Infrared Spectroscopy kinetics, polymerization

Polymerization Kinetics and Cure Studies [2,4,25] Infrared spectra of monomers differ markedly from spectra of the polymers [2], As a consequence, it is possible to use infrared spectroscopy to follow the course of polymerization reactions and to simultaneously analyze the structure of the polymer [2]. 

The polymerization kinetics of the bisbenzocyclobutene diketone monomer 14 (Fig. 10) were studied in the melt at various temperatures by infrared spectroscopy [48]. This technique has the advantage that it is relatively insensitive to the physical state of the system as it proceeds from monomer melt through the gel point and into the vitreous state. In addition, quantitative... 

In order to optimize the structure and properties of composites, a knowledge of the polymerization kinetics and mechanism are required. Various approaches have been taken to a determination of the kinetics of the polymerization including infrared spectroscopy 30,31). Although the various epoxide/anhydride/amine systems are... 

The first coupling of a LINAC with infrared spectroscopy has been performed by Palmese et al. in order to study in situ kinetics of radiation-induced cationic polymerization of epoxy systems. The aim of the study is to understand the curing behavior of polymers under irradiation. A UV light source and an electron beam (10 MeV pulse width of the beam from 2.5 to 10 pm) are coupled to a portable near infrared (NIR) instrument. Briefly, a portable NIR spectrometer (Control Development Incorporated, South Bend, IN, USA) is used,... 

Most studies of the kinetics of the isocyanate-hydroxyl reacfion have been done in systems composed of monofunctional reactants in various solvents (2 ). Even in these ideal systems, which have little resemblance to the more complicated polyurethane formulations, the reaction mechanism and kinetics are not well understood especially for the catalyzed reaction. This coupled with the added complexities encountered in polyurethane systems requires empirical determination of kinetic data if conversion during polymerization is to be predicted. A few kinetic studies on simple polyurethane systems have been reported (3, 4 ). Infrared spectroscopy was used to measure reaction rates in low catalyst formulations (3) while adiabatic temperature rise methods have been used to study fast systems (3 4, 5 ). 

The rate of polymerization and the cure penetration can be further increased by employing powerful lasers as radiation source, the exposure time dropping then into the millisecond range. Polymer relief images were thus obtained at micronic resolution by simply scanning the photosensitive plate with a highly focused laser beam. The kinetic profiles of such ultrafast reactions were directly record by using time-resolved infrared spectroscopy which allows instantaneous evaluation at any moment of the actual rate of polymerization and the precise amount of residual unsaturation in the cured polymCT. 

Alternatively, samples can be withdrawn from the reactor and analyzed for residual monomer in solution at various times by chromatographic or spectroscopic techniques. Sample removal techniques can be very difficult, especially since many reactions are extremely sensitive to oxygen and other impurities that can be introduced during sampling. In situ infrared spectroscopy is a state-of-the-art, real-time, monitoring technique that is well suited to obtain real-time structural and kinetic information of polymerization processes without sampling. In addition, reactions are analyzed without complicated reactor modifications or expensive deuterated monomers. 

T E Long, H. Y. Liu, B. A. Schell, D. M. Teegarden and D. S. Uerz, Determination of Solution Polymerization Kinetics by Near-infrared Spectroscopy. 1. Living Anionic Polymerization Processes, Macromolecules 26 6237 (1993). 

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

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... 

Long TE, Liu HY, Schell BA, Teegarden DM, Uerz DS. Determination of solution polymerization kinetics by near-infrared spectroscopy. 1. Living anionic-polymerization process. Macromolecules 1993 26 6237-6242. 

Souza FG, Anzai TK, Rodrigues MVA, Melo PA, Nele M, Pinto JC. In situ determination of aniline polymerization kinetics through near infrared spectroscopy. J Appl Polym Sci 2009 112 157-162. 

However, when monitoring and controlling polymerization reactors, one would like to get not only global reaction kinetics, but also information related to the state variables of the reactor namely, the concentration of monomer(s), polymer (conversion), concentration of radicals, molar masses, and so on. Obviously, this information cannot be directly obtained from the heat of reaction, bnt for some cases, the use of simple polymerization models in combination with the heat of reaction allows the state variables to be monitored noninvasively in real time and at mnch lower cost than when using dedicated instruments (near-infrared spectroscopy, mid-range infrared spectroscopy, Fourier transformed infrared spectroscopy, and/or Raman spectrometers). 

Rodriguez-Guadairama LA. Application of online near infrared spectroscopy to study the kinetics of anionic polymerization of butadiene. Eur Polym J 2007 43 928-937. 

Block copolymerization of PCL and PPEs can be performed with the initiation of Al(0 Pr)3. In a typical example, the polymerization of s-CL was initiated by A3 in THF, followed by the addition of phosphoester monomer (eqn [3]). The actual formation of the expected block copolymers was confirmed by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). Kinetic studies revealed that the of PPE follows a linear relationship with monomer conversion (up to 94.3%), and the molecular weight distribution remains narrow with dispersity (PDI) around 1.2, indicating that a limited amount of inter- or intramolecular transesterification reactions occurred. This enables the synthesis of block copolymers with narrow molecular weight distribution, controlled molecular weights, and adjustable compositions. 

Further addition of olefin to the product is impeded by steric factors. Equation (11) represents the initiation step of an anionic polymerization of an olefin (68) the rate of chain propagation in this case is very slow. It is important that the kinetics of Eq. (11) be thoroughly established, since it does form a prototype system for initiation of anionic polymerization. Preliminary work in the writer s laboratory (69) with ethylithium concentrations of about 0.1 M and 1,1-diphenylethylene concentrations of about 0.05 M, employing infrared spectroscopy to follow the disappearance of 1,1-diphenylethylene, have yielded second-order rate plots. The apparent order in alkyllithium, based on the method of initial rates, is in the range 0.7 to 0.95. The experimental details given by Evans and George indicate that meticulous care was taken in their work. It is possible, however, that the spectrophotometric method employed in following the reaction involves some hidden source of error, or that the difference in the experimental results is due to concentration differences. In any case, further work on this important system is desirable. 

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. 

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