Reaction Of NCO Research Articles

Study of the Effect of PGDA Solvent on Film Formation and Curing Process of Two-Component Waterborne Polyurethane Coatings by FTIR Tracking

Waterborne polyurethane coatings were prepared using polyhydroxyacrylate dispersion, polyisocyanate, and propylene glycol diacetate (PGDA). The rate of reaction between hydroxyl and NCO groups in film formation and curing processes was studied by FTIR. The influence of PGDA amount on film formation and curing was also studied. Results showed that PGDA content had a significant effect on the curing process. With less than 10% PGDA, the role of PGDA was more to assist diffusion of polyhydroxyacrylate and polyisocyanate resin droplets. This promoted the reaction between hydroxyl groups and NCO. With more than 10% PGDA, its effect as a solvent was more and it inhibited the reaction between hydroxyl and NCO groups. When the amount of PGDA was about 10%, the synergy between both the roles promoted the crosslinking and curing reactions. The extent of the curing reaction of NCO was more than 70% in 4 h, which was significantly higher, compared with that of about 30% without PGDA. The good applicability and appearance of the waterborne polyurethane coating prepared in this study were verified for the application to carbon fiber metro vehicles.

STUDY ON MOISTURE-CUR ED POLYURETHANE AS UNDERCOATING LAYER FOR METALLIZATION

In this work a technique of metallizing substrate via electroless plating using moisture-cured polyurethane (MCPU) system as the undercoat is presented. MCPU prepolymer was prepared by mixing polyethylene glycol divinyl ether and diphenylmethane-4, 4’-diisocyanate in 1:1 ratio. The effects of etching time as well as curing period on the surface characteristic of MCPU undercoating were investigated. Contact angle measurements, FTIR and SEM were employed to study the changes on the surface of the treated MCPU undercoatsprior to electroless nickel plating. Electroless plating was performed using nickel bath and visual inspection was performed after completing the electroless plating cycles. Relative increase in wettability of the treated MCPU was observed. The surface became hydrophilic after subjecting to mild etching for 1 minute. SEM analysis revealed different pitted structures on the treated MCPU that were cured at different periods. FTIR analysis of the treated MCPU showed some chemical changes marked by the presence of free hydroxyl group and decrease of CH (methylene), urethane C=O, urethane amide and ether peaks. FTIR also showed the sign of further NCO reaction, which indicates by the decrease of NCO peak and increase of NH and urea C=O peaks. The standard pull-off testing method (ASTM D 4541) was employed to evaluate the adhesion strength of nickel deposits coated on MCPU undercoating layer.The test results revealed that curing period and etching time influence the adhesion performance.The results also show that at a selected curing period, prolong etching time will decrease the adhesion strength. Meanwhile prolong curing period will improve the adhesion strength.

Electron Captures on as a Trigger for Helium Shell Detonations

Abstract White dwarfs (WDs) that accrete helium at rates , such as those in close binaries with sdB stars, can accumulate large ( ) helium envelopes, which are likely to detonate. We perform binary stellar evolution calculations of sdB+WD binary systems with MESA, incorporating the important reaction chain (NCO), including a recent measurement for the rate. In large accreted helium shells, the NCO reaction chain leads to ignitions at the dense base of the freshly accreted envelope, in contrast to ignitions, which occur away from the base of the shell. In addition, at these accretion rates, the shells accumulate on a timescale comparable to their thermal time, leading to an enhanced sensitivity of the outcome on the accretion rate history. Hence, time dependent accretion rates from binary stellar evolution are necessary to determine the helium layer mass at ignition. We model the observed sdB+WD system CD and find that the inclusion of these effects predicts ignition of a helium shell, nearly a factor of two larger than previous predictions. A shell with this mass will ignite dynamically, a necessary condition for a helium shell detonation.

PU-Graphene Oxide Composite; Effect of Various Chain Extender on Properties.

High integration of electronic chip not only improved the electronic device’s efficiency, but also left the need to stop emitting heat. Thermal interface material (TIM) has been proposed to solve this problem. Traditionally, a large amount of high thermal conductive materials (such as Cu, Al or AlN) was added for better thermal conductivity, which caused undesirable weight-increasing and property-sacrificing. Graphene has great thermal conductivity and mechanical properties. Furthermore, owing to its low density, it is possible to make a lot of TIM even with a small amount. Being composited with PU, it can be an enhanced thermal conductive adhesive. Otherwise, amine compound is considered to be applicable as both a chain extender of PU and a reducing agent of Graphene oxide (GO). In this work, we synthesized PU-GO composite by chemical reaction of NCO and GO. We examined the effects of various amine compounds on chemical and physical properties of GO and PU-GO composite. Adhesion and thermal properties were also studied.

