Cure kinetics of carbon nanotube/tetrafunctional epoxy nanocomposites by isothermal differential scanning calorimetry

The cure kinetics of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) and 4,4′‐diaminodiphenylsulfone (DDS) as a cure agent in nanocomposites with multiwalled carbon nanotubes (MWNTs) have been studied with an isothermal differential scanning calorimetry (DSC) technique. The experimental data for both the neat TGDDM/DDS system and for epoxy/MWNTs nanocomposites showed an autocatalytic behavior. Kinetic analysis was performed with the phenomenological model of Kamal and a diffusion control function was introduced to describe the cure reaction in the later stage. Activation energies and kinetic parameters were determined by fitting experimental data. For MWNTs/epoxy nanocomposites, the initial reaction rates increased and the time to the maximum rate decreased with increasing MWNTs contents because of the acceleration effect of MWNTs. The values of the activation energies for the epoxy/MWNTs nanocomposites were lower than the values for the neat epoxy in the initial stage of the reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3701–3712, 2004     

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between T_g and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 773–783, 1998     

Isothermal cure kinetics of epoxy/phenol‐novolac resin blend system initiated by cationic latent thermal catalyst

The investigation of the cure kinetics of a diglycidyl ether of bisphenol A (DGEBA)/phenol‐novolac blend system with different phenolic contents initiated by a cationic latent thermal catalyst [N‐benzylpyrazinium hexafluoroantimonate (BPH)] was performed by means of the analysis of isothermal experiments using a differential scanning calorimetry (DSC). Latent properties were investigated by measuring the conversion as a function of curing temperature using a dynamic DSC method. The results indicated that the BPH in this system for cure is a significant thermal latent initiator and has good latent thermal properties. The cure reaction of the blend system using BPH as a curing agent was strongly dependent on the cure temperature and proceeded through an autocatalytic kinetic mechanism that was accelerated by the hydroxyl group produced through the reaction between DGEBA and BPH. At a specific conversion region, once vitrification took place, the cure reaction of the epoxy/phenol‐novolac/BPH blend system was controlled by a diffusion‐control cure reaction rather than by an autocatalytic reaction. The kinetic constants k₁ and k₂ and the cure activation energies E₁ and E₂ obtained by the Arrhenius temperature dependence equation of the epoxy/phenol‐novolac/BPH blend system were mainly discussed as increasing the content of the phenol‐novolac resin to the epoxy neat resin. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2945–2956, 2000     

Ring-opening polymerization of 1,5-dioxepan-2-one initiated by a cyclic tin–alkoxide initiator in different solvents

Ring-opening polymerization of 1,5-dioxepan-2-one initiated by 1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacyclodecane was carried out in chloroform, dichloromethane, or 1,2-dichloroethane. Effects of reaction temperature, solvent, and monomer-to-initiator ratio were investigated. Polymerization kinetics showed a first-order dependence on the monomer for polymerization in chloroform and dichloromethane at 40°C. The kinetic order with respect to the initiator were a first order when dichloromethane was used as the solvent, the order in initiator changed, depending on the initiator concentration when chloroform was used. A maximum in molecular weight was observed at 40°C when chloroform was used as the solvent. The change of solvent did not markedly alter the polymerization rate or the molecular weight of the polymers prepared, as expected from the coordination insertion mechanism. Depolymerization of the polymers formed was observed when the reaction was allowed to continue after complete monomer conversion in chloroform as reaction medium at 40°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3407–3417, 1999     

Kinetic investigations of formation of polyimides containing arylene sulfone ether linkages by potentiometric titration and their characterization

In this work, thermal solution imidization kinetics of two high performance polyimides, prepared from the polycondensation of pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with 4,4′-bis(3-aminophenoxy)diphenylsulfone (DAPDS) were investigated using nonaqueous titration technique with tetramethylammonium hydroxide. Most of the kinetic investigations, found in the literature, are based on the aromatic p-diamines.^1,2 In the present work, attention was focused on imidization kinetics with m-substituted aromatic diamines having electron donating ( O ) and electron withdrawing ( SO₂ ) groups in the same molecule. Kinetic parameters, namely the rate constants, activation energies, entropies and enthalpies of imidization reactions were determined and compared with the literature values. It is reported in literature³ that electron affinities of dianhydrides and ionization potentials of diamines, have strong influence on the reaction rate and activation energies of imidization. Activation energy (E_a) values were found to be 66 and 57 kJ/mol for DAPDS/PMDA and DAPDS/BTDA respectively, and order of reaction was found to be second order. Polyimides DAPDS/PMDA and DAPDS/BTDA, subjected to kinetic investigation, showed glass transition temperatures of 267°C and 241°C, both were found to be thermally stable up to 500°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2981–2990, 1997     

