For these polymers, a thorough understanding of polymerization reactions and control of all reaction variables is crucial to producing a material that meets the end-use requirements and specifications.
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Polymers are macromolecules that consist of smaller repeating monomeric subsegments that are linked together to form chains. Polymers that exist in nature, such as polypeptides and polysaccharides, are critical components of living organisms. Synthetic polymers, such as nylon and polyurethane, have transformed how we manufacture and use commercial products. These latter polymers are typically formed by adding monomer segments together via free radical addition processes or through linking the segments together by condensation reactions that produce the polymer along with water or another small molecule.
This understanding involves factors including the kinetics of the reaction, monomer conversion rates and reactivity ratios, the relationship and influence of reaction parameters on the molecular weight and distribution, a thorough understanding of polymerization mechanism in initiation, propagation and termination phases and ensuring that the overall polymer structure meets the target application need.
In more complex polymerizations such as copolymer or multi-polymer, measuring the individual reaction rates of the different monomers allows researchers to both tune and ensure the physical properties of the final product. Understanding critical polymer reaction parameters can lead to precise control of multi-step polymerizations, real-time residual monomer measurements, and ultimately improved end-use polymer properties. Well-regulated polymerization reactions yield molecules that are well-characterized with respect to composition, molecular weight, molecular weight distribution, structural and physical properties.
To achieve this, it is necessary to understand and carefully control the many chemical and reaction parameters associated with the synthetic process. Infrared spectroscopy has proven to be highly valuable for meeting this challenge. Real-time, in situ FTIR measurement has proven particularly valuable to provide insight into key kinetic, mechanistic and chemical structure information, while eliminating the difficulties associated with off line measurements of polymerizations reactions. Over the past three decades, the investigation of polymerization reactions from the lab through scale-up to production has been one of the most prolific and valued uses for in situ FTIR technology.
Real-time, in situ FTIR Spectroscopy provides enhanced knowledge and improved performance in the investigation of polymerization reactions:. Schultz, A. Anionic polymerization is a widely used chain growth method for producing thermoplastic elastomers and many hundred thousand tons of material is made every year using this process. In this article, the scientists report the development of a new class of phosphorus-containing styrenic ABC triblock copolymers. ABC triblock copolymers are formed by linking three different monomers and in this case, those monomers are styrene S , isoprene I and 4-diphenylphosphino styrene DPPS.
The scientists report that sequential addition of these monomers via anionic polymerization yields a high-performance polymer that can be fine-tuned with regard to molecular weights and molecular weight uniformity. Understanding kinetics and adjusting fine-tuning reaction variables is critical to produce a material with targeted performance. Deng, Z. Shen, L. Li, H. Sci Polytetrahydrofuran is a widely used industrial polymer that is formed via a cationic ring-opening reaction. The reaction tends to proceed rapidly with a number of factors influencing yield and molecular weight of the final product.
For this reason, it is important to understand the kinetics and thermodynamics of the reaction. The scientists involved in this study decided to investigate this important ring-opening reaction with ReactIR technology. They pointed out that this polymerization reaction had been studied previously by a number of off-line analytical methods including gravimetric analysis, NMR, GC, UV-Vis and dilatometry.
As the reaction proceeds, the increasing viscosity makes off-line sampling increasingly problematic and therefore these earlier investigations focused on initial stages of the polymerization reaction. They found that using in situ, real-time analysis is a better means to study this polymerization since it improves measurement accuracy, eliminates the time and difficulty associated with off-line sampling and most importantly, gives a more complete understanding of the reaction kinetics and thermodynamics.
For this polymerization study, they recorded the reaction process through all stages and studied the effect of variables such as temperature and initiator concentration on the reaction kinetics. Long describes how in situ FTIR impacted polymer synthesis research.
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The technology allowed his group to determine real-time kinetics, reactivity ratios, and activation energies on the polymerizations reactions studied. This presentation highlights the in situ FTIR monitoring of various chain growth polymerization processes for the determination of reactivity ratios during copolymerization. FTIR is well suited for chain growth addition involving olefinic monomers. Plus, the addition of various nucleophiles using click reactions with a focus on the Michael addition reaction is described.
Spectroscopy during peroxide decomposition also permits the determination of half-life times during nitroxide mediated polymerization. In addition to chain growth polymerizations, in situ FTR is well suited for the monitoring of isocyanate composition in the formation of urethanes.
