A detailed investigation of the liquid-state polymerization of diacetylenes by calorimetric (DSC) and spectroscopic (in situ EPR) thermal analysis techniques is performed. Isoconversional kinetic analysis of the calorimetric data reveals that liquid-state polymerization is governed by a well-defined rate-limiting step as evidenced by a nearly constant isoconversional activation energy. By comparison, solid-state polymerization demonstrates isoconversional activation energy that varies widely, signifying multistep kinetics behavior.
View Article and Find Full Text PDFTwo flexible α-azide-ω-alkynes differing in the length of the hydrocarbon spacers (C vs. C) between functional groups are synthesized. Their bulk polymerization kinetics is studied by differential scanning calorimetry (DSC) and parameterized with the aid of isoconversional methodology.
View Article and Find Full Text PDFPhys Chem Chem Phys
April 2023
Bulk azide-alkyne cycloaddition between 1-azidodecane and phenyl propargyl ether is studied in detail under the conditions of linear heating. The reaction mechanism involves two parallel channels that respectively yield isomeric 1,4- and 1,5-adducts. Remarkably, the ratio of the isomer amounts remains practically the same at different heating rates.
View Article and Find Full Text PDFPolymers (Basel)
December 2022
The Jeziorny method treats nonisothermal crystallization data by replacing the variable temperature () values with the corresponding values of time and substituting them into the isothermal Avrami plot, ln[-ln(1 - )] vs. ln. For isothermal data, the slope of this plot is the Avrami exponent, and the intercept is the rate constant, .
View Article and Find Full Text PDFThis study highlights the value of nonisothermal kinetic methods in selecting temperature conditions for the isothermal preparation of microporous polymeric materials. A dicyanate ester is synthesized and the kinetics of its polymerization in diphenyl sulfone are studied by calorimetry under nonisothermal conditions. The kinetics are analyzed by a model-based approach, using the Kamal model, as well as by a model-free approach, using an advanced isoconversional method.
View Article and Find Full Text PDFOzawa has modified the Avrami model to treat non-isothermal crystallization kinetics. The resulting Ozawa-Avrami model yields the Avrami index () and heating/cooling function (()). There has been a number of recent applications of the Ozawa-Avrami model to non-isothermal crosslinking polymerization (curing) kinetics that have determined and have used () in place of the rate constant (()) in the Arrhenius equation to evaluate the activation energy () and the preexponential factor ().
View Article and Find Full Text PDFArtificial neural networks (ANNs) are a method of machine learning (ML) that is now widely used in physics, chemistry, and material science. ANN can learn from data to identify nonlinear trends and give accurate predictions. ML methods, and ANNs in particular, have already demonstrated their worth in solving various chemical engineering problems, but applications in pyrolysis, thermal analysis, and, especially, thermokinetic studies are still in an initiatory stage.
View Article and Find Full Text PDFA new rigid tricyanate ester consisting of seven conjugated aromatic units is synthesized, and its structure is confirmed by X-ray analysis. This ester undergoes thermally stimulated polymerization in a liquid state. Conventional and temperature-modulated differential scanning calorimetry techniques are employed to study the polymerization kinetics.
View Article and Find Full Text PDFThe kinetics of thermally stimulated processes in the condensed phase is commonly analyzed by model-free techniques such as isoconversional methods. Oftentimes, this type of analysis is unjustifiably limited to probing the activation energy alone, whereas the preexponential factor remains unexplored. This article calls attention to the importance of determining the preexponential factor as an integral part of model-free kinetic analysis.
View Article and Find Full Text PDFThis study investigates the kinetics of confined polymerization of bisphenol E cyanate ester in the nanopores of the three types of silica colloidal crystals that differ in the concentration and acidity of the surface-grafted proton-donor groups. In all three types of pores, the polymerization has released less heat and demonstrated a very similar significant acceleration as compared to the bulk process. Isoconversional kinetic analysis of the differential scanning calorimetry measurements has revealed that the confinement causes not only a dramatic change in the Arrhenius parameters, but also in the reaction model of the polymerization process.
View Article and Find Full Text PDFThe Kissinger method is an overwhelmingly popular way of estimating the activation energy of thermally stimulated processes studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA), and derivative thermogravimetry (DTG). The simplicity of its use is offset considerably by the number of problems that result from underlying assumptions. The assumption of a first-order reaction introduces a certain evaluation error that may become very large when applying temperature programs other than linear heating.
View Article and Find Full Text PDFThe objective of this review paper is to survey the phase transition kinetics with a focus on the temperature dependence of the rates of crystallization and melting, as well as on the activation energies of these processes obtained via the Arrhenius kinetic treatment, including the treatment by isoconversional methods. The literature is analyzed to track the development of the basic models and their underlying concepts. The review presents both theoretical and practical considerations regarding the kinetic analysis of crystallization and melting.
