DSC curing study of catalytically synthesized maleic‐acid‐based unsaturated polyesters

Unsaturated polyesters were synthesized based on ethylene glycol and maleic acid as unsaturated dicarboxylic acid, using a variety of saturated acids in the initial acid mixture, without or with different catalysts. The curing of the polyesters produced with styrene was studied using differential scanning calorimetry (DSC) under dynamic‐ and isothermal‐heating conditions. The FTIR spectra of the initial polyesters and cured polyesters were also determined. Curing is not complete at the end of DSC scan and the unreacted bonds were quantitatively determined from the FTIR spectra and by estimation based on literature data. The value of the mean degree of conversion (α) of all double bonds (styrene unit and maleate unit) was approximately α = 0.40. Using an appropriate kinetic model for the curing exotherm of polyesters, the activation energy (E_a), the reaction order (x) and the frequency factor (k_o) were determined. Because the kinetic parameters (ie E_a, k, x) affect the kinetics in various different ways, the curves of degree of conversion versus time at various isothermal conditions are more useful to compare and characterize the curing of polyesters. The kinetic parameters are mainly influenced by the proportion of maleic acid in the polyesterification reaction mixture and secondarily by the residual polyesterification catalyst. The degree of conversion of already crosslinked polyesters is greatly increased by post‐curing them at elevated temperature and for a prolonged time. © 2002 Society of Chemical Industry     

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     

The research on syntheses and properties of novel epoxy/polymercaptan curing optical resins with high refractive indices

A novel thioether glycidyl resin bis[3-(2,3-Epoxypropylthio)phenyl]-sulfone (BEPTPhS) with high refractive index was synthesized by condensation of bis(3-mercaptophenyl)sulfone (BMPS) with epichlorohydrin. It's structure was characterized by FTIR, MS and NMR. It was the first time that trimercaptothioethylamine (TMTEA) was used as curing agent to cure epoxy resins. Optical resins possessing high refractive index were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with the mixture of TMTEA and ethylendiamine (EDA) and by curing BEPTPhS/DGEBA with TMTEA. The research on the optical properties of resins of DGEBA cured by the mixtures of TMTEA and EDA indicated that these resins possess higher refractive index (n_d>1.60), lower dispersity (ν_d>34), high impact strength (IPS>30 kJ m⁻²) and higher transmittance. The n_d, ν_d and density of these resins varied linearly with the EDA content in the curing agent mixtures. The optimum ratio of the EDA content to that of TMTEA is 20:80 (molar ratio), at this ratio the cured resin has the optimum optical properties (n_d²⁰=1.61, v_d=35.4). The cured resins of BEPTPhS/TMTEA have a high refractive index (the highest is n_d=1.67). The optical, physical and thermal properties of the cured optical resins of BEPTPhS/TMTEA were discussed in this paper.     

Kinetics and thermodynamics of isothermal curing reaction of epoxy‐4, 4′‐diaminoazobenzene reinforced with nanosilica and nanoclay particles

The kinetics of the cure reaction for a system of bisphenol‐A epoxy resin (DGEBA), with 4, 4′‐diaminoazobenzene (DAAB), reinforced with nanosilica (NS), and nanoclay (NC) by means of isothermal technique of differential scanning calorimetry were studied. The Kamal autocatalytic‐like kinetic model was used to estimate the reaction orders (m, n), rate constants (k₁, k₂), and also active energies (E_a) and pre‐exponential factors (A) of the curing reaction. However, the existence of NS and NC with hydroxyl groups in the structure improves the cure reaction and influence the rate of reaction and therefore kinetics parameters. The E_a of cure reaction of DGEBA/DAAB system showed a decrease when nanoparticles were present and therefore the rate of the reaction was increased. Using the rate constants from the kinetic analysis and transition state theory, thermodynamic parameters such as enthalpy (ΔH^#), entropy (ΔS^#), and Gibbs free energy (ΔG^#) changes were also calculated. The thermodynamic functions were shown to be very sensitive parameters for evaluation of the cure reaction. POLYM. COMPOS., 31:1442–1448, 2010. © 2009 Society of Plastics Engineers     

Moisture curing kinetics of isocyanate ended urethane quasi‐prepolymers monitored by IR spectroscopy and DSC