Mechanistic insight into selective catalytic combustion of acrylonitrile (C2H3CN): NCO formation and its further transformation towards N2.

A series of zeolite catalysts, M(Cu, Fe, Co)-ZSM-5, was prepared by an impregnation method and evaluated for the selective catalytic combustion of acrylonitrile (AN-SCC). Cu-ZSM-5, exhibiting the highest AN conversion activity and best N2 yield, was further selected for an AN-SCC mechanism investigation, wherein both experimental [in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)] and theoretical [density functional theory (DFT)] approaches were employed. The in situ DRIFTS revealed that AN-SCC followed a hydrolysis mechanism at T < 300 °C via intermediates of acylamino species (-CONH2) and NH3, while it followed an oxidation mechanism at T > 300 °C via an intermediate of NCO. The DFT simulations gave much deeper insights suggesting that: (i) the NCO could be generated by oxidation of AN over [Cu]+ active sites, with an assistance of dissociated atomic O from gaseous O2; (ii) three types of reaction routes could be proposed for the further reaction of NCO to produce N2, namely NCO direct dissociation, NCO coupling, and NO + NCO reaction; and (iii) the last route (NO + NCO), possessing the lowest energy barrier, was the most probable reaction pathway, wherein the NO could be produced by oxidation of NCO. The DFT energy calculation results and microkinetic analyses revealed that the NCO generation step, possessing an energy barrier of 17.0 kcal mol-1 and a forward reaction rate constant of 2.20 × 107 s-1, was the rate-determining step of the whole catalytic cycle.

A New Methodology for Assessing Macromolecular Click Reactions and Its Application to Amine--Tertiary Isocyanate Coupling for Polymer Ligation.

Click reactions have provided access to an array of remarkably complex polymer architectures. However, the term “click” is often applied inaccurately to polymer ligation reactions that fail to respect the criteria that typify a true “click” reaction. With the purpose of providing a universal way to benchmark polymer–polymer coupling efficiency at equimolarity and thus evaluate the fulfilment of click criteria, we report a simple one-pot methodology involving the homodicoupling of α-end-functionalized polymers using a small-molecule bifunctional linker. A combination of SEC analysis and chromatogram deconvolution enables straightforward quantification of the coupling efficiency. We subsequently employ this methodology to evaluate an overlooked candidate for the click reaction family: the addition of primary amines to α-tertiary isocyanates (α-tNCO). Using our bifunctional linker coupling strategy, we show that the amine–tNCO reaction fulfills the criteria for a polymer–polymer click reaction, achieving rapid, chemoselective, and quantitative coupling at room temperature without generating any byproducts. We demonstrate that amine–tNCO coupling is faster and more efficient than the more common amine–tertiary active ester coupling under equivalent conditions. Additionally, we show that the α-tNCO end group is unprecedentedly stable in aqueous media. Thus, we propose that the amine–tNCO ligation is a powerful new click reaction for efficient macromolecular coupling.

Factor defining the effects of glycine betaine on the thermodynamic stability and internal dynamics of horse cytochrome C.

A compatible osmolyte such as glycine betaine (GB) and low concentrations of a denaturant constrain the internal dynamics of natively folded carbonmonoxycytochrome c (NCO) at pH 7.0. GB and subdenaturing concentrations of guanidine hydrochloride (GdnHCl) or urea have a cumulative effect on the constrained dynamics of NCO. At higher denaturant concentrations, large-scale unfolding fluctuations dominate the dynamics and inclusion of GB opposes the structural fluctuations that cause unfolding of the protein. These deductions are made from kinetic and thermodynamic parameters measured for the CO dissociation reaction of NCO at varying concentrations of denaturant in the absence and presence of 1.0 M GB. Intermolecular docking between horse ferrocytochrome c and a denaturant or GB reveals that the denaturant-mediated constrained dynamics of the protein is due to polyfunctional interactions between the denaturant and different groups of protein while the GB-mediated restricted dynamics of the protein arises from both the direct interactions of GB with different side chains of Lys or Arg residues of the protein and indirect interactions of GB with the protein surface. Thermodynamic analysis of the thermal and GdnHCl-induced unfolding curves of ferrocytochrome c measured in the absence and presence of 1.0 M GB at pH 7.0 indicates that GB increases the thermodynamic stability of ferrocytochrome c at neutral pH. Analysis of thermal and urea-induced unfolding curves of ferricytochrome c measured at different GdnHCl concentrations in the absence and presence of 0.5-1.0 M GB at pH 7.0 and 3.8 suggests that GB counteracts the destabilizing effect of the denaturant at pH 7.0 but exhibits an additive effect on the destabilizing effect of the denaturant at pH 3.8.

