p-xylylene-α,α′-diisocyanate with hexafluoropentanediol.     

Toughening polylactide by dynamic vulcanization with castor oil and different types of diisocyanates

Dynamic vulcanization of polylactide (PLA) with castor oil (CO) and three different diisocyanates, namely 4,4′-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), was performed to study the effect of diisocyanate type on the vulcanization process and on the morphology as well as mechanical properties of the PLA/CO-based polyurethane blends. The reactivity of the three diisocyanate followed the order of MDI > HDI > IPDI when reacting with castor oil. Interfacial compatibilization between PLA and the CO-based polyurethane occurred when the less reactive HDI and IPDI was used. Among all the blends, PLA/CO-IPDI showed the finest morphology and the best toughening efficiency. Incorporation of 20 wt% CO-IPDI increased the elongation at break and notched impact strength of PLA by 47.3 and 6.6 times, respectively. Cavitation induced matrix plastic deformation was observed as the toughening mechanism for the PLA blends with CO-based polyurethane. The effect of CO-IPDI content on the morphology and mechanical properties of PLA was studied in detail. The particle size of dispersed CO-IPDI and the elongation at break increased gradually, the tensile strength and Young's modulus decreased gradually, while the impact strength first increased and then decreased with increasing CO-IPDI content from 5 to 30 wt%. The maximum impact strength appeared for the blends with 20 wt% CO-IPDI.     

The Analysis of Toluene Diisocyanate and Diphenylmethane Diisocyanate by Gel Permeation Chromatography

Abstract

A gel permeation chromatographic method was developed for the quantitative analysis of toluene diisocyanate and diphenylmethane diisocyanate in polyurethane polymers. Standard curves were linear over the range of concentrations 2–35 μg/mL and a good correlation was established between the amount of diisocyanate injected and the peak height. In addition to rapid quantitation of diisocyanate monomers, the method developed also separates the polyurethane prepolymers and diisocyanate dimers and trimers, allowing analysis of components of commercial samples in a single step.     

Thermal degradation of linear polyurethanes and model biscarbamates

Thermal degradation of model biscarbamates, polyurethanes and poly(urethane-ureas) has been investigated by pyrolysis at atmospheric pressure. The biscarbamates were prepared from phenyl, benzyl, and cyclohexyl isocyanate and ethylene glycol. The polyurethanes and poly(urethane-ureas) were prepared from tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4′-dicyclohexylmethane diisocyanate (H₁₂-MDI) and poly(oxyethylene glycols) of various molecular weights. Rate constants for thermal degradation were obtained by measuring carbon dioxide evolution. The thermal degradation of all materials showed that the stability increased in the following manner: aromatic < aralkyl < cycloaliphatic. The separation and identification of the products of the thermal degradation gave an insight into the mechanisms involved in the pyrolysis of aromatic, aralkyl, and cycloaliphatic biscarbamates and the influence of temperature on these mechanisms.     

Nanostructured poly(urethane)s and poly(urethane-urea)s from reactive solutions of poly[styrene-b-butadiene-b-(methyl methacrylate)]-triblock copolymers

Poly[Styrene-b-Butadiene-b-(Methyl Methacrylate)], SBM triblock copolymers have been incorporated in different polyurethane, PU formulations in order to prepare nanostructured materials. Macrodiols used for PU synthesis were based on a central bis-phenol A, BPA unit with two hydroxyl-terminated oligo(oxypropylene), BPA-PO_x or oligo(oxyethylene), BPA-EO chains with varying lengths. The initial solubility of the three blocks and the rheological behavior of the solutions in macrodiols and also in two diisocyanates, isophorone diisocyanate, IPDI, and 1,3-xylylene diisocyanate, XDI have been first characterized. The PMMA block is the most soluble and its role during the reaction is to stabilize the initial nanostructure or to control the reaction-induced microphase separation.Block copolymers can be dissolved first in the macrodiol, or preferably in the diisocyanate. With BPA-PO_x and low SBM content (<10 wt%), transparent linear or crosslinked PU with well dispersed triblock nanoparticles have been prepared, depending on the molar mass of the macrodiol and on the concentration of diblock SB impurities present in the triblock. For high SBM concentrations (>50 wt%), a twin screw extruder had to be used for the blending. Under well-defined conditions, transparent linear PUs and linear segmented polyurethane-ureas have been prepared.This study confirms that for designing a nanostructured material from a reactive mixture with a triblock additive, one block, called “the nanostructuring block” has to remain soluble up to the end of the reaction.     