The study of the kinetics of the curing of isocyanate quasi‐prepolymers with water was performed by infrared spectroscopy and differential scanning calorimetry. The influence of the free isocyanate content, polyol functionality, and of the addition of an amine catalyst (2,2′‐dimorpholinediethylether) in the reaction kinetics and morphology of the final poly(urethane urea) was analyzed. A second‐order autocatalyzed model was successfully applied to reproduce the curing process under isothermal curing conditions, until gelation occurred. A kinetic model‐free approach was used to find the dependence of the effective activation energy (E_a) with the extent of cure, when the reaction was performed under nonisothermal conditions. The dependence of E_a with the reaction progress was different depending on the initial composition of the quasi‐prepolymer, which reveals the complexity of the curing process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Curing behavior of epoxy resins in two‐stage curing process by non‐isothermal differential scanning calorimetry kinetics method

In this research, a new thermal curing system, with two‐stage curing characteristics, has been designed. And the reaction behaviors of two different curing processes have been systematically studied. The non‐isothermal differential scanning calorimetry (DSC) test is used to discuss the curing reaction of two stages curing, and the data obtained from the curves are used to calculate the kinetic parameters. Kissinger‐Akahira‐Sunose (KAS) method is applied to determine activation energy (E_a) and investigate it as the change of conversion (α). Málek method is used to unravel the curing reaction mechanism. The results indicate that the curing behaviors of two different curing stages can be implemented successfully, and curing behavior is accorded with ?esták‐Berggren mode. The non‐isothermal DSC and Fourier transform infrared spectroscopy test results reveal that two different curing stages can be implemented successfully. Furthermore, the double x fitting method is used to determine the pre‐exponential factor (A), reaction order (m, n), and establish the kinetic equation. The fitting results between experiment curves and simulative curves prove that the kinetic equation can commendably describe the two different curing reaction processes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40711.     

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     

Studying the effect of micro- and nano-sized ZnO particles on the curing kinetic of epoxy/polyaminoamide system

The present study investigated curing kinetic of epoxy/polyaminoamide/ZnO implementing isothermal differential scanning calorimetry (DSC) technique. Model free and model fitting methods were used to study the curing reaction kinetic. Isoconversional method results showed that the activation energies (E_a) of pure epoxy/polyaminoamide, epoxy/polyaminoamide/micro-ZnO, and epoxy/polyaminoamide/nano-ZnO systems remained constant in different conversions. Moreover, the model fitting method was used to determine the kinetic triplet, i.e., pre-exponential factor [A], activation energy [E_a], and reaction order [n] by simultaneous processing of all isothermal curing data. Both methods indicated a decrease in activation energy by adding ZnO as well as a decrease in the particle size from micro to nanoscale. This can be attributed to the catalytic effect of ZnO by forming a complex between Zn⁺⁺ and oxygen of oxirane ring and carboxylate group in epoxy.     

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     

Kinetic rate equation combining ultraviolet‐induced curing and thermal curing. I. Bismaleimide system

A novel and general kinetic rate equation combining ultraviolet‐induced (UV‐induced) curing and thermal curing was successfully derived from the conventional thermal‐kinetic rate equation. This proposed novel kinetic rate equation can be applicable to the curing system either simultaneously or individually by UV‐induced and thermal cure methods. This general kinetic rate equation is composed of the reaction order n, activation energy E_a, curing temperature T, energy barrier of photoinitiation E_Q, intensity of UV radiation Q, concentration of photoinitiator [I], and a few other parameters. The proposed equation was supported by experimental data based on the curing systems of 4,4′‐bismaleimidodiphenylmethane (BMI) and 2,2‐bis(4‐(4 maleimido phenoxy) phenyl propane (BMIP). The BMI and BMIP systems were isothermally cured at various temperatures, or simultaneously cured with varying intensity of UV radiation (wavelength 365 nm). Conversion levels for the various cured samples were subsequently measured with a FTIR spectrometer. The reaction order n = 1.2, activation energy E_a = 40,800 J/mol, and E_Q = 7.5 mW/cm² were obtained for curing BMI system. The reaction order n = 1.3, activation energy E_a = 53,000 J/mol, and E_Q = 9.1 mW/cm² were obtained for curing BMIP system. The values of n and E_a in the same curing system (BMI or BMIP) are irrespective of the curing method (either simultaneously or individually by UV‐induced and thermal cure methods). The salient results of this study show that UV radiation only enhances the initiation rate and UV ration do not influence the activation energy E_a. The experimental results are reasonably well represented by these semi‐empirical expressions.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Kinetic study by FTIR,TMA, and DSC of the curing of a mixture of DGEBA resin and γ‐butyrolactone catalyzed by ytterbium triflate