Kinetics and mechanism of the water-assisted reaction of NCO with CH3OH: A quantum chemical study

The mechanism and kinetics of the hydrogen abstraction reaction between the NCO radical and CH3OH without and with one water molecule have been investigated theoretically. The potential energy surface profiles have been constructed at the CCSD(T)/6-311++G(2df,2pd)//BH&HLYP/6-311++G(2df,2pd)+ZPE×0.9335 level. The calculations show that the presence of one water molecule can noticeably reduce the energy barrier. However, the computed rate constants temperatures of 220–600K for the reaction with water is much smaller than that of the naked reaction. We would therefore expect that one water molecule could not play important roles on the NCO+CH3OH reaction in the atmosphere.

Theoretical Study on the Water-Assisted Reaction of NCO with HCHO

In this study, the reaction mechanism and kinetics of the hydrogen abstraction and addition reactions of NCO with HCHO in the absence and presence of water have been investigated theoretically for the first time. Our theoretical results indicate that direct hydrogen abstraction is favored in the formation of HNCO instead of HOCN and the addition pathways are negligible with and without water. The rate constants calculated at the CCSD(T)/aug-cc-pVTZ//BH&HLYP/6-311++G(3df,3pd) level with zero-point energy correction range from 1.60 × 10(-12) to 4.99 × 10(-12) cm(3) molecule(-1) s(-1) between 220 and 769 K without water and are in good agreement with the available experimental values. However, with the inclusion of water, the rate constants are slower by 2-8 orders of magnitude than those of the reaction without water. Accordingly, the effect of water on the reaction of NCO with HCHO is negligible in the atmosphere.

Isocyanate formation and reactivity on a Ba-based LNT catalyst studied by DRIFTS

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry (MS), coupled with the use of isotopically-labeled reactants (15N18O and 13CO), were employed to study the formation of isocyanate species during NOx reduction with CO, as well as isocyanate reactivity toward typical exhaust gas components. DRIFTS demonstrated that both Ba–NCO and Al–NCO were simultaneously formed during NOx reduction by CO under dry lean-rich cycling conditions. The Ba–NCO band was more intense than that of Al–NCO, and became comparatively stronger at high temperatures. During rich purging at 300 and 400°C, a near linear relationship was found between the increase in Ba–NCO band intensity and the decrease in Ba–NO3 band intensity, suggesting that Ba–NCO is directly derived from the reaction of Ba nitrate with CO. Both temperature-programmed surface reaction (TPSR) and isothermal reaction modes (ISR) were utilized to study the reactivity of isocyanate species under lean conditions. Simultaneous DRIFTS and mass spectrometric measurements during TPSR indicated that isocyanate reaction with H2O, O2, NO and NO/O2 took place almost immediately the temperature was raised above 100°C, and that all NCO species were removed below 300°C. The evolution of the NCO IR bands during ISR at 350°C demonstrated that the kinetics of NCO hydrolysis are fast, although a delay in N2 formation indicated that N2 is not the initial product of the reaction. In contrast, immediate N2 evolution was observed during NCO reaction with O2 and with NO+O2. Overall, it can be inferred that under dry cycling conditions with CO as the sole reductant, N2 is mainly generated via NCO reaction with NO/O2 after the switch to lean conditions, rather than being evolved during the rich phase. However, in the presence of water, isocyanate undergoes rapid hydrolysis in the rich phase, N2 generation proceeding via NH3.

Polyurethane-Modified Epoxy Monoacrylates Containing Two Different UV-Curable Groups: Preparation and Charaterization

Polyurethane-modified epoxy monoacrylates (PMEMA) containing two different UV- curable groups (double bond and epoxy groups) were synthesized. The changes of NCO groups during the synthesis process of PMEMA were measured by chemical titration method, and its Fourier Transform Infrared (FTIR) spectra were investigated. The results indicated that polyurethane chain segments can be grafted onto the epoxy monacrylates (EMA) by the reaction of NCO and OH groups. The FTIR of PMEMA showed that it contains both double bond of acrylic ester (UV radical curable) and epoxy groups (UV cationic curable).

