A kinetic study on the autocatalytic cure reaction of a cyanate ester resin

The cure of a novolac‐type cyanate ester monomer, which reacts to form a polycyanurate network, was investigated by using differential scanning calorimeter. The conversions and the rates of cure were determined from the exothermic curves at several isothermal temperatures (513–553 K). The experimental data, showing an autocatalytic behavior, conforms to the kinetic model proposed by Kamal, which includes two reaction orders, m and n, and two rate constants, k₁ and k₂. These kinetic parameters for each curing temperature were obtained by using Kenny's graphic‐analytical technique. The overall reaction order was about 1.99 (m = 0.99, n = 1.0) and the activation energies for the rate constants, k₁ and k₂, were 80.9 and 82.3 kJ/mol, respectively. The results show that the autocatalytic model predicted the curing kinetics very well at high curing temperatures. However, at low curing temperatures, deviation from experimental data was observed after gelation occurred. The kinetic model was, therefore, modified to predict the cure kinetics over the whole range of conversion. After modification, the overall reaction order slightly decreased to be 1.94 (m = 0.95, n = 0.99), and the activation energies for the rate constants, k₁ and k₂, were found to be 86.4 and 80.2 kJ/mol. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3067–3079, 2004     

Curing kinetics and thermal property characterization of a bisphenol‐S epoxy resin and DDS system

The kinetics of the cure reaction for a system of bisphenol‐S epoxy resin (BPSER), with 4,4′‐diaminodiphenyl sulfone (DDS) as a curing agent was investigated with a differential scanning calorimeter (DSC). Autocatalytic behaviour was observed in the first stages of the cure which can well be described by the model proposed by Kamal, using two rate constants, k₁ and k₂, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2∼2.5, and the activation energy for k₁ and k₂ was 86.26 and 65.13 kJ mol⁻¹, respectively. In the later stages, a crosslinked network was formed and diffusion control was incorporated to describe the cure. The glass transition temperature (T_g) of the BPSER/DDS samples partially cured isothermally was determined by means of torsional braid analysis (TBA) and the results showed that the reaction rate increased with increasing T_g, in terms of rate constant, but decreased with increasing conversion. It was also found that the  SO₂ group both in the epoxy resin and in the hardener increases the T_g values of the cured materials compared with that of BPAER. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of BPSER/DDS has nth order reaction kinetics. © 2000 Society of Chemical Industry     

Curing kinetics and thermal property characterization of the bisphenol‐F epoxy resin and phthalic anhydride system

The curing kinetics of bisphenol‐F epoxy resin (BPFER) and curing agent phthalic anhydride, with N,N‐dimethylbenzylamine as an accelerator, were studied by differential scanning calorimetry (DSC). Analysis of DSC data indicated autocatalytic behaviour in the first stages of the cure for the system, and that this, could be well described by the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The curing reaction in the later stages was practically diffusion‐controlled. To consider the diffusion effect more precisely, a diffusion factor, ??(α), was introduced into Kamal's equation. The glass transition temperatures (T_gs) of the BPFER/phthalic anhydride samples were determined by means of torsional braid analysis. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis. © 2002 Society of Chemical Industry     

Curing kinetics,thermal property,and stability of tetrabromo-bisphenol-A epoxy resin with 4,4′-diaminodiphenyl ether

The curing reaction of tetrabromo-bisphenol-A epoxy resin (TBBPAER) with 4,4′-diaminodiphenyl ether (DDE) was studied by isothermal differential scanning calorimetry (DSC) in the temperature range of 110–140°C. The results show that the isothermal cure reaction of TBBPAER–DDE in the kinetic control stage is autocatalytic in nature and does not follow simple nth-order kinetics. The autocatalytic behavior was well described by the Kamal equation. Kinetic parameters, including 2 rate constants, k₁ and k₂, and 2 reaction orders, m and n, were derived. The activation energies for these rate constants were 83.32 and 37.07 kJ/mol, respectively. The sum of the reaction orders is around 3. The glass transition temperatures (T_gs) were measured for the TBBPAER–DDE samples cured partially in isothermal temperature. With the degree of cure varies, different glass transition behaviors were observed. By monitoring the variation in these T_gs, it is illustrated that the network of the system is formed via different stages according to the sequence reactions of primary and second amines with epoxides. It is due to the presence of the 4 bromine atoms in the structure of TBBPAER that this curing process can be clearly observed in DSC curves. The thermal stability of this system studied by differential thermal analysis–thermogravimetric analysis illustrates that the TBBPAER–DDE material can automatically debrominate and takes the effect of flame retarding when the temperature reaches 238.5°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1991–2000, 1998     

