Real-time FTIR Spectroscopy Research Articles

Synthesis and photopolymerization of norbornyl epoxidized linseed oil

Norbornyl epoxidized linseed oil was synthesized via Diels–Alder reaction of cyclopentadiene with linseed oil at high pressure (∼200 psi) and high temperature (240 °C), followed by an epoxidation using hydrogen peroxide with a quaternary ammonium tetrakis(diperoxotungsto) phosphate(3−) epoxidation catalyst. The products were characterized using 1H and 13C NMR, FT-IR, and electrospray ionization mass spectroscopy. Photo-induced curing kinetics of norbornyl epoxidized linseed oil coatings was investigated using real-time FT-IR spectroscopy with a fiber optic UV-curing system. The norbornyl epoxidized linseed oil was formulated with three different divinyl ether reactive diluent. The effect of divinyl ether concentration and types of divinyl ether on the curing reaction was investigated. It was found that the curing rate of norbornyl epoxidized linseed oil was lower than that of cycloaliphatic epoxide, but higher than epoxidized linseed oil. The incorporation of divinyl ethers increased the curing rate and overall conversion of the epoxide groups. Of the three divinyl ethers used, coating with triethyleneglycol divinyl ether showed the highest curing rate and coating with cyclohexane dimethanol divinyl ether showed the lowest curing rate.

INFLUENCE OF WOOD EXTRACTS ON THE UV CURING OF ACRYLATE COATINGS

ABSTRACT The effect of wood extracts on the kinetics of UV curing of an urethane diacrylate was studied by real-time FTIR spectroscopy. Whereas extracts from rose wood (Dalbergia latifolia) inhibit the reaction, curing is not significantly affected by extracts from teak wood (Tectona grandis). Data of the pendulum hardness of the coatings confirm these results. Moreover, the radical scavenging capacity of the extracts was determined relative to benzoquinone by a radiation-chemical method.

UV curing of a pressure sensitive adhesive coating studied by real-time FTIR spectroscopy and laboratory scale curing experiments

Real-time FTIR spectroscopy was used to study the UV-light induced crosslinking of a pressure sensitive adhesive based on a saturated acrylic polymer bearing a photoreactive functional group in the side chain. To simulate production parameters, e.g., cure speed and number of required UV lamps, single or multiple UV-light flash experiments were performed which have shown that the amount of crosslinked polymer chains in the adhesive depends on the applied UV dose. The same result was observed by varying the intensity of the UV-light. The properties of the pressure sensitive adhesive, e.g., peel and shear strength, were determined by UV curing using a laboratory irradiation unit. These results were compared with those of the RTIR spectroscopy experiments.

Optimization of radical photopolymerization in hybrid sol-gel glasses: advantages of bicomponent photoactive systems

AbstractUse of organosilanes as hybrid systems is of increasing importance for their promising applications in the optical field. Considerable attention has been paid to the study of the inorganic network. However, poor information concerning the organic part involved in the solgel process is available. This is yet a fundamental requirement for optical applications where homogeneity at molecular scale is essential. Taking into account the specificity of the sol-gel medium, characteristics of the organic part have to be adapted with the view of optimizing the properties of the final material. Hybrid material used in this study consisted of organosilane precursor with methacrylate functions, titanium isoproxide, methacrylic acid and photoinitiator. The polycondensation of the inorganic component was achieved sequentially and simultaneously with the photopolymerization of the organic one to provide a mutually interpenetrating network. Polymerization in the UV range presents the advantages of fast-curing at temperature compatible with fragile substrates and spatio-temporal selectivity of the reaction. Characteristics of the photopolymerization process taking place in hybrid sol-gel materials were investigated by UV and Real Time FTIR spectroscopy. Besides the study of the organic network, NMR investigations led information relative to the inorganic network formation during the sol maturation. The whole results provide insights into the optimization of the photochemical step. Indeed, it was demonstrated that titanium components added as passive components to increase the refractive index of the layer, can induce polymerization under a medium pressure mercury arc lamp irradiation. In addition, mix photoactive systems involving an organic photoinitiator and titanium components were investigated and led to a better efficiency for the photoinitiation. Final materials with higher conversion ratio of the methacrylate function and requiring shorter irradiation times were achieved.

