Fiber optic mid-IR monitoring

Key words real-time fiber optic mid-IR monitoring, isobutylene, styrene, p-tert-butylstyrene, living polymerization, solution polymerization, suspension polymerization... 

Puskas JE, Tzaras E, Marr G, Michel AJ. Real-time fiber optic mid-IR monitoring of solution and suspension polymerizations. Abstr Papers ACS 2001 221 U315-U315. 

In summary, the results presented here demonstrate that the fiber optic ATR and TR FTIR methods developed in our laboratory can conveniently be used to monitor both homogeneous and heterogeneous polymerizations, and various ancillary reactions, yielding very useful information about these processes. Our research group has extensively been using the fiber optic mid-IR ATR-FTIR and TR-FTIR techniques for macromolecular engineering. ... 

Previous work of one of the authors dealt with mid IR monitoring of IB polymerization using fiber-optic equipment. Fourier transform near infrared spectroscopy can be accomplished without expensive hardware. It therefore seemed to be a desirable goal to combine the advantage of fiber optics with low-cost fibers available for measurements in the NIR range. The NIR spectrum of IB obtained after solvent subtraction (Figure 2) reveals at least three signals, which should be suitable for the determination of monomer conversion. 

Mid-IR fiber optics provides a convenient way to monitor many kinds of chemical reactions in situ and in real time. Isocyanate chemistry, both in the solution phase and in the form of urethane foams and binders, lends itself well to this approach. It is shown in this paper that the calibration of mid-IR fiber optics is simple and transferable between probes and probe heads, and that useful information about reaction rates and extent of cure can be obtained by simple peak area measurements in many cases. 

The monitoring of isocyanate reactions, including urethane formation in foams and binders, can be conveniently carried out using mid-IR fiber optic spectroscopy. Once the spectroscopic evolution of a particular reaction is understood, a simple measure of the degree of curing of a urethane material can be developed by using a ratio of peak areas for a characteristic peak arising from the precursor and one from the product. In case such as that of the simulated solid fuel discussed above, the small batch reactions used in the industry can be monitored in situ when this method is combined with the use of mid-IR fiber optics, which offer a combination of convenience and robust calibration. 

Since the mid-1990s, there has been plenty of activity regarding the use of spectroscopic techniques for on-line evaluation of polymer properties [143-146]. This has been possible due to the recent development of fiber-optic probes, which allow in-situ measurements in remote and harsh environments (high temperatures, pressures, toxic environments, and so on). An additional advantage is that a fiber-optic probe can be installed in an existing reactor within a short time without expensive modifications. Fluorescent, ultraviolet (UV), infrared (IR), near-infrared (NIR), mid-infrared (MIR) and Raman spectroscopic techniques can be used for polymerization reaction monitoring. These can be divided between absorption- and emission-based techniques. IR, NIR, and MIR are absorption-based. 

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