Kinetic behaviour of aluminum naphthenate/benzene system in process of gelation and degradation

The kinetic behaviour of aluminum naphthenate/benzene system in the process of gelation and degradation was systematically studied. The results obtained from the kinetic experiments indicated that the gelation stage was in accordance with a kinetic model of an auto-catalytic first-order reaction, and the degradation stage was a simple first-order reaction. The rate constants in these two stages at various temperaturs were measured. And the determined apparent activation energies for the gelation stage and for the degradation stage are 27.5±2.0 and 37.7±2.3 kJ/mol, respectively.     

样条函数逼近法研究环氧树脂固化动力学

采用样条函数逼近DSC曲线,分别对4,5-环氧环已烷1,2-二甲酸二缩水甘油酯、四氢邻苯二甲酸二缩水甘油酯及双酚A二缩水甘油醚与间苯二胺的固化动力学作了研究.结果表明,样条函数逼近DSC曲线有较高的精度,由模拟函数处理实验数据取得较满意的结果.     

Modeling stable free-radical polymerization

A kinetic model has been developed for stable free-radical polymerization (SFRP) processes by using the method of moments. This model predicts monomer conversion, number-average molecular weight, and polydispersity of molecular weight distribution. The effects of the concentrations of initiator, stable radical, and monomer, as well as the rate constants of initiation, propagation, termination, transfer, and the equilibrium constant between active and dormant species, are systematically investigated by using this model. It is shown that the ideal living-radical polymerization having a linear relationship between number-average molecular weight and conversion and a polydispersity close to unity is the result of fast initiation, slow propagation, absence of radical termination, and a high level of dormant species. Increasing stable radical concentration helps to reduce polydispersity but also decreases polymerization rate. Thermal initiation significantly broadens molecular weight distribution. Without the formation of dormant species, the model predicts a conventional free-radical polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2692–2704, 1999     

Cure kinetics of biphenyl epoxy‐phenol novolac resin system using triphenylphosphine as catalyst

The effects of the concentration of triphenylphosphine as a catalyst on the cure reaction of the biphenyl epoxy/phenol novolac resin system were studied. The kinetic study was carried out by means of the analysis of isothermal experiments using a differential scanning calorimeter. All kinetic parameters including the reaction orders, activation energy and kinetic rate constants were evaluated. To describe the cure reaction with the catalyst concentration, the normalized kinetic model was developed. The suggested kinetic model with a diffusion term was successfully able to describe and predict the cure reaction of epoxy resin compositions as functions of the catalyst content and temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 713–720, 1999     

Deep oxidation of methane on granulated and monolith copper—manganese oxide catalysts

Deep oxidation of methane on the granulated Cu—Mn-mixed oxide catalyst and metallic monolith catalysts coated with the same oxide was studied. The experimental kinetic curves for both monolith and granulated catalysts are satisfactorily described by the first-order rate law. The values of activation energies, reaction rate constants, and feed flow rates for the specified conversion almost coincide for both types of the catalysts. The data obtained confirm the possibility of a quantitative comparison of the activities of the granulated and monolith catalysts. The activity of the monoliths is proportional to the concentration of the active component.     

Liquid‐phase polymerization of propylene with a highly active Ziegler–Natta catalyst. Influence of hydrogen,cocatalyst, and electron donor on the reaction kinetics

This paper presents an experimental kinetic study of the polymerization of propylene in liquid monomer with a high activity catalyst. The influences of the concentration of hydrogen and the molar ratios of the catalyst, cocatalyst, and electron donor on the activation period, the maximum activity, the yield, and the decay behavior have been investigated at a temperature of 42°C using a relatively simple kinetic model. On the basis of the experimental data, the reaction rate has been modeled as a function of the hydrogen concentration, the molar ratio of cocatalyst and titanium, and the molar ratio of the electron donor and the cocatalyst. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 219–232, 1999     

Derivatographic investigations of polycarbonates

Derivatographic non-isothermal investigations of the decomposition of PC in air provide useful information on the characteristic decomposition temperatures and the apparent activation energies of the observed steps of decomposition. The following sequence of apparent activation energies of the pyrolysis step was obtained: PC-M>PC-C>PC-A. The values ofE for PC-M are the highest, due to shielding of the ester linkages by the ortho-methyl substituents.This work was supported by a grant from the National Scientific research Committee.     