Effect of Colloidal Fillers on the Cross-Linking of a UV-Curable Polymer: Gel Point Rheology and the Winter−Chambon Criterion

The effect of colloidal silica fillers on the cross-linking behavior of a model UV-curable polymer system (thiol−ene) is studied using in situ rheology and real-time FTIR spectroscopy. The validity of the Winter−Chambon criterion (convergence of the loss tangents at the gel point) is examined for the cross-linking of these filled polymers, some of which are strongly flocculated dispersions (physical gels) prior to chemical cross-linking. Two different types of colloidal silica particles are studied: one with octyl chains tethered to the surface and the other with methyl surface groups. The Winter−Chambon criterion is satisfied for all samples containing the methyl-terminated silica. However, the criterion breaks down for samples containing the octyl-modified silica, with the loss tangents not converging at any single point. This suggests the absence of a self-similar critical gel at the gel point in the latter case. Neither type of silica particles alters the mechanism of the cross-linking reaction, as revealed by FTIR spectroscopy, but they do retard the cross-linking kinetics. An alternate method is suggested for determining the chemical gel point of filled systems that fail to obey the Winter−Chambon criterion. This method involves monitoring the critical strain (limit of the linear viscoelastic region) at various UV exposure times. A dramatic increase is observed in the critical strain at the gel point, indicating a transition from weak, physical bonds to strong, covalent cross-links.

Investigation of dipole orientation in a side-chain second-order nonlinear optical poly(urethane-imide) by real-time variable temperature FT-IR spectroscopy

The orientation and relaxation of the second-order nonlinear optical (NLO) groups in a side-chain poly(urethane-imide) before and after the electric poling has been investigated with real-time variable temperature FT-IR spectroscopy by monitoring the symmetrical stretching vibration of the nitro group. In situ second harmonic generation (SHG) and ultraviolet-visible (UV–Vis) spectroscopy were also used to compare with the FT-IR results. The results obtained by these techniques are in good agreement with each other.

Preparation of a Novel Infrared Photoinitiator and Kinetic Monitoring of Photopolymerization by Real Time FT-IR Spectroscopy

In this paper, a novel cationic cyanine dye-borate complex, 1,3,3,1′,3′,3′-hexamethyl-11-chloro- 10,12 propylenetricarbocyanine triphenylbutylborate was prepared and used as the photoinitiator in infrared laser-induced photopolymerization of acrylates. It had a maximum electron absorption at 786 nm, which matched well with the output wavelength of the adopted infrared laser diode, with a maximum molar extinction coefficient of 1.4×105 L mol−1 cm−1 in chloroform solution. Under the irradiation of infrared laser the polymeric samples based on phthalicdiglycol diacrylate (PDDA), binder, photoinitiator and solvent polymerized and the polymerizing process was monitored through Real Time FT-IR spectroscopy (RTFT-IR). The double bond conversion was determined from the reduction of the absorption of acrylate monomer at 1635 cm−1 and 1620 cm−1 (CH2=CH strentching) in FT-IR spectra during laser irradiation. As the concentration of photoinitiator rose, the polymerization rate (Rp) increased rapidly but then decreased when the concentration reached a critical value. Rp and the ultimate double bond conversion of sample increased when the infrared laser power was enhanced, whereas they fell greatly as the thickness of the polymeric sample layer increased.

New insights into photoinduced processes in hybrid sol–gel glasses containing modified titanium alkoxides

Hybrid organic–inorganic sol–gel compounds have been widely used for the design of new optical devices, since they combine the characteristics of both glasses and polymers and improve the properties of the final material. Hybrid precursors in which both phases are chemically grafted are of increasing interest: volume shrinkage is minimized and phase separation can be kept below the level of Rayleigh scattering, thus leading to highly transparent glasses. Polymerizable acrylate or methacrylate functions grafted onto modified silicone alkoxides can react ia a free-radical mechanism initiated either by heating or UV-light. Considerable attention has already been focused on the chemical mechanisms involved in the construction of the inorganic network. However, no extensive study of the organic part of the process has so far been conducted. This paper points out the characteristics of the photopolymerization process taking place in hybrid sol–gel materials. In particular, the influence of inorganic moieties on the photopolymerization kinetics was studied by UV and real time FTIR spectroscopy. Particular interest was focused on the incorporation of alkoxymetals that are usually added to improve the optical and physical properties of the final material. The role of the titanium component in the photopolymerization process is emphasized. The results provide insights into processes leading to simultaneous formation of interpenetrating organic–inorganic networks and are of crucial importance for the generation of optical devices.