CURING KINETICS AND THERMAL PROPERTY CHARACTERIZATION OF BISPHENOL-F EPOXY RESIN AND DDS SYSTEM

The curing kinetics of bisphenol-F epoxy resin (BPFER)/4,4′-diaminodiphenyl sulfone (DDS) system were studied by isothermal experiments using a differential scanning calorimeter (DSC). Autocatalytic behavior was shown in the first stages of the cure for the system, which could be well described by the model proposed by Kamal that includes two rate constants, k ₁ and k ₂, and two reaction orders, m and n. The curing reaction at the later stages was practically diffusion-controlled due to the onset of gelation and vitrification. To consider the diffusion effect more precisely, diffusion factor, f(α), was introduced into Kamal's equation. Thus, the curing kinetics could be predicted well over the whole range of conversion covering both pre- and postvitrification stages. The glass transition temperatures (T_gs) of the BPFER/DDS system isothermally cured partially were determined by means of torsional braid analysis (TBA), and the results showed that T_gs increased with conversion up to a constant value. The highest T_g was 406.2 K. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis (TGA), revealing two decomposition steps.     

Curing kinetics and thermal property characterization of an o‐cresol formaldehyde epoxy resin and 4,4′‐diaminodiphenyl ether system

The kinetics of the curing reaction for a system of o‐cresol formaldehyde epoxy resin (o‐CFER) with 4,4′‐diaminodiphenyl ether (DDE) as a curing agent were investigated with differential scanning calorimetry (DSC). An analysis of the DSC data indicated that an autocatalytic behavior appeared in the first stages of the cure for the system, and this could be well described by the model proposed by Kamal, which includes two rate constants and two reaction orders (m and n). The overall reaction order (m + n) was 2.7–3.1, and the activation energies were 66.79 and 49.29 kJ mol^?1, respectively. In the later stages, a crosslinked network was formed, and the reaction was mainly controlled by diffusion. For a more precise consideration of the diffusion effect, a diffusion factor was added to Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversions, covering both the previtrification and postvitrification stages. The glass‐transition temperatures of the o‐CFER/DDE samples were determined via torsional braid analysis. The results showed that the glass‐transition temperatures increased with the curing temperature and conversion up to a constant value of approximately 370 K. The thermal degradation kinetics of the system were investigated with thermogravimetric analysis, which revealed two decomposition steps. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 182–188, 2004     

Nonisothermal cure of bisphenol epoxy resin with a nonlinear aliphatic polyamine hardener

The amino terminated polypropylenimine dendrimer (DAB‐dendri‐(NH₂)₄) was employed as a new nonlinear aliphatic curing agent for diglycidyl ether of bisphenol A (DGEBA). Nonisothermal curing reaction kinetics of DGEBA/DAB was investigated with a differential scanning calorimeter (DSC). The apparent reaction activation energy E_a is about 56.7 kJ/mol determined using the Kissinger equation, and a two‐parameter (m, n) autocatalytic model ([icirc]Sesták–Berggren equation) was confirmed to be able to well simulate the reaction kinetics in the light of the Málek method. In addition, the relation between reaction activation energy E_a and curing degree α was obtained by applying model‐free isoconversional analysis with the Kissinger‐Akahira‐Sunose (KAS) method. As α increases, E_a reduced quickly from >80 kJ/mol to ≈60 kJ/mol up to a ≈ 15%, then decreased slowly to 55 kJ/mol till a ～ 75%, and finally dropped to 44 kJ/mol at full conversion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cure characterization of triglycidyl epoxy/aromatic amine systems