In Situ FTIR Spectroscopy provides continuous monitoring of key polymerization species monomers and polymers , and provides valuable information on polymerization reaction kinetics. With real-time, in situ ReactIR, the individual monomers used in co- and ter-polymerization reactions can be tracked in real-time enabling decisions about the reaction to be made immediately throughout the experiment. The control of the relevant parameters including additions can be automated and pre-programmed, so experiments can be safely run while recording all polymerization reaction parameters, 24 hours a day.
The individual steps of the process of the polymerization reaction together with the experimental data are continuously recorded and stored securely making them available for evaluation and interpretation. Due to the safe, highly accurate, and precise measurement and control, the number of experiments required is reduced making scale-up efficient.. In polymerization reactions, the impact of process parameters on droplet size are important factors to consider.
Traditionally, this has been estimated using offline methods. However, such an approach can be can be difficult and unsafe.
Polymerization - Wikipedia
Inline monitoring with ParticleTrack and ParticleView allow droplets to be monitored in real time and enable operators to act decisively in the plant environment to ensure product specifications are met. Key kinetic mechanisms such as coalescence and breakage can be quantified in real time enabling users to understand the impact of changing process parameters and ensure batch-to-batch repeatability.
Recent articles describing the use of Inline Particle Characterization in polymerization reactions:. Isocyanates are critical building blocks for high performance polyurethane-based polymers that make up coatings, foams, adhesives, elastomers, and insulation.
Concerns over exposure to residual isocyanates led to new limits for residual isocyanates in new products. Traditional analytical methods for measuring the residual isocyanate NCO concentration using offline sampling and analysis raise concerns. In situ monitoring with process analytical technology addresses these challenges and enables manufacturers and formulators to ensure that product quality specifications, personnel safety, and environmental regulations are met.
In situ chemical reaction kinetics studies provide an improved understanding of reaction mechanism and pathway by providing concentration dependences of reacting components in real-time.
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Continuous data over the course of a reaction allows for the calculation of rate laws with fewer experiments due to the comprehensive nature of the data. Reaction Progression Kinetics Analysis RPKA uses in situ data under synthetically relevant concentrations and captures information throughout the whole experiment ensuring that the complete reaction behavior can be accurately described. Scaling-up a chemical process from lab to manufacturing gives useful results only with accurate heat transfer coefficients.
Measuring the jacket and reactor temperature during the release of a well-defined amount of heat allows researchers to accurately compute the thermal resistance which is used to model the heat transfer and make critical predictions for reactors at larger scale.
Reaction calorimetry is essential to determine parameters that impact the heat transfer and the heat transfer coefficients to develop models to maximize the bandwidth of a manufacturing plant. Mixing is the reduction or elimination of inhomogeneity of phases that are either miscible or immiscible. Process scale-up and optimization require that the impact of mixing on the reaction rate be quantified.
This achieves the desired conditions required for the scale-up or scale-down of a process. Continuous flow chemistry opens options with exothermic synthetic steps that are not possible in batch reactors, and new developments in flow reactor design provide alternatives for reactions that are mixing limited in batch reactors. This can often result in better product quality and higher yield.
When coupled with Process Analytical Technology PAT , flow chemistry allows for rapid analysis, optimization, and scale-up of a chemical reaction. How can I be sure that my chemical process is safe? It is critical to understand the risks inherent in moving a chemical process to a larger scale before manufacturing begins.
The use of reaction calorimetry is an essential part of process development studies, providing detailed information about the rate of heat production. This allows researchers to optimize the temperature and dosing profiles to maximize process safety at all times, and reduce to a minimum the risks involved.
PAT transforms productivity, improves safety, and provides measurements for rapid troubleshooting. Process Analytical Technology PAT applications range from monitoring chemical reactions, crystallization, formulations, and bioprocessing. Transport and Logistics. Expertise Library. Literature: White Papers, Guides, Brochures. Additionally, the rise in viscosity also causes an increase of the reaction rate due to the gel effect. Suspension polymerizations present lower viscosities than bulk polymerizations because of the use of water as the continuous medium polymer particles are dispersed in the aqueous phase.
This lower viscosity of the continuous medium enhances the heat exchange capacity and, consequently, improves the temperature control of the reactor.