Kinetics Studies of Synthesis of Double Bond of Blocked Water-Borne Polyurethane

With isophorone diisocyanate (IPDI) and polyether diols (N210) as raw, the water-borne polyurethane was synthesized. The end groups of the water-borne polyurethane were blocked with 2-hydroxyethyl acrylate (HEA). The chemical structures were characterized from Fourier Transform infrared spectroscopy (FTIR). The viscosity of the emulsion was investigated from rotary viscometer. The kinetics of reaction of NCO blocked with HEA was investigated, the results show that the reaction fits to a second-order reaction characteristic and the reaction rate is irrelevant with HEA.

Synthesis and Characterization of UV-Thermal Dual Hybrid Curable Organosilicon Modified Epoxy Monoacrylates

New UV-thermal dual hybrid curable organosilicon-modified epoxy monoacrylates (OMEMA) were synthesized in this study. The changes of NCO groups during the synthesis process of OMEMA were measured by chemical titration method, and its Fourier Transform Infrared (FTIR) spectra were investigated. The results indicate that organosilicon chain segments can be grafted onto the epoxy monacrylates (EMA) by the reaction of NCO and OH groups. The FTIR of OMEMA show that it contains both double bond of acrylic ester (UV curable) and epoxy groups (thermal curable).

In situ FTIR investigation of the role of surface isocyanates in the reduction of NOX by CO and C3H6 over model Pt/BaO/Al2O3 and Rh/BaO/Al2O3 NOX storage and reduction (NSR) catalysts

Monometallic Pt- and Rh-containing model NOX storage and reduction (NSR) catalysts were investigated by in situ FTIR spectroscopy in order to determine the type of species present on the surface under simulated lean exhaust conditions and to identify potential reaction intermediates during reduction by CO and propylene. The effect of precious metal selection, temperature, and water presence on the NOX storage and reduction chemistry was considered. The formation of surface isocyanate (NCO) species was observed during all cycling experiments, even in the presence of H2O, which prompted additional investigation on the role of these species in the NOX reduction mechanism. Stability and reactivity experiments with BaO/Al2O3, Pt/BaO/Al2O3 and Rh/BaO/Al2O3 confirmed that the reactions of NCO with NO and O2 – producing N2 – are metal catalyzed pathways, while the reaction of NCO with H2O – producing NH3 – is not. The contribution of NCO-related pathways to the overall N2 production mechanism could be significant, since quantification of the FTIR results suggests that up to 30% of the total N2 produced could be directly related to the reaction of surface isocyanates with O2.

The DFT study on mechanisms for NCO with C2 H5 reaction

A detailed investigation has been performed at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p) level for the reaction of NCO with C2H5 by constructing singlet and triplet potential energy surfaces (PES). The results show that the title reaction is more favorable on the singlet PES than on the triplet PES. On the singlet PES, the initial addition processes are barrierless and release lots of energy. The dominant channel occurs via the fragmentations of the initial adduct C2H5NCO and C2H5OCN to form C2H4 + HNCO and HOCN, respectively. With higher barrier heights, other products such as CH4 + HNC + CO, CH3CHNH + CO, CH3CH + HNCO, and CH3CN + H2 + CO are less competitive. On the triplet PES, the entrance reactions surpass significant barriers; therefore, it could be negligible at the normal atmospheric condition. However, the most feasible channel on the triplet PES is the direct hydrogen abstraction channel to form CH2CH2 + HNCO. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Theoretical study on the mechanism of the NCO + CH 3 reaction

The reaction of NCO with CH 3 is studied at B3LYP/6-11G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels. On the singlet potential energy surface (PES), the most feasible channel is direct radical–radical recombination leading to isomers OCNCH 3 and NCOCH 3. Further isomerization and dissociation of OCNCH 3 and NCOCH 3 to yield the dissociation products need to surmount the energy barrier at least 4.7 kcal/mol with respect to reactant, which indicate that these processes are kinetically unfeasible at normal temperatures and may become feasible only at high temperatures. Compared with the singlet pathways, the triplet pathways may have less contribution to the title reaction.

Direct ab initio dynamics calculations of the reaction rate for the hydrogen abstraction reaction of NCO with CH4 and C2H6

The kinetics of the hydrogen abstraction reactions NCO + CH4 (R1) and NCO + C2H6 (R2) have been studied over a wide temperature range. The minimum energy paths (MEPs) were calculated at the MP2/cc-pVDZ level and single-point calculations were refined at the G3MP2 level. The rate constants for the title reactions were calculated using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions. The fitted three-parameter formulae are k 1 = 2.52 × 10−22 T 3.46 exp(2466/T) and k 2 = 9.8 × 10−22 T 3.2 exp(411.8/T) cm3 molecule−1 s−1 for (R1) and (R2), respectively. The calculated rate constants were found to be in good agreement with the available experimental data. Deuterium kinetic isotope effects were also investigated. Both reactions show a significant kinetic isotope effect in the low-temperature range.