The curing of triglycidyl para-aminophenol (TGPAP) epoxy resin with three aromatic amine hardeners, diaminodiphenye sulphone (DDS), pyridinediamine (PDA), and toluenediamine (TDA), has been investigated. A series of iosthermal cures was conducted and analyzed by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). The chemical reactions occurring during cure were monitored at different temperatures by qualitative and quantitative estimation of different groups in the IR spectra, and the ratio of rate constants (k₂/k₁) were evaluated. Dynamic DSC analysis of TGPAP/TDA resulted in two exothermal peaks, indicating cure kinetics different from those of TGPAP/DDS and TGPAP/PDA systems, which gave a single exothermal peak. Various kinetic parameters such as total heat of reaction. ΔH′, activation energy E_a, Frequency factor z, and order of reaction n were evaluated for all the three systems. From the initial kick-off temperatures and activation energy values it was concluded that the rate of curing followed the order TDA > PDA > DDS. The reaction conversions during cure, evaluated from IR analysis, were exactly the same as those obtained from DSC Borchardt–Daniels kinetics. Using this model, the plots of time vs. temperature for different conversions were constructed for all the three systems; on the basis of these, the cure cycles can be fixed. © 1995 John Wiley & Sons, Inc.     

Curing Kinetics and Thermal Properties Characterization of o-Cresol-formaldehyde Epoxy Resin and MeTHPA System

The kinetics of the cure reaction for a system of o-cresol-formaldehyde epoxy resin (o-CFER) with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent and N,N-dimethyl-benzylamine as an accelerator was investigated by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure for the system, which could be well described by the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The activation energy E₁ and E₂ are 195.84 and 116.54 kJmol^?1, respectively. In the later stages, the reaction is mainly controlled by diffusion, and a diffusion, factor, f(α), was introduced into Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversion. Molecular mechanism for the curing reaction was discussed. The glass transition temperature T_g was determined by means of torsional braid analysis (TBA). The results showed that T_gs increased with curing temperature and conversion up to a constant value about 367.1 K. The thermal degradation kinetics of the system was investigated by thermogravimetric analysis (TGA), which revealed two decomposition steps.     

Reaction kinetics and physical properties of unsaturated polyester modified with methylacyloxylpropyl-POSS

The polyhedral oligomeric silsesquioxanes which contains methylacryloylpropyl group (MAP-POSS) was synthesized and used to modify unsaturated polyester resin (UPR). The cure kinetics was investigated by isothermal DSC technique. The mechanical and electrical properties of fiberglass-reinforced laminate were determined. The result shows that the reaction can be described by a Kamal autocatalytic model which has two reaction rate constants k ₁ and k ₂, and two apparent activation energies E _a1 and E _{a 2} are 98.12 kJ/mol and 74.01 kJ/mol, respectively. UPR and MAP-POSS can co-cure in free radical polymerization. When the MAP-POSS content is 5 wt%, the impact and tensile strength of fiberglass-reinforced laminate enhanced 10% and 6%, respectively, and has better electrical properties than no MAP-POSS. The dielectric constant ε and dielectric loss tanδ are all decrease. The surface resistance ρ _s is 4.7 times higher than pure UPR laminates     

Kinetics of aryl phosphinate anhydride curing of epoxy resins using differential scanning calorimetry

The curing reaction of two kinds of epoxy resins, (bisphenol A epoxy DER331, and novolac epoxy DEN438) with aryl phosphinate anhydride (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide)-methyl succinic anhydride (DMSA), and benzyldimethylamine (BDMA) as the catalyst, was investigated by differential scanning calorimetry (DSC) using an isothermal approach over the temperature range 130–160°C. The experimental results showing autocatalytic behaviour were compared with the model proposed by Kamal, including two rate constants (k₁ and k₂) and two reaction orders (m and n). The model predictions are in good agreement with the experimental data and demonstrate that the autocatalytic model is capable of predicting the curing kinetics of both systems without any additional assumptions. The activation energies for the rate constants of DER331/DMSA and DEN438/DMSA are 77–92 kJmol^-1 and 83–146 kJmol^-1, respectively. The obtained overall reaction order of 2 is in agreement with the reaction mechanism reported by several workers. © 1998 SCI.     