UV curing of aqueous polyurethane acrylate dispersions. A comparative study by real-time FTIR spectroscopy and pilot scale curing

Real-time FTIR spectroscopy was used to study the chemical and physical factors, e.g., photoinitiator and temperature, affecting the UV curing of dried films from aqueous polyurethane acrylate dispersions. Poor conversion of the acrylate double bonds (67%) observed at room temperature can be overcome by irradiation at elevated temperatures. At 353 K almost complete conversion is observed, even with reduced photoinitiator content. Single or multiple UV-light flash experiments were performed to simulate technical parameters, e.g., cure speed and number of required UV lamps, with the help of RTIR spectroscopy. The results obtained were confirmed by pilot-scale UV curing experiments: one or, at most, two UV lamps of high intensity are sufficient for the curing process with respect to the double-bond conversion. The coatings based on the polyurethane acrylate dispersion show low sensitivity towards oxygen from air. Moreover, in comparison to UV curing under inert nitrogen atmosphere, a small “positive” effect on the conversion in the presence of air has been observed, which might be due to the contribution of peroxyl radicals or their decomposition products to curing.

The effect of temperature on the kinetics of diacrylate photopolymerizations studied by Real-time FTIR spectroscopy

Real-time FTIR spectroscopy was used to study the effect of temperature on the kinetics of photopolymerization from room temperature up to 160°C. A highly viscous epoxy diacrylate and tripropylene glycol diacrylate (TPGDA) as systems of lower viscosity were used to study the influence of viscosity on the polymerization rate, the induction period, and the ultimate conversion. Different behaviour was observed at temperatures below and above ca. 90°C. In the epoxy diacrylate, the polymerization rate first distinctly increases with temperature due to the drop of viscosity, whereas in TPGDA the polymerization rate only little increases or is even independent of temperature depending on the photoinitiator used. The induction period decreases due to the decreasing solubility of oxygen in the reactive formulation. At higher temperatures, termination processes lead to a decrease of the polymerization rate if morpholino ketones are used for initiation. Simultaneously, the induction period re-increases. In contrast, systems initiated by a hydroxy alkylphenone or benzildimethyl ketal continue the trends from below 90°C.

Novel cross-linkable hole-transport monomer for use in organic light emitting diodes

Thin films of a cross-linkable hole-conducting monomeric triarylamine were investigated. The rate of photocross-linking and the overall polymerization yield were measured using real-time FT-IR spectroscopy. The electrical properties were characterized in a typical diode configuration using indium tin oxide and aluminum as the contacts. The current passed through the devices was found to be limited by the injection of holes into the semi-conducting polymer layer by tunneling. Cross-linked layers withstood about 20 times higher currents than non-cross-linked layers before dielectric breakdown occurred.

Studying Polymer-Dispersed Liquid-Crystal Formation by FTIR Spectroscopy. 1. Monitoring Curing Reactions

UV-induced matrix cross-linking is the method of choice to form polymer-dispersed liquid crystals (PDLCs). In this paper, real-time FTIR spectroscopy is applied to study the curing of a model systema thiolene-chemistry-based prepolymer (NOA65) and its mixtures with liquid crystals. Curing reactions of NOA65 were examined as a function of the film thickness, temperature, and liquid-crystal content. While there was little dependence of the curing behavior on the thickness of the film, the effect of temperature was strong. Curing rates exhibit a maximum around 325 K, while conversions reach a plateau about 20 K higher. The effect of liquid-crystal addition reveals a depression in the conversion. However, compared to the neat matrix, the final conversion was found to be significantly lower only for phase-separating concentrations. The rate of reaction decreased, and the induction period for the onset of polymerizing reactions increased with increasing liquid-crystal concentration. Real-time FTIR spectroscopy ...

