Real-time Infrared Spectroscopy Research Articles

Photochemistry and photoinduced chemical crosslinking activity of several type II commercial photoinitiators in acrylated prepolymers

Some of the most important commercial benzophenone and thioxanthone photoinitiators have been analysed by various spectroscopic techniques to evaluate the relationship between their photophysical properties and photoinitiation activity for photocrosslinking of commercial acrylated monomers and prepolymers. The type of electronic transitions occurring upon absorption of light are established via UV spectroscopy. Phosphorescence spectroscopy has been used to study their triplet energies and lifetimes and phosphorescence quantum yields. Microsecond flash photolysis has also been undertaken to determine the nature of the free radical semiquinone (ketyl) intermediates. The free radical intermediate decay kinetics of the different photoinitiators have also been determined, as well as the first and second order rate constants, the transient radical absorptions and radical lifetimes. Photocrosslinking studies have been undertaken by Real Time Infrared Spectroscopy (RTIR) at different photoinitiator concentrations in the presence and absence of oxygen using a low viscosity reactive diluent and a commercial resin of higher viscosity. Pendulum hardness measurements were also carried out to correlate the film hardness properties with the kinetic results obtained with RTIR. Analysis of the data shows that whilst type II initiator photoactivity is predominantly dependent upon the absorption maxima of the chromophore, structural influences play a major role in controlling the nature of the lowest excited triplet state and the formation of radical intermediates.

Kinetic Study of Ultrafast Photopolymerization Reactions

Abstract The photopolymerization kinetics of UV-curable polyurethane-acrylate resins has been studied by real-time infrared spectroscopy (RT-IR). From the conversion versus time curves recorded during and after UV exposure, the rate constants of propagation (kp ) and termination (kt ) reactions were determined at different stages of the curing process. The kp value was shown to remain fairly constant at about 104 L·mol−1·s−1, until 30% conversion, and to decrease later on due to gelation and related molecular mobility restrictions. The increasing viscosity of the medium undergoing polymerization was found to have a stronger effect on the kt value, which decreased rapidly from the very beginning of the irradiation. The proportionality of kp and kt , observed above 10% conversion was taken as evidence of a termination process occurring by a reaction diffusion mechanism. The rate of polymerization was found to increase with the light intensity up to an upper limit above which the reaction kinetics is not controlled by the initiation rate but only by the diffusion rate of the reactive species. The temperature profile has also been recorded by RT-IR spectroscopy and shown to correlate well with the cure profile. The increase of the temperature shows the same light intensity dependence as the polymerization rate and levels at a maximum value under very intense illumination.

Synthesis and photoinitiated cationic polymerization of 1,2,3-tris(1-propenoxy) propane

The synthesis of 1,2,3-tris (1-propenoxy) propane (GTPE) was carried out by the rearrangement of 1,2,3-tris(2-propenoxy) propane (glycerol triallyl ether, GTAE) and the Z: E isomer composition of the GTPE was determined using gas chromatography and 1HNMR. The photoinitiated cationic polymerization of the GTPE was studied using realtime infrared spectroscopy (RTIR). Employing the data from these studies, rates of polymerization for the respective E and Z propenyl ether double bonds were calculated. The rate of incorporation of Z-double bonds of GTPE into the crosslinked polymer matrix is 1.6 times that of E-double bonds. The effects of oxygen and several other free radical polymerization inhibitors were investigated. An increase in the photogel time and decrease of the gel-content in the presence of these inhibitors implicates the involvement of free radicals in the process of the generation of propagating cationic centers when diaryliodonium salt cationic photoinitiators are used. © 1994 John Wiley & Sons, Inc.