Curing kinetics and thermal property characterization of a bisphenol‐F epoxy resin and DDO system

The curing kinetics of a bisphenol‐F epoxy resin (BPFER)/4,4′‐diaminodiphenyl oxide (DDO) system were studied with isothermal experiments via differential scanning calorimetry. Autocatalytic behavior was shown in the first stages of the cure for the system, which was well described by the model proposed by Kamal that includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The curing reaction at the later stages was practically diffusion‐controlled because of the onset of gelation and vitrification. For a more precise consideration of the diffusion effect, a diffusion factor, f(α), was introduced into Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversion, covering both previtrification and postvitrification stages. The glass‐transition temperatures (T_g's) of the BPFER/DDO system partially isothermally cured were determined by means of torsional braid analysis, and the results showed that T_g's increased with conversion up to a constant value. The highest T_g was 376.3 K. The thermal degradation kinetics of cured BPFER were investigated with thermogravimetric analysis, which revealed two decomposition steps. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1586–1595, 2002     

双酚-S环氧树脂与间苯二胺固化反应动力学

用示差扫描量热法(DSC)研究了双酚-S环氧树脂(BPSER)与间苯二胺固化反应的历程。实验结果表明,固化反应主要分为2个阶段,前期由化学动力学控制,服从自催化机理,实验数据利用Kamal方程处理得到2个速率常数k1、k2及2个反应级数m、n,k1、k1值随反应温度的升高均呈增大的趋势,总反应级数m+n在2～2 5之间;反应活化能E1、E2分别为64 18kJ/mol和48 30kJ/mol。当反应程度达到60%左右后,由于交联程度增加,分子质量迅速增大,分子间扩散较慢,进入反应的第二阶段,主要由扩散作用控制固化速率。文章还讨论了该体系固化反应的分子机理,认为其经历了三分子的过渡态。     

Cure behavior of epoxy/MWCNT nanocomposites: The effect of nanotube surface modification

The effect of carboxyl and fluorine modified multi-wall carbon nanotubes (MWCNTs) on the curing behavior of diglycidyl ether of bisphenol A (DGEBA) epoxy resin was studied using differential scanning calorimetry (DSC), rheology and infrared spectroscopy (IR). Activation energy (E_a) and rate constants (k) obtained from isothermal DSC were the same for the neat resin and fluorinated MWCNT system (47.7 and 47.5 kJ/mol, respectively) whereas samples containing carboxylated MWCNTs exhibited a higher activation energy (61.7 kJ/mol) and lower rate constant. Comparison of the activation energies, rate constants, gelation behavior and vitrification times for all of the samples suggests that the cure mechanisms of the neat resin and fluorinated sample are similar but different from the carboxylated sample. This can be explained by the difference in how the fluorinated nanotubes react with the epoxy resin compared to the carboxylated nanotubes. Although the two systems have different reaction mechanisms, both systems have similar degrees of conversion as calculated from the infrared spectroscopic data, glass transition temperature (T_g), and predictions based on DSC data. This difference in reaction mechanism may be attributed to differences in nanotube dispersion; the fluorinated MWCNT system is more uniformly dispersed in the matrix whereas the more heterogeneously dispersed carboxylated MWCNTs can hinder mobility of the reactive species and disrupt the reaction stoichiometry on the local scale.     

Competitive primary amine/epoxy and secondary amine/epoxy reactions: Effect on the isothermal time-to-vitrify

The effect of temperature on the ratio of the kinetic rate constants, k₂/k₁, has been investigated using FTIR spectroscopy for the competing reactions of epoxy with secondary amine (k₂) and primary amine groups (k₁) in a trimethylene glycol di-p-aminobenzoate/diglycidyl ether of the bisphenol A system. The ratio of the rate constants increases from 0.16 to 0.33 in the temperature range 100?160°C. The corresponding difference in the activation energies for the competing reactions is about 3.7 kcal/mol. The effect of the ratio on the time-to-vitrify contour of the isothermal time–temperature–transformation (TTT) cure diagram is discussed: The effect is more significant at higher curing temperatures.     