Studies on thermal, mechanical and morphological behaviour of caprolactam blocked methylenediphenyl diisocyanate toughened bismaleimide modified epoxy matrices

Diglycidyl ether of bisphenol A epoxy resin (DGEBA, LY 556) was toughened with 5%, 10% and 15% (by wt) of caprolactam blocked methylenediphenyl diisocyanate (CMDI) using 4,4′-diaminodiphenylmethane (DDM) as curing agent. The toughened epoxy resin was further modified with chemical modifier N,N′-bismaleimido-4,4′-diphenylmethane (BMI). Caprolactam blocked methylenediphenyl diisocyanate was synthesized by the reaction of caprolactam with methylenediphenyl diisocyanate in presence of carbon tetrachloride under nitrogen atmosphere. Thermal properties of the developed matrices were characterized by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), heat distortion temperature (HDT) and dynamic mechanical analysis (DMA). Mechanical properties like tensile strength, flexural strength and impact strength were tested as per ASTM standards. The glass transition temperature (T_g) and thermal stability were decreased with increase in the percentage incorporation of CMDI. The thermomechanical properties of caprolactam blocked methylenediphenyl diisocyanate toughened epoxy resin were increased by increasing the percentage incorporation of bismaleimide. The values of impact strength for epoxy resin were increased with increase in the percentage concentration of CMDI. The homogeneous morphology of CMDI toughened epoxy resin and bismaleimide modified CMDI toughened epoxy resin system were ascertained from scanning electron microscope (SEM).     

Thermal and dynamic mechanical analysis of cross-linked poly(esterurethanes)

New cross-linked poly(esterurethanes) (PEU) based on unsaturated olygo(alkyleneester)diol (OAE), 4,4’-diphenylmethane diisocyanate (MDI) and styrene or methyl methacrylate as curing monomers were prepared. The synthesis of PEU was performed in two steps. In the first step OAE was obtained from adipic acid, maleic anhydride and ethylene glycol. In the second step a prepolymer was obtained in a reaction of OAE with different amounts of 4,4’-diphenylmethane diisocyanate followed by crosslinking using previously mentioned curing monomers. The influence of structure of the poly(esterurethanes) on thermal and dynamic mechanical properties is studied. Thermogravimetric analysis shows that cross-linked poly(esterurethanes) demonstrate high thermal stability. Moreover the dynamic mechanical thermal analysis shows that the presence of styrene cross-linking chains in polymers lead to the phase separation in cross-linked poly(esterurethanes).     

Method for determining airborne diisocyanates

A method has been developed for quantitatively determining 3 typical diisocyanates, viz. 2,4-toluylene diisocyanate (2,4-TDI), hexamethylene diisocyanate (HDI) and 4,4-diphenyl-methane diisocyanate (MDI). The technique relies on chemisorption onto a suitable carrier material contained in an absorption tube coated with 1-(2-pyridyl)piperazine (2-PP). Stable urea derivatives with high molar absorptivity are formed, desorbed from the carrier material, separated by means of highpressure liquid chromatography and identified. The limits of detection for a sample volume of 20 1 of air are 0.9g m^–3 for 2,4-TDI and HDI, and 0.6g m^–3 for MDI. The derivatives are stable at 4°C for longer than 30 days. The influence of atmospheric humidity and the interference of dibutylamine on the detection reaction were investigated for 2,4-TDI and HDI. The whole procedure is easy to perform, highly sensitive and very reproducible and is suitable for monitoring concentrations of 2,4-TDI, HDI and MDI.Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

Hydrolysis of linear polyurethanes and model monocarbamates

Alkaline hydrolysis of model carbamates, polyurethanes, and poly(urethane-ureas) has been investigated. The model carbamates were based upon phenyl, benzyl, and cyclohexyl isocyanates. The polyurethanes and poly(urethane-ureas) were prepared from tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) and a poly(oxyethylene)glycol of 6000 molecular weight. Pseudo-first-order rate constants of hydrolysis were obtained in aqueous pyridine solution at 110°C, and second-order rate constants were obtained in aqueous KOH solution for the model biscarbamates. Pseudo-first-order rate constants of hydrolysis were obtained in alcoholic KOH solution for the polyurethanes and poly(urethane-ureas). The hydrolysis of the model carbamates showed that the stability increased in the following manner: phenyl < benzyl < cyclohexyl. The pseudo-first-order rate constants were dependent upon the pK_b of the corresponding amines. The hydrolysis of the polyurethanes and poly(urethane-ureas) showed that the stability increased in the following manner: aromatic < aralkyl < cycloaliphatic. It was shown that polyurethanes are more susceptible to alkaline hydrolysis than to acidic hydrolysis.     