A mixture of diglycidylether of bisphenol A (DGEBA) and γ‐butyrolactone (γ‐BL) was cured in the presence of ytterbium triflate as a catalyst. The kinetics of the various elemental processes that occur in the curing process were studied by means of isothermal curing in the FTIR spectrometer. The kinetics of the contraction during the curing was also evaluated by TMA. In both cases, the kinetics was analyzed by means of isoconversional procedure and the kinetic model was determined with the so‐called compensation effect (isokinetic relationship). The isothermal kinetic analysis was compared with that obtained by dynamic curing in DSC. We found that all the reactive processes and the contraction follow a surface‐controlled reaction type of kinetic mechanism, R₃. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 381–393, 2004     

Thermal scanning rheometric analysis of curing kinetic of an epoxy resin. I. An anhydride as curing agent

The curing reaction of the system diglycidyl ether of bisphenol A (DGEBA), an organic anhydride (HMTPA), as curing agent and a tertiary amine (DMP 30) as initiator has been studied by Thermal Scanning Rheometry (TSR) under isothermal conditions. The gel time, which is defined by several different criteria, has been found to be a good parameter to determine the activation energy of this curing process; on the other hand, the gel time depends on the concentration of the initiator. An empirical model has been used to predict the change in viscosity (η*) of the system with time until the gelation is reached; the first‐order kinetics, the apparent kinetic constant (k′), and the activation energy before gelation have been determined. Furthermore, these results are reported together with the reaction mechanism proposed by another authors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1239–1245, 1999     

Kinetics analysis of the curing reaction of fast cure epoxy prepregs

In this article, the curing kinetics of two fast cure flip-chip epoxy encapsulants under both isothermal and nonisothermal conditions are investigated by differential scanning calorimetry. The method allows determination of the most suitable kinetic model and corresponding parameters. The kinetic analysis suggests that the two-parameter autocatalytic model is more appropriate to describe the kinetics of the curing reaction. There are certain differences between the kinetic data from isothermal and that from nonisothermal measurements. The apparent activation energy Ea and pre-exponential factor A of E-AB1 determined from nonisothermal experiments were higher than the isothermal values, whereas the Ea and A of E-RV2 determined from both methods are relatively close. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1501–1508, 1999     

The kinetics of oxidation curing of polycarbosilane fibers

For the oxidation curing of polycarbosilane (PCS) fibers in air, a first-order reaction based on the weight gainw (in percentage) was approached with the kinetic equationdwldt=k(w _m-w). The maximum weight gain w_m was observed to be 16% under normal oxidation conditions and the activation energyE to be 79.27 kJ/mol. The numeric integration based on the kinetics provides a precise prediction of the curing degree of PCS fibers under various heating programs and conditions.     

Curing behavior and thermal property of epoxy resin with boron‐containing phenol‐formaldehyde resin

The curing reaction of bisphenol‐A epoxy resin (BPAER) with boron‐containing phenol–formaldehyde resin (BPFR) was studied by isothermal and dynamic differential scanning calorimetry (DSC). The kinetic reaction mechanism in the isothermal reaction of BPAER‐BPFR was shown to follow autocatalytic kinetics. The activation energy in the dynamic cure reaction was derived. The influence of the composition of BPAER and BPFR on the reaction was evaluated. In addition, the glass transition temperatures (T_gs) were measured for the BPAER‐BPFR samples cured partially at isothermal temperatures. With the curing conditions varying, different glass transition behaviors were observed. By monitoring the variation in these T_gs, the curing process and the thermal property of BPAER–BPFR are clearly illustrated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1054–1061, 2000     

Kinetics of 4,4′-diaminodiphenylmethane curing of bisphenol-S epoxy resin

The kinetics of the cure reaction for a system of bisphenol-S epoxy resin (BPSER), with 4,4′-diaminodiphenylmethane (DDM) as a curing agent, were studied by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure, with the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. Rate constants k₁ and k₂ were observed to be greater when curing temperature increased. The over-all reaction order, m + n, is in the range of 2.5 ∼ 3. The activation energies for k₁ and k₂ were 55 kJ/mol and 57 kJ/mol, respectively. Diffusion control is incorporated to describe the cure in the latter stages. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1799–1803, 1999     

Cure kinetics of the cardanyl acrylate–styrene system using isothermal differential scanning calorimetry

The curing kinetics of styrene (30 wt %) and cardanyl acrylate (70 wt %), which was synthesized from cardanol and acryloyl chloride, was investigated by differential scanning calorimetry under isothermal condition. The method allows determination of the most suitable kinetic model and corresponding parameters. All kinetic parameters including the reaction order, activation energy E_a and kinetic rate constant were evaluated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2034–2039, 2002