Kinetics of the H + NCO reaction

Ab initio transition state theory (TST) based master equation simulations are used to predict the temperature and pressure dependence of the H+NCO reaction rate and product branching. The barrierless entrance channels to form singlet HNCO and NCOH are studied with variable reaction coordinate TST employing a potential energy surface obtained from multi-reference configuration interaction ab initio calculations. The remaining channels, including reactions on the triplet surface, are studied with standard TST methods employing high level electronic structure results. The energy transfer parameters for the master equation simulations arise from a fit to the experimentally observed HNCO dissociation rate. The lowest energy threshold to formation of bimolecular products, 3NH+CO, lies well below the reactants. The bottleneck for intersystem crossing, which precedes the formation of 3NH+CO from the singlet adducts, becomes the dominant bottleneck for that channel at quite low energies relative to reactants. The effect of this bottleneck is studied with model calculations designed to reproduce detailed experimental observations of photolysis branching ratios. This bottleneck greatly reduces the flux from H+NCO to 3NH+CO via the singlet adducts. As a result, stabilization and reaction on solely the triplet surface are significant components of the overall rate. The present predictions for the high pressure and collisionless limit rate coefficients are accurately reproduced over the 200–2500K range by the expressions, 1.53×10−5T−1.86exp(−399/T)+1.07×103T−3.15exp(−15219/T) and 5.62×10−12T0.493exp(148/T)cm3molecule−1s−1, respectively, where T is in K. These predictions are in reasonably satisfactory agreement with the somewhat discordant experimental rate measurements.

Reduction of ferrate(VI) and oxidation of cyanate in a Fe(VI)–TiO 2–UV–NCO − system

The aqueous photocatalytic degradation of cyanate (NCO −), which is a long-lived neurotoxin formed during the remediation of cyanide in industrial waste streams, was studied in the ferrate(VI)–UV–TiO 2–NCO − system. Kinetics measurements of the photocatalytic reduction of ferrate(VI) were carried out as a function of [NCO −], [ferrate(VI)], [O 2], light intensity ( I o), and amount of TiO 2 in suspensions at pH 9.0. The photocatalytic reduction rate of ferrate(VI) in the studied system can be expressed as - d [ Fe ( VI ) ] / d t = kI o 0.5 [NCO −] [TiO 2]. The rate of photocatalytic oxidation of cyanate with ferrate(VI) was greater than the rate in the analogous system without ferrate(VI). The possibility of involvement of reactive ferrate(V) species for this enhancement was determined by studying the reactivity of ferrate(V) with NCO − in a homogeneous solution using a premix pulse radiolysis technique. The rate constant for the reaction of ferrate(V) and NCO − in alkaline medium was estimated to be (9.60 ± 0.07) × 10 2 M −1 s −1, which is much slower than the ferrate(VI) self-decomposition reaction ( k ≈ 10 7 M −1 s −1). An analysis of the kinetic data in the Fe(VI)–UV–TiO 2–NCO − system suggests that ferrate(V) is not directly participating in the oxidation of cyanate. Possible reactions in the system are presented to explain results of ferrate(VI) reduction and oxidation of cyanate.

Investigation of effects of dibutyltin dilaurate on reaction injection molding polyurethane-urea kinetics, morphology and mechanical properties by in situ FTIR

The bulk catalyst effect of dibutyltin dilaurate (DBTDL) on the reaction of NCO respectively with OH and NH2 was investigated in detail. The results showed that DBTDL had specific catalyst effect on the reaction of NCO with OH and no measurable effect on the reaction of NCO with NH2. In situ Fourier transform infrared spectroscopy (FTIR) used in the reaction injection molding (RIM) process showed that with increasing the concentration of DBTDL, the formation rate of the soft segment became fast, and the order degree of urea carbonyls became worse. Meanwhile, more arrange manners of urea carbonyl were present. The bands at 1653, 1647 and 1637 cm−1 were able to be detected at the low conversion. No hydrogen-bonded urea carbonyl available in the spectra at the beginning. The tensile-stress behavior showed that, with the increase of the DBTDL content, the interaction between polar groups became weak, while the virtual crosslinks also became weak. Although the break stress (d), 300‰δ and the hardness of elastomers decreased obviously, however, the tear strength, associated with the morphology of polyurethane-urea (PUU), showed the maximum when the DBTDL content was 2.63‰.