Studying Polymer-Dispersed Liquid-Crystal Formation by FTIR Spectroscopy. 2. Phase Separation and Ordering

Polymerization-induced phase separation to form polymer-dispersed liquid crystals (PDLCs) is a complex process involving simultaneous curing and phase separation to form nematic microdomains. Real-time FTIR spectroscopy has been used to simultaneously observe and quantify the curing process using a model systema fast photocurable matrix (NOA65) and a liquid crystal (E7). While the role of FTIR spectroscopy in monitoring chemical changes is well recognized and reinforced for PDLCs, it is demonstrated in this paper that it is also a powerful tool to monitor physical changes (phase separation and nematic ordering). Phase separation was detected during the curing process by a scattering-induced change in the absorbance spectrum of the sample. Nematic ordering could be observed and quantified based on a change in a characteristic band of the liquid crystal. Moreover, the phase separation and the onset of nematic ordering are temporally resolved. The conversion at phase separation decreases strongly with an increase in liquid-crystal content, while the conversion required for phase separation increases with increasing temperature. Isotropic droplets are formed followed by nematic ordering in the domains at lower E7 concentrations, while the processes are simultaneous for higher concentrations. Temperatures close to and above the LC transition temperature also lead to isotropic domains, which form nematic domains upon cooling. The fraction of liquid crystal present as nematic droplets and total fraction of nematic domains in the PDLC are quantified based on changes in the vibrational spectrum of E7. On the basis of mass balances applied to the closed process, the phase diagram of the system could be determined as a function of curing temperature. Solubility limits obtained by this method agree well with results obtained by other researchers. The concept of a spectroscopic composite plot that completely describes the formation process in a PDLC is proposed.

UV curable polyurethane-based microspheres

Radiation curable polyurethane-based microspheres were prepared by modifying conventional procedures for preparing anionic polyurethane dispersions. Vinyl groups were introduced to the side chains and the ends of the polyurethane main chains. Photoinitiators and multifunctional acrylate oligomers were incorporated into each microsphere. The curing behavior of the films obtained from these microspheres under UV were studied. The MEK resistance of UV cured films without multifunctional acrylate oligomers was raised when the content of vinyl groups is above a certain threshold value. The effect of the incorporation of multifunctional acrylates oligomers on MEK resistance was observed. This effect was remarkable at low UV irradiation intensity. The curing behavior of the films was followed by real time FT-IR spectroscopy. The accelerating effect of the incorporation of multifunctional acrylates became striking particularly at the early stage of curing process. Multifunctional acrylates were found to be effective in raising the extent of the conversion of the double bonds. The curing behavior under UV irradiation was compared with that under EB irradiation.

Spectroscopy of Hydrothermal Reactions 13. Kinetics and Mechanisms of Decarboxylation of Acetic Acid Derivatives at 100−260 °C under 275 bar

The rates and pathways of decarboxylation of acetic acid derivatives, RCO2H, and their Na+ salts, RCO2Na, which possess electron-withdrawing groups (R = CCl3−, CF3−, HOC(O)CH2−, NH2C(O)CH2−, CF3CH2−, NCCH2−, CH3C(O)−) were determined in H2O at 100−260 °C and a pressure of 275 bar. Simple conversion to RH + CO2 occurs in most cases, except that H2O appears to be a required reactant for the anions. Real-time FTIR spectroscopy was used to determine the rate of formation of CO2 in flow reactors constructed of 316 stainless steel (SS) and of titanium. With a few exceptions, the rate of decarboxylation is similar within the 95% confidence interval in 316 SS and Ti and the difference is smaller than that caused by R. Therefore, while wall effects/catalysis may exist in some cases, it plays a lesser role in the relative rates than the substituent R. The acid form of the keto derivatives decarboxylates more rapidly than the anionic form, whereas the reverse is true for the nonketo derivatives. In keeping with the ...

Mechanistic aspects of the thermal mer-to- fac isomerization of mer-[Mn(X)(CO) 3( α-diimine)] (X=Cl, Br, I)

The thermal mer-to- fac isomerization of the photochemically generated complexes mer-[Mn(X)(CO) 3( α-diimine)] (X=Cl, Br, I, α-diimine= N,N′-diisopropyl-1,4-diazabutadiene ( iPr-DAB); X=Br, α-diimine=4,4′-dimethyl-2,2′-bipyridine (bpy′), pyridine-2-carbaldehyde- N-isopropylimine ( iPr-PyCa), 2,3-dipyrid-2′-ylpyrazine (dpp), and R-DAB (R= cPr, iPr, tBu)) was investigated by real-time (RT) FTIR spectroscopy at various temperatures and in different solvents. In addition, the fac- and mer-isomers were also studied by UV–vis spectroscopy. The intricate isomerization process has been characterized by determination of (i) (pseudo) first-order rate constants from linear ln(A oo–A t) versus time plots, and (ii) the corresponding thermodynamic activation parameters ΔS ‡ and ΔH ‡ from Eyring plots. For mer-[Mn(Br)(CO) 3(bpy′)] in THF the kinetic and thermodynamic data are consistent with a mechanism which probably involves association of THF and partial dissociation of the Br − ligand. In contrast with this, the rapid isomerization of the complexes mer-[Mn(X)(CO) 3(R-DAB)] (X=Cl, Br; R= iPr, and X=Br; R= cPr, iPr, tBu) with the highly flexible electron-withdrawing R-DAB ligands follows a dissociative course probably involving cleavage of a Mn–N bond. These major reaction pathways have been employed to explain the isomerization of the other complexes under study, viz. mer-[Mn(X)(CO) 3( α-diimine)] (X=Br; α-diimine= iPr-PyCa, dpp, or X=I; α-diimine= iPr-DAB).