Tentative explanation for the kinetic compensation effect in doped catalysts

The kinetic parameter compensation effect displayed by heterogeneous catalysts may occur when the global reaction is a combination of competing reactions which show the same mechanism and take place on different groups of active centres, each group showing different activation energy and pre-exponential factor values. In this study, a simple procedure is described for employing apparent kinetic data (lnA and E _a) that show a compensation effect in order to calculate the activation energies and pre-exponential factors (proportional to the population densities) of active centres that present equal reaction mechanisms in dual site catalysts. The procedure was used to reproduce apparent kinetic data taken from the literature and obtained from experiments with doped-catalysts prone to dual-site catalytic behaviour. The fittings obtained in all cases were very good. The population density of active centres with $E_{a_2 }$ activation energy showed constant growth with the increase in doping agent content, whereas that of the active centres originally present in the undoped catalysts $\left( {E_{a_1 } } \right)$ showed varying trends.     

Curing kinetics of arylamine-based polyfunctional benzoxazine resins by dynamic differential scanning calorimetry

In this study, the curing kinetics of polyfunctional benzoxazine resins based on arylamine, i.e. aniline and 3,5-xylidine, designated as BA-a and BA-35x, respectively, were investigated. Non-isothermal differential scanning calorimetry (DSC) at different heating rates is used to determine the kinetic parameters and the kinetic models of the curing processes of the arylamine-based polyfunctional benzoxazine resins were proposed. Kissinger, Ozawa, Friedman, and Flynn-Wall-Ozawa methods were utilized to determine the kinetic parameters of the curing reaction. BA-a resin shows only one dominant autocatalytic curing process with the average activation energy of 81-85 kJ mol⁻¹, whereas BA-35x exhibits two dominant curing processes signified by the clear split of the curing exotherms. The average activation energies of low-temperature curing (reaction (1)) and high-temperature curing (reaction (2)) were found to be 81-87 and 111-113 kJ mol⁻¹, respectively. The reaction (1) is found to be autocatalytic in nature, while the reaction (2) exhibits nth-order curing kinetics. In addition, the predicted curves from our kinetic models fit well with the non-isothermal DSC thermogram.     

Single‐pulse pulsed laser polymerization–electron paramagnetic resonance investigations into the termination kinetics of n‐butyl acrylate macromonomers

The termination of model mid‐chain radicals (MCRs), which mimic radicals that occur in acrylate polymerization over a broad range of reaction conditions, has been studied by single‐pulse pulsed laser polymerization (SP‐PLP) in conjunction with electron paramagnetic resonance spectroscopy. The model radicals were generated by initiator‐fragment addition to acrylic macromonomers that were preformed prior to the kinetic experiments, thus enabling separation of termination from the propagation reaction, for these model radicals propagate sparingly, if at all, on the timescale of SP‐PLP experiments. Termination rate coefficients of the MCRs were determined in the temperature range of 0–60°C in acetonitrile and butyl propionate solution as well as in bulk macromonomer over the range of 0–100 °C. Termination rate coefficients slightly below those of the corresponding secondary radicals were deduced, demonstrating the relatively high termination activity of this species, even when undergoing MCR–MCR termination. For chain length of 10, a reduction by a factor of 6 is observed. Unusually high activation energies were found for the termination rate coefficient in these systems, with 35 kJ mol^?1 being determined for bulk macromonomer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Examining the kinetics of the thermal polymerization of commercial aromatic bis‐benzoxazines