Photocatalysts in Polymerization Reactions
Besides that, in suspension polymerizations the ratio between the surface area of the polymer particles and the particle volume is much higher than the ratio between the thermal exchange area of the ampoules and the volume of the reaction medium of the bulk polymerizations. Therefore, the effective thermal exchange area of the suspension polymerization polymer phase is much higher than that of the bulk polymerization. Additionally, in bulk polymerizations, the thermostatic bath is kept at the desired reaction temperature, but the temperature of the reaction medium inside the ampoules does not remain constant due to the viscosity increase with the progress of the reaction, which causes a reduction in the thermal exchange efficiency.
These factors favor the appearance of a temperature gradient inside the ampoules and an increase in the average reaction temperature. The reaction temperature increase, in turn, favors an increase on the reaction rate, which helps to explain why the bulk polymerization rate is higher than the rate observed in styrene suspension polymerizations. The temperature of the reaction medium was recorded continuously during both polymerizations by a thermocouple coupled to a data acquisition board.
The thermocouple was placed inside an ampoule during the bulk reaction and immersed in the middle of the reaction medium during the suspension polymerization. Figure 3 shows the evolution of the temperature during both reactions. It can be observed that the temperature of the suspension polymerization decreased at the beginning of the reaction with the addition of the initiator dissolved in styrene and, a few minutes later, of DBSS and PVP, which were all fed at room temperature to the reactor.
In order to verify if this difference between the reaction temperatures was sufficient to explain the difference observed in the conversion, simulations were carried out with a mathematical model of styrene homopolymerizations using the experimental temperature profiles obtained for both reactions see Appendix. Figure 4 compares simulation and experimental conversion results of both bulk and suspension polymerizations and a good agreement can be observed for both reactions. This indicates that the difference of reaction temperature observed between these two systems is able to explain the differences in the reaction rate.
Therefore, in homopolymerization reactions, the conversion can be estimated directly by Raman spectroscopy as the relation between the intensity of the spectra and monomer concentration is linear Santos et al. The precise off-line quantification of monomer conversion by gravimetry and the conversion monitoring during suspension polymerization reactions are quite difficult due to the high heterogeneity of the reaction medium and the tendency of the particles to agglomerate rapidly when stirring is stopped.
The major problem of gravimetry is to collect representative samples from the reactor. In contrast, Raman monitoring through the reactor window is non-invasive and, since no sampling is required, presents the advantage of the stirring, which avoids the decantation of polymer particles and reduces the heterogeneity of the medium.
Therefore, a dynamic filter was used. This filter was only applied after the collection of the first five Raman spectra 4 minutes and 15 seconds of reaction , and the five concentration values estimated up to this point were used in the first filter application. This procedure was applied successively after the acquisition of each new spectrum, the predicted value being corrected by the spline filter, using all the raw points evaluated up to that point.
It is important to emphasize that this filtering procedure was proposed for on-line use; therefore, the corrections are not applied backwards. The use of this filter is indicated to reduce the variability of the estimation Santos et al. Figure 6 shows the comparison between off-line gravimetric conversion measurements and Raman monitoring of conversion during a styrene suspension polymerization S2. In this figure an excellent agreement can be observed between Raman estimations and gravimetric data.
Gravimetric data were obtained up to 75 minutes of reaction. After this point, the valve located at the bottom of the reactor used to collect samples was obstructed with polystyrene and could not be used any longer. It is important to emphasize that the conversion estimations by Raman spectroscopy did not require any reference method.
In this way, one measurement method corroborates the results of the other one. The methodology employed in this work to determine the conversion evolution of a suspension polymerization reaction by gravimetry was quite effective, as confirmed by the good agreement with on-line conversion monitoring using Raman Spectroscopy. This occurs due to the non-homogeneous thermal effects of the bulk reaction even for systems where the gel effect is not very pronounced. The effect of the differences in the reaction temperature on the evolution of conversion was also confirmed by simulation results.
Therefore, caution is recommended when bulk polymerization in ampoules is used for the kinetic study of styrene suspension polymerization, since in this latter case the reaction temperature control is much more effective and, consequently, the reaction rate does not follow the same course as in the bulk polymerization in ampoules. Alvarez, J. Bishop, R. Brandrup, J. Henning, B. Hergeth, W. Industrial process monitoring of polymerization and spray drying processes.
Polymer Reaction Engineering, 11, p. Hui, A. Kiparissides, C. Klodt, R. Priddy Eds. Machado, R. Maschio, G. Petzold, L. Reis, M. Search for books, journals or webpages All Pages Books Journals. View on ScienceDirect. Editors: Masoud Soroush. Paperback ISBN: Imprint: Elsevier. Published Date: 24th October Page Count: For regional delivery times, please check When will I receive my book?
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