Real-Time FTIR and in Situ Rheological Studies on the UV Curing Kinetics of Thiol-ene Polymers

Real-time FTIR spectroscopy and in situ dynamic rheology were used to characterize the UV curing kinetics of a thiol-ene system containing trimethylolpropane tris(2-mercaptoacetate) and trimethylolpropane diallyl ether. The combination of these two techniques offered a powerful approach for monitoring changes in the chemical and rheological properties of the system during UV curing. Comparable gel times were independently obtained from both FTIR spectroscopy and rheology, thereby validating the comparison of data obtained from each method. The thiol conversion determined from FTIR spectroscopy was correlated with the elastic modulus obtained from rheology. The conversion increased very rapidly during the initial stages of UV curing. However, the elastic modulus did not have an appreciable value until after 65% of the thiol functional groups have reacted, following which the elastic modulus increased at a rapid rate. From the Flory−Stockmayer theory of gelation, the critical thiol conversion at the gel poi...

Characterization of cure profiles of anaerobic adhesives by real-time FT-IR spectroscopy. Part II. Surface activation

A real-time Fourier transform-infrared (RT/FT-IR) spectroscopic technique has been used to study the cure profile of surface-activated anaerobic polymerization on metal surfaces at room temperature. The cure characterization of redox polymerization of anaerobic composition on several metal surfaces has been studied which included copper, aluminum, galvanized steel, zinc-plated steel, stainless steel, and passivated stainless steel. The copper surface was found to be the most active surface for initiating the polymerization. The effectiveness of various surface treatments for anaerobic cure was also studied. The results indicated that 316L stainless steel specimens, which have been passivated for corrosion preventive purposes, show an increase in activity for surface-initiated anaerobic polymerization over the specimen without passivation. The anaerobic cure on passivated 316L stainless steel specimens shows a higher ultimate degree of conversion and cure speed than on non-passivated steel. The buffing and passivation treatments produced the most active surface. This increase in surface activity appears to be due to the buffing and passivation treatment, resulting in roughening the surface as well as removing the inert oxide layer and scales. The role of nitric acid/EDTA in the passivation treatment for surface reactivity enhancement has also been discussed. The surface reactivity was evaluated based on the ability to accelerate an anaerobic cure in a real-time mode and has been correlated with the metal type and content in the interface region. The surface texture and metal contents were measured using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively.

Characterization of Cure Profile of Anaerobic Adhesives by Real-Time FT-IR Spectroscopy. I. Effect of Transition Metal Dithiolate Complexes

Abstract A model acrylic adhesive formulation consisting of triethylene glycol dimethacrylate (TRIEGMA) monomer, cumene hydroperoxide (CHP), o-benzoic sulfimide (saccharin or BS) and with or without a metal dithiolate catalyst has been made to study kinetics and mechanism of the anaerobic polymerization. In these studies, a real-time FT-IR spectroscopic (RT/FT-IR) technique has been used to study anaerobic cure profiles at room temperature. The catalytic effect of several transition metal dithio complexes for redox-initiated acrylate polymerization has been studied. The dithiolates used in these studies include the dithiocarbamate, xanthate dithiophosphate complexes of copper, nickel and zinc systems. Copper diacetylacetonate was also studied for comparison of its catalytic reactivity. A syner-gistic effect of copper dithiolate catalyst and saccharin was observed. The effects of catalyst concentration, metal and ligand type, and co-initiator on cure profiles have been monitored in a real-time mode.

ChemInform Abstract: Applications of Real‐Time FTIR Spectroscopy to the Elucidation of Complex Electroorganic Pathways: Electrooxidation of Ethylene Glycol on Gold, Platinum, and Nickel in Alkaline Solution.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.