UV-curable low-surface-energy fluorinated poly(urethane-acrylate)s for biomedical applications

Novel UV-curable fluorinated poly(urethane-acrylate) (FPUA) oligomers have been synthesized from 1H,1H,12H,12H-perfluoro-1,12-dodecanediol (PFDDOL), either 1,6-hexamethylene diisocyanate (HDI) or 4,4′-diphenylmethane diisocyanate (MDI), and 2-hydroxyethyl methacrylate (HEMA) for end-capping with photo-crosslinkable methacrylate groups. The fluorine content and the nature of the isocyanate were investigated to determine their effects on the physical properties, surface properties, and blood compatibilities of the polymers. The introduction of hydrophobic fluorocarbon chains led to phase separation and a low total surface energy, which reduced the adhesion of blood platelets onto the materials. The HDI-type UV-curable, fluorinated poly(urethane-acrylate) exhibited a low-surface-energy and superior blood compatibility (as determined from RIPA values).     

Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols. II. Synthesis and characterization of segmented polyurethanes from HDI and MDI

Various new thermoplastic segmented polyurethanes were synthesized by a one-step melt polymerization from aliphatic-aromatic α,ω-diols containing sulfur in the aliphatic chain, including 4,4′-(ethane-1,2-diyl)bis(benzenethioethanol), 4,4′-(ethane-1,2-diyl)bis(benzenethiopropanol) and 4,4′-(ethane-1,2-diyl)bis(benzenethiodecanol) as chain extenders, hexane-1,6-diyl diisocyanate (HDI) or 4,4′-diphenylmethane diisocyanate (MDI) and 20-80 mol% poly(oxytetramethylene)diol (PTMO) with molecular weight of 1000 g/mol as a soft segment. The reaction was conducted at the molar ratio of NCO/OH = 1 and 1.05, and in the case of the HDI-based polyurethanes in the presence of dibutyltin dilaurate as a catalyst. The effect of the diisocyanate used on the structure and some physicochemical, thermal and mechanical properties of the segmented polyurethanes were studied. The structures of these polyurethanes were examined by FTIR and X-ray diffraction analysis. The thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. Shore hardness and tensile properties were also determined. All the synthesized polymers showed partially crystalline structures. The MDI-based polyurethanes were products with lower crystallinity, higher glass-transition temperature (T_g) and better thermal stability in comparison with the HDI-based ones. The MDI series polymers also exhibited higher tensile strength (up to ∼36 MPa vs. ∼23 MPa) and elongation at break (up to ∼3900% vs. ∼900%), but lower hardness than the analogous HDI series polyurethanes. In both series of the polymers an increase in PTMO soft-segment content was associated with decreased crystallinity, T_g, hardness and tensile strength. An increase in PTMO content also involved an increase in elongation at break.     

Diisocyanate route as a convenient method for the preparation of novel optically active poly(amide-imide)s based on N-trimellitylimido-S-valine

A new class of optically active poly(amide-imide)s based on an α-amino acid was synthesized via direct polycondensation reaction of different diisocyanates with a chiral diacid monomer. The step-growth polymerization reactions of N-trimellitylimido-S-valine (TISV) (1) with 4,4′-methylene-bis(4-phenylisocyanate) (MDI) (2) was performed under microwave irradiation, as well as solution polymerization under graduate heating and reflux conditions. The optimized polymerization conditions for each method were performed with tolylene-2,4-diisocyanate (TDI) (3), hexamethylene diisocyanate (HDI) (4), and isophorone diisocyanate (IPDI) (5) to produce optically active poly(amide-imide)s via diisocyanate route. The resulting polymers have inherent viscosities in the range of 0.02-1.10 dL/g. Decomposition temperatures for 5% weight loss (T₅) occurred above 300 °C (by TGA) in nitrogen atmospheres. These polymers are optically active, thermally stable and soluble in amide-type solvents. Some structural characterization and physical properties of this new optically active poly(amide-imide)s are reported.     

Effect of the diisocyanate on the structure and properties of polyurethane acrylate prepolymers

In this study, we investigated the role of diisocyanate on the properties of polyurethane acrylate (PUA) prepolymers based on polypropylene oxide (M̄_n = 2000 g · mol⁻¹). The diisocyanates studied were isophorone diisocyanate, 4‐4′dicyclohexylmethane diisocyanate, and toluene diisocyanate (pure 2,4‐TDI, pure 2,6‐TDI, and a TDI mixture, TDI_tech). The molecular structure of the diisocyanate had a major role on the course of the polycondensation and, more precisely, on the sequence length distribution of the final prepolymer. Moreover, the structural organization of the prepolymer also strongly depended on the nature of the diisocyanate. Two types of behaviors were particularly emphasized. On the one hand, the PUA synthesized from 2,4‐TDI displayed an enhanced intermixing between soft polyether segments and hard urethane groups, as revealed by the analysis of hydrogen bonding in Fourier transform infrared. Consecutively, the glass transition shifted to higher temperatures for these polymers. On the other hand, strong hard–hard inter‐urethane associations were observed in 2,6‐TDI‐based prepolymers; these led to microphase segregation between polyether chains and urethane groups, as revealed by optical microscopy. This inhomogeneous structure was thought to be responsible for the unusual rheological behavior of these PUA prepolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2750–2768, 2000     