Cure kinetics of ternary blends of epoxy resins studied by nonisothermal DSC data

The curing kinetics of blends of diglycidyl ether of bisphenol A (DGEBA), cycloaliphatic epoxy resins, and carboxyl‐terminated butadiene‐acrylonitrile random copolymer (CTBN) in presence of 4,4′‐diamino diphenyl sulfone (DDS) as the curing agent was studied by nonisothermal differential scanning calorimetry (DSC) technique at different heating rates. The kinetic parameters of the curing process were determined by isoconversional method given by Malek for the kinetic analysis of the data obtained by the thermal treatment. A two‐parameter (m, n) autocatalytic model (Sestak‐Berggren equation) was found to be the most adequate selected to describe the cure kinetics of the studied epoxy resins. The values of E_a were found to be 88.6 kJ mol^?1 and 61.6 kJ mol^?1, respectively, for the studied two sample series. Nonisothermal DSC curves obtained using the experimental data show a good agreement with that theoretically calculated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Kinetics and thermal properties of epoxy resin cured with Ni(II)‐tris‐(O‐pheneylendiamine) bromide

Diglycidyl ether of bisphenol A (DGEBA) is cured with a nickel complex of O‐phenylendiamine (OPD) as a ligand. The structure of the synthesized curing agent is confirmed through IR and elemental analysis. The curing kinetics of DGEBA/Ni(OPD)₃Br₂ system is studied by the dynamic DSC and isothermal FTIR techniques. In all cases, we have observed at least two exothermic peaks during DSC traces up to 350°C. Dynamic activation energies are calculated by using the two isoconversional, Kissinger and Ozawa, methods applied to peak maximum. A two‐parameter (m, n) autocatalytic model (Sestak–Berggren equation) is found to be the most adequate model to describe the cure kinetics of the observed thermal events. Isothermal kinetic parameters are estimated using the Horie model. The onset decomposition temperature and char yield (at 700°C) of the crosslinked material were 290°C and 27%, respectively. The activation energy of the solid‐state thermal degradation process is evaluated by Ozawa approach, resulting in 95–138 kJ/mol on a range of 2–20% decomposition conversion. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1257–1265, 2006     

The kinetic study of the curing reaction of mono- and di-epoxides obtained during the reaction of divinylbenzene and hydrogen peroxide with acid anhydrides

In this paper, the non-isothermal differential scanning calorimetry (DSC) was employed to investigate the cure process and to determine the kinetic parameters of the curing reactions of mono- and di-epoxides with maleic and glutaric anhydrides. The epoxides were obtained during the epoxidation process of commercially available divinylbenzene by using 60% hydrogen peroxide as the oxidant in the presence of organic solvents and magnesium oxide as the catalyst. It was found that the cure process of epoxides with maleic anhydride was described through higher values of enthalpy of polymerization (ΔH_R) and lower temperatures of the cure initiation (T_onset), the peak maximum temperature (T_max) and the final cure temperature (T_end). It can be considered to accelerate the rate of reaction and lead to an excellent network structure when maleic anhydride was used as curing agent. The kinetic analysis was firstly computed using a model free-estimation of the activation energy (Friedman, Ozawa-Flynn-Wall methods) and then the multivariate non-linear regression with a 6th degree Runge-Kutta process in a modified Marquardt procedure was employed to calculate the corresponding kinetic parameters (E_i, n_i, A_i) using the nth-order reaction f(α). The unbranched three-step process of the nth-order reaction f(α) for each step was the best to describe the cure process of mono- and di-epoxide with acid anhydrides. The determined values of the activation energies were in the range 64.7-105.2 kJ/mol for epoxides/glutaric anhydride system and 64.7-82.7 kJ/mol when maleic anhydride was used as hardening agent.