Real-time infrared

Chang SC, Ho Y, Weaver MJ. 1992. Applications of real-time infrared spectroscopy to electrocatalysis at bimetallic surfaces. I. Electrooxidation of formic acid and methanol on bismuth-modified platinum (111) and platinum (100). Surf Sci 265 81-94. 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

To evaluate the reactivity of model compounds III-VIII in photoinitiated cationic polymerization, we have employed real-time infrared spectroscopy (RTIR). Thin film samples of the model compounds containing 0.5 mol% of (4-n-octyloxyphenyl)phenyliodonium SbF - as a photoinitiator were irradiated in a FTIR spectrometer at a UV intensity of 20 mW/cm2. During irradiation, the decrease in the absorbance of the epoxy ether band at 860 cm-1 was monitored. 

K.S. Anseth, C. Decker and C.N. Bowman, "Real-time infrared characterization of... 

Real-time infrared spectroscopy (RTIR) (21). The basic principle of this analytical technique consists of exposing the sample simultaneously to the polymerizing UV beam and to the analyzing IR beam, and monitoring on a high speed recorder the sharp decrease of the acrylic absorbance at 812 cm l. Conversion versus time curves have thus been recorded for the first time for photopolymerizations that develop extensively in a fraction of a second (211. If the reaction time drops into the millisecond range, a transient memory recorder (221 or an oscilloscope with storage function can be used to shorter the time resolution further. 

Introduction to Real Time Infrared Spectroscopic Monitoring... 

Kinetic Study of Photoinitiated Polymerization Reactions by Real-Time Infrared Spectroscopy... 

This is not the case of real-time infrared (RTIR) spectroscopy, " a technique that permits one to look at the chemical processes by monitoring in situ the disappearance of the monomer reactive group upon UV exposure. By this technique conversion versus time curves have been directly recorded for polymerizations occurring within a fraction of a second. RTIR spectroscopy proved also well suited to study the photopolymerization of monomer mixtures, which leads to the formation of copolymers or interpenetrating polymer networks, as it allows the disappearance of each type of monomer to be accurately followed in the course of the reaction. The performance of the three analytical techniques most commonly used to follow in real time high-speed photopolymerizations are summarized in Table 1. 

Figure 17 Performance of real-time infrared spectroscopy for kinetic analysis of high-speed photopolymerization reactions...

In silicone acrylates under inert conditions benzoyl addition on double bonds has been observed [2]. Using the real-time infrared technique (RTIR) one can show that the rate of initiator photolysis (Ro) is proportional to the rate of the formation of addition product. Moreover, the polymerization rate (Rp) is directly proportional to the rate of initiator photolysis [2] (Eq. 1), where [M] is the molar concentration of double bonds, [MJ is the initial concentration of double bonds, t is the time, A (jr), and k x) are conversion (x) dependent quantities, lo is the intensity of the incident light, and is the reaction rate of the a-cleavage a and P are exponents. 

No.ll, 22nd May 1995, p.4040-3 REAL-TIME INFRARED CHARACTERISATION OF REACTION DIFFUSION DURING MULTIFUNCTIONAL MONOMER POLYMERISATIONS Anseth K S Decker C Bowman C N Colorado,University Ecole Nationale Superieure de Chimie de Mulhouse... 

Thus, the applicability of real time infrared spectroscopy for monitoring high-speed photopolymerizations allows determining the rate of polymerization and the final monomer conversion. This can be used with either thin or ttiick samples exposed to intense polychromatic radiations. 

The photoinitiated polymerizations were followed by real-time infrared spectroscopy on thin films, radiation. The rates of polymerization were reported by them to increase with the light intensity according to a nearly square root law, up to an upper limit. The upper limit or the saturation effect was attributed by them to a fast consumption of flie photoinitiator under intense illumination. A strong correlation was found to exist between flie rate at which the temperature increases and fire rate of polymerization. The temperature shows the same light intensity dependence as the reaction rate, and levels off to a maximum value under intense illumination. Photopolymerization experiments carried out at a constant temperature of 25"C show that thermal runaway is not responsible for the increase of the polymerization rate observed at the beginning oftheUV exposure. 

The experimental procedure involves initiation of the polymerization by irradiation followed by cutting off the light after a certain time at a degree of conversion chosen, and monitoring the reaction in the dark. As experimental methods, both isothermal differential scanning calorimetry (photocalorimetry, photo-DSC) [2,6, 7, 18-32] and real-time infrared... 

Decker, C. and Moussa, K., A new method for monitoring ultrafast photopolymerization by real-time infrared spectroscopy, Makromol. Chem., 1988,189, 2381-2394. 

Free-radical cyclopolymerization of diallyl or mixed allyl-vinyl and allyl-acrylic derivatives has been investigated. Particularly, Jansen has studied the photo-initiated copolymerization of various commercial vinylethers as well as allylethers with fumarates or maleates. Real-time infrared spectroscopy with advanced multivariate statistical techniques was used for the determination of copolymerization reactivity ratios of... 

Unfortunately, DPC instruments do not have sufficient response time to follow the very fast rate of free radical photochemical reactions encountered in rapid processing environments. As shown in Fig. 2.80 the time to 90% cure of a UV curable resin at a UV intensity of 400mW/cm is about one second at room temperature. This fast kinetic measurement was carried out by a technique known as real time infrared spectroscopy (RT-IR). By this method one follows quantitatively the development of cure by tracking the disappearance of unsaturation as a decrease in the area of an absorbance band that was initially associated with the uncured resin (Decker and Moussa, 1988). The data in Fig. 2.80 indicates that a power compensation DSC begins to give accurate conversion data when UV intensities are of the order of lOmW/cm or less for this resin. Importantly, the data also show that the free radical polymerization of this UV curable resin can be fitted to a linear log-log plot of time versus intensity over a range of intensities of nearly five orders of magnitude. It is... 

Photoinitiated Cationic Polymerization. The cationic photopolymerization of the monomers synthesized above was studied using real-time infrared spectroscopy (RTIR).i This technique involves monitoring the decrease of an IR absorption characteristic of the functional group undergoing polymerization. In these studies, 2 mol % (4-decyloxyphenyl)phenyliodonium SbF was used as the photoinitiator. Figure 4 gives individual plots of the percent conversion of the various Tg monomers as a function of time at the optimum photoinitiator concentration for each of the monomers. The rate of photopolymerization of 1-propenyl ether functional monomer IX is the fastest followed by III, V and VI. 

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