UV-curable poly(ethylene glycol)–based polyurethane acrylate hydrogel

Poly(ethylene glycol) (PEG) with molecular weight (M_n) of 1000, 2000, 3000, and 4000 g/mol, four types of diisocyanate [hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), isophorone diisocyanate (IPDI), and toluene diisocyanate (TDI)], two types of comonomers [acrylamide (AAm) and acrylic acid (AAc)] that comprised up to 60% of the total solid were used to prepare UV-curable PEG–based polyurethane (PU) acrylate hydrogel. The gels were evaluated in terms of mechanical properties, water content as a function of immersion time and pH, and X-ray diffraction profiles of dry and swollen films. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2703–2709, 1999     

Synthesis and characterization of poly(urethane-sulfone)s

Eight poly(urethane-sulfone)s were synthesized from two sulfone-containing diols, 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333) and 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343), and three diisocyanates, 1,6-hexamethylene diisocyanate (HMDI), 4,4′-diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI, 2,4- 80%; 2,6-20%). As a comparison, eight polyurethanes were also synthesized from two alkanediols, 1,9-nonanediol and 1,10-decanediol, and three diisocyanates. Diol-333 and Diol-343 were prepared by the addition of 1,3-propanedithiol or 1,4-butanedithiol to allyl alcohol and subsequent oxidation of the resulting sulfide-containing diols. The homopoly(urethanesulfone)s from HMDI and MDI are semicrystalline, and are soluble in m-cresol and hot DMF, DMAC, and DMSO. The copoly(urethane-sulfone)s from a 1/1 molar ratio mixture of Diol-333 and Diol-343 with HMDI or MDI have lower crystallinity and better solubility than the corresponding homopoly(urethane-sulfone)s. The poly(urethane-sulfone)s from TDI are amorphous, and are readily soluble in m-cresol, DMF, DMAC, and DMSO at room temperature. Differential scanning calorimetry data showed that poly(urethane-sulfone)s have higher glass transition temperatures and melting points than the corresponding polyurethanes without sulfone groups. The rise in glass transition temperature is 20–25°C while the rise in melting temperature is 46–71°C. © 1994 John Wiley & Sons, Inc.     

Preparation and properties of aromatic copolyamides from aromatic diisocyanates and aromatic dicarboxylic acids

Wholly aromatic random copolyamides of high molecular weights were prepared by the high-temperature solution polycondensation of an aromatic diisocyanate, 4,4′-methylenedi(phenyl isocyanate) or 2,4-tolylene diisocyanate, with a mixture of isophthalic acid and 4,4′-oxydibenzoic acid. Glass transition temperatures of the polyamides and copolyamides were between 229 and 273°C; this depended on the combination of diisocyanates and dicarboxylic acids used. These aromatic copolyamides showed better solubility in various organic solvents and reduced crystallinity, compared to the corresponding homopolyamides. The copolyamides prepared from 2,4-tolylene diisocyanate had greater solubility and higher glass transition temperatures than those obtained from 4,4′-methylenedi(phenyl isocyanate).     

Determination of airborne isocyanates as di-n-butylamine derivatives using liquid chromatography and tandem mass spectrometry

A method for the determination of isocyanates as di-n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d₉-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1 μg ml⁻¹ of the studied derivatives was <2%. Performing MRM of the product ion [DBA + H]⁺ (m/z = 130) from the protonated molecular ion resulted in the lowest detection limits, down to 10 amol (for TDI). Quantification of concentrations below 10⁻⁶ of the occupational exposure limit (OEL) for TDI during 10 min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M + Li]⁺ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d₄-HDI, d₃-2,4-TDI, d₃-2,6-TDI and d₂-MDI), (2) d₉-DBA derivatives of the corresponding isocyanates and (3) d₁₈-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series.     

A highly sensitive high-performance liquid chromatographic procedure for the determination of isocyanates in air

Summary A sensitive high-performance liquid chromatographic procedure is described to analyse hexamethylene diisocyanate (HDI), 2,4- and 2,6-toluene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI) in air. The isocyanates are trapped on a sorbent coated with 1-(2-methoxyphenyl)piperazine (MPP). The resulting derivatives are separated using a column switching technique using either a diode array UV detector or an electrochemical detector. Working ranges are 1–5000 and 0.05–400 pmol for UV and EC detection, respectively. Virtually no breakthrough occurs if an air volume of up to 1500 l is sampled, and relative detection limits between 0.1 and 1 ng/m³ can be achieved. The procedure can be used to determine HDI and MDI in work place atmospheres and indoor air.Dedicated to Prof Dr. E. Lahmann on the occasion of this 65th birthday