View Article and Find Full Text PDFDifferential scanning calorimetry is used to obtain insights into the kinetics and thermodynamics of nanoconfined gelation. Gels of polyacrylonitrile in propylene carbonate, poly(vinyl alcohol) in ethylene glycol, and isotactic polypropylene in o-dichlorobenzene and decalin are studied in silica nanopores. Two major effects are observed for nanoconfined gels: a decrease in the heat of gelation and an increase in the gelation temperature.
View Article and Find Full Text PDFIn this tutorial overview article the authors share their original experience in studying the kinetics of thermally stimulated reactions under the conditions of continuous cooling. It is stressed that the kinetics measured on heating is similar to that measured on cooling only for single-step reactions. For multi-step reactions the respective kinetics can differ dramatically.
View Article and Find Full Text PDFThe purpose of this study is to highlight the surface and size effects of the nanopores on the thermodynamics and kinetics of gelation. The effects have been probed by applying differential scanning calorimetry to poly(vinylidene fluoride) solutions in tetraethylene glycol dimethyl ether (tetraglyme) and γ-butyrolactone. Nanoconfinement has been accomplished by introducing gels into native and organically modified silica nanopores (4⁻30 nm).
View Article and Find Full Text PDFThe present study explores the hypothesis that a polymer can affect the thermal stability of a drug in solid polymer-drug dispersions. The hypothesis is tested in a systematic fashion by combining isoconversional kinetic analysis with thermogravimetric measurements on several solid dispersions. Experimental systems involve three drugs: indomethacin (IMC), felodipine (FD), and nifedipine (ND) and their solid dispersions with polyvinylpyrrolidone (PVP).
View Article and Find Full Text PDFMacromol Rapid Commun
January 2019
This article surveys some exciting possibilities and results offered by less common, yet essential applications of differential scanning calorimetry and thermogravimetric analysis (TGA). The applications are concerned with the most commonly studied processes of the glass transition, crystallization, melting, polymerization, and degradation. Issues related to the glass transition include the non-Arrhenius temperature dependence and fragility, kinetic complexity of physical aging, evaluation of cooperatively rearranging regions, and rigid amorphous fraction.
View Article and Find Full Text PDFMacromol Rapid Commun
February 2018
It is demonstrated that differential scanning calorimetry can measure the kinetics of the thermally initiated polymerization during continuous cooling. The measurements are accomplished by switching from fast heating to much slower cooling. The study is exemplified by crosslinking polymerization (curing) of diglycidyl ether of bisphenol A epoxy and m-phenylenediamine taken in stoichiometric and nonstoichiometric ratios and measured under heating and cooling conditions.
View Article and Find Full Text PDFA mixture of triethylamine and water is a lower critical solution temperature system that demixes (separates into individual phases) on heating. Differential scanning calorimetry has been applied to study the process of demixing in native and organically modified silica nanopores whose size varied from 4 to 30 nm. It has been found that in both types of nanopores, the temperature and enthalpy of demixing decrease significantly with decreasing the pore size.
View Article and Find Full Text PDFGlucose and fructose crystals undergo significant superheating during melting that allows one to study the kinetics of this process. Melting of both compounds has been studied by differential scanning calorimetry (DSC). The obtained data have been subjected to isoconversional kinetic analysis.
View Article and Find Full Text PDFThis study develops technology for mitigation of NO formed in thermal processes using recycled plastics such as polyethylene (PE). Experiments involve sample characterization, and thermogravimetric decomposition of PE under controlled atmospheres, with NO concentration relevant to industrial applications. TGA-Fourier transform infrared (FTIR) spectroscopy and NO chemiluminescence serve to obtain the removal efficiency of NO by fragments of pyrolyzing PE.
View Article and Find Full Text PDFThis article surveys the decade of progress accomplished in the application of isoconversional methods to thermally stimulated processes in polymers. The processes of interest include: crystallization and melting of polymers, gelation of polymer solutions and gel melting, denaturation (unfolding) of proteins, glass transition, polymerization and crosslinking (curing), and thermal and thermo-oxidative degradation. Special attention is paid to the kinetics of polymeric nanomaterials.
View Article and Find Full Text PDFNanoconfinement is a way to create materials whose properties differ from the bulk. For the first time, this research explores the effect of nanoconfinement on the thermodynamics and kinetics of gel melting. Differential scanning calorimetry has been employed to study gelatin gels prepared inside 4, 6, 15, and 30 nm pores of a silica matrix.
View Article and Find Full Text PDFPhys Chem Chem Phys
November 2016
The research presented in this paper is devoted to the intriguing phenomenon of thermal decomposition that takes place during continuous cooling after being initiated by heating to higher temperature. This paper describes the principles of detecting this phenomenon and measuring its kinetics. As one of the possible ways, the process can be detected and its kinetics can be measured by means of differential scanning calorimetry provided that cooling is performed several hundred times slower than heating.
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