Three commercial bis‐benzoxazine monomers based on the aniline derivatives of bisphenol A (BA‐a), bisphenol F (BF‐a), and 3,3′‐thiodiphenol (BT‐a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The kinetics of the polymerization of BA‐a were found to be well described using an autocatalytic model for which values of n = 1.39 and m = 2.49 were obtained for the early and later stages of reaction respectively (activation energy = 81–88 kJ/mol.). Following recrystallization the same monomer yielded values of n = 1.80, m = 0.92, and E_a = 94–97 kJ/mol. BF‐a and BT‐a were also found to be well described using an autocatalytic model for which values of n = m = 2.11 (BF‐a) and n = 2.10, m = 1.47 (BT‐a) were obtained for the early and later stages of reaction (activation energy = 80–84 kJ/mol. for BF‐a and 88–95 kJ/mol. for BT‐a). The kinetic data are compared with parallel studies involving chemically initiated benzoxazine monomers. Molecular simulation is used to examine the rotational freedom of the central bridging units and this is related to the degree of conversion achieved. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2068–2081     

TBBPAER/DDM的固化反应动力学

用等温差示扫描量热法研究了4，4’-二氨基二苯甲烷固化四溴双酚-A环氧树脂的反应动力学，测定了固化反应热，得出了不同温度下固化反应速率与反应程度、固化反应程度与反应时间的关系曲线．结果表明等温固化反应按自催化反应机理进行，用Kamal方程较好地描述了不同温度下其固化反应的自催化反应过程，并反映出不同温度下扩散作用的差别，其动力学参数k1、k2、m、n由非线性回归法拟合而出，k1、k2对应的反应表现活化能分别为52．2kJ·mol-1和46．5kJ·mol-1。     

Determining the Reaction Mechanisms of Photo-Thermo Synergetic Processes by Kinetic Investigations

Photo-thermo catalysis utilizing light has been a promising strategy to improve the conventional thermal catalytic activity and attracts great attention nowadays. However, how heat works in synergy with light radiation is still unclear. This Concept article is trying to clarify the specific contents via summarizing the kinetic studies including 1) proposing elementary steps through pressure dependence studies, 2) estimating reaction barriers through measuring the apparent activation energies and 3) assigning the kinetically relevant step(s) with kinetic isotope effects (KIE) as well as 4) exploring the relationship of the reaction rate with the light excitation wavelength and light intensity. The challenges in kinetic studies such as describing the light-induced carrier transfer process, the surface temperature under light illumination as well as reaction intermediates were discussed at the same time. Finally, an outlook about kinetic studies in clarifying the photo-thermo catalysis reaction mechanism was proposed.     

The effect of ligand on the rate of propagation of Cu(0)‐wire catalyzed SET‐LRP of MA in DMSO at 25 °C

The effect of initial ligand concentration on the apparent rate constant of propagation of single‐electron transfer living radical polymerization (SET‐LRP) of MA in DMSO at 25 °C was examined using various lengths of Cu(0) wire as catalyst. It was determined that unlike other parameters such as initiator concentration, solvent concentration, and deactivator concentration, no simple external rate‐order for the ligand concentration could be determined. Rather, the response of the rate of SET‐LRP to initial ligand concentration is complex and is likely determined by a competition of ligand‐dependent extent of disproportionation as well as the role of ligand concentration in the surface mediated activation process. Results suggest that a minimum concentration of ligand is needed to achieve both acceptable reaction rate and reaction control, and therefore, ligand concentration must be considered in designing experimental conditions for SET‐LRP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5629–5638, 2009     

A comparative computational study of the homolytic and heterolytic bond dissociation energies involved in the activation step of ATRP and SET‐LRP of vinyl monomers

A quantum‐chemical calculation of the homolytic and heterolytic bond dissociation energies of the model compounds of the monomer and dimer is reported. These model compounds include the dormant chloride, bromide, and iodide species for representative activated and nonactivated monomers containing electron‐withdrawing groups as well as for a nonactivated monomer containing an electron‐donor group. Two examples of sulfonyl and N‐halide initiators are also reported. The homolytic inner‐sphere electron‐transfer bond dissociation is known as atom transfer and is responsible for the activation step in ATRP. The heterolytic outer sphere single electron transfer bond dissociation is responsible for the activation step in single electron transfer mediated living radical polymerization (SET‐LRP). The results of this study demonstrated much lower bond dissociation energies for the outer sphere single electron transfer processes. These results explain the higher rate constant of activation, the higher apparent rate constant of propagation, and the lower polymerization temperature for both activated and nonactivated monomers containing electron‐withdrawing groups in SET‐LRP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1607–1618, 2007