Kinetic study of light‐induced polymerization by real‐time UV and IR spectroscopy

AbstractReal time ultraviolet (RTUV) spectroscopy was used to study the photolysis kinetics of a radical‐type morpholino initiator, during the polymerization of a multiacrylate monomer exposed to UV radiation in bulk, in solution, in a polyurethane‐acrylate resin, and in a poly(methyl methacrylate) matrix. The photolysis rate constant k was determined from the exponential loss profile recorded; it was found to vary between 0.1 and 3s−1, depending on the light intensity and on the monomer concentration. The quenching of the photoinitiator excited states by the acrylate monomer was shown to be an important deactivation pathway which substantially reduces the rate of initiation. The observed influence of the film thickness and photoinitiator concentration on the k value were accounted for by the internal filter effect. Conversion versus time curves were recorded by real time infrared (RTIR) spectroscopy for the various systems examined, thus allowing a direct comparison of both the actual polymerization rate and the residual unsaturation content of the cured polymer. Various factors were shown to be responsible for the early stop of the polymerization, such as depletion of the photoinitiator, O2 inhibition, or vitrification of the polymer. The photoinitiated cationic ring‐opening polymerization of a cycloaliphatic diepoxy monomer was also studied in real time by RTUV and RTIR spectroscopy. Despite a very fast photolysis of the triarylsulphonium initiator, the polymerization of the epoxy monomer developed less rapidly than for the acrylic monomer, with shorter kinetic chain lengths. A linear relationship was found to exist between the decay rate constant and the light intensity, for both the radical and the cationic photoinitiators, as expected for a direct photolysis process.

Lasers and Photopolymers

A general outline of new applications of lasers in polymer photochemistry is given. The fields covered include the kinetic and mechanistic study of various elementary processes (in solution model compounds) by laser spectroscopies and the extension of this approach to practical systems (solids or in polymerization samples, thin films) by holographic techniques or real‐time infrared spectroscopy. Stress is laid on the great importance of laser techniques in understanding the fundamental aspects of the processes involved in polymer photochemistry.

Photopolymerisation de monomeres multifonctionnels—III. analyse cinetique par spectroscopie infrarouge resolue dans le temps (RTIR)

Real-time infrared (RTIR) spectroscopy was used to investigate the kinetics of the photopolymerization of multiacrylic macromonomers. This new technique allows the conversion to be recorded directly as a function of the exposure time, for reactions developing within a fraction of a second. The dependence of the rate of polymerization on the photoinitiator concentration, and on the conversion was determined. The radicals were shown to reach a stationary concentration of 10 −4 mol l −1 ca 100 msec after the beginning of the u.v. exposure, at which time the polymerization reaches its maximum rate. At the end of the irradiation, the reaction continued in the dark, accounting for up to 90% of the total polymer formed. The rate constants of propagation ( k p) and termination ( k t) were determined directly from the polymerization profile recorded upon u.v. exposure and in the dark. For the most reactive system, made of a polyurethane-diacrylate and an oxazolidone-acrylate, the polymerization quantum yield exceeded 20,000 mol. photon −1, corresponding to a kinetic chain length of 50,000 acrylic functions polymerized per initiating radical.

US 4,704,414 filler

This paper reported a photocleavage type polymerizable organosilicon macromolecular photoinitiator (HHMP-Si-CC), which was synthesized based on traditional photoinitiator 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl propan-1-one (HHMP) and amino polysiloxane. HHMP-Si-CC cannot only spontaneously form a concentration gradient in the photopolymerization system, initiate gradient photopolymerization and effectively mitigate inhibition of oxygen, but also overcome the migration of photolysis fragments of the photoinitiator from UV-curable material. Its structure was confirmed by proton nuclear magnetic resonance (1H NMR), 13C NMR, 29Si NMR and Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The kinetics of photopolymerization of HHMP-Si-CC was studied by real-time infrared spectroscopy (RTIR). Moreover, it was proved by X-ray photoelectron spectroscopy (XPS) and UV absorption that HHMP-Si-CC had relatively good self-floating ability. The polymer initiated by HHMP-Si-CC presented a gradient change in the degree of polymerization, molecular weight, thermostability and glass transition temperature (Tg). The surface morphology of poly(triethylene glycol diacrylate) (PTPGDA) initiated by HHMP-Si-CC was studied by scanning electron microscopy (SEM). More importantly, the migration of photolysis fragments of the HHMP-Si-CC from UV-curable materials was also investigated by high performance liquid chromatography (HPLC). The results showed that the migration more was effectively mitigated by introducing polymerizable groups into the HHMP-Si-CC. HHMP-Si-CC should have potential applications for preparing more environmentally friendly gradient materials.