Effect of the crosslinking degree on curing kinetics of an epoxy–anhydride styrene copolymer system

The cure kinetics of a high molecular weight acid copolymer used as a hardener for a commercial epoxy resin (DGEBA) was studied by DSC. The systems were uncured and partially cured epoxy poly(maleic anhydride-alt-styrene) (PAMS) at different periods of time. The state of cure was assessed as the residual heat of reaction and was varied by controlling both the time and temperature of cure. The conversion degree of crosslinking increased with time and temperature. Additionally, the activation energy and reaction order were calculated by the Freeman–Carrol relation and showed a dependence on the conversion degree of crosslinking. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2089–2094, 1999     

Effect of the crosslinking degree on curing kinetics of an epoxy–acid copolymer system

The hardening of a commercial epoxy resin (DGEBA) with the cure of high molecular weight acid copolymers was studied using differential scanning calorimetry (DSC). The systems were uncured and partially cured epoxy/poly(acrylic acid–styrene) (SAAS), at different contents of styrene. The conversion degree of the crosslinking of the systems, examined versus time, temperature of hardening, and styrene contents in the copolymers, were determined. The activation energies of the crosslinking reactions were calculated by the Freeman–Carrol relation and showed a dependence on the state of hardening. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2834–2839, 2003     

The effect of bismaleimide resin on curing kinetics of epoxy–amine thermosets

An analysis of the cure kinetics of several formulations composed of diglycidyl ether of bisphenol-A (DGEBPA) and aromatic diamines, methylenedianiline (MDA) and diaminodiphenyl sulfone (DDS), in the absence and presence of 4,4′-bismaleimidodiphenylmethane (BM) was performed. The dynamic differential scanning calorimetry (DSC) thermograms were analyzed with the help of ASTM kinetic software to determine the kinetic parameters of the curing reactions, including the activation energy, preexponential factor, rate constant, and 60 min ½ life temperature. The effects of substitution of one curing agent for another, their concentration, and the absence and presence of BM resin and its concentration on curing behavior, ethalpy, and kinetic parameters are discussed. © 1996 John Wiley & Sons, Inc.     

A random acrylate copolymer with epoxy‐amphiphilic structure as an efficient toughener for an epoxy/anhydride system

Toughening of epoxy resin by block copolymers containing an epoxy‐philic block and an epoxy‐phobic block is usually costly because of their complex preparation procedure. In this work, a novel, random epoxy‐amphiphilic copolymer (PHGEL), which combines an “epoxy‐philic” component and an “epoxy‐phobic” component, has been synthesized and evaluated as a potential toughening agent for a diglycidyl ether of bisphenol A–based epoxy thermoset (EP). The curing behavior of the EP/PHGEL system has been investigated, and the results show that the hydroxyl group on the PHGEL chain can slightly activate the curing reaction. The mechanical testing shows that the toughness of the epoxy resin is improved by 294% when 4 wt % of PHGEL is added. Simultaneously, the tensile strength, elongation at break, and glass‐transition temperature are also improved. In addition, the thermogravimetric analysis shows that PHGEL has no obvious effect on the thermal stability of the epoxy thermosets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44863.     

New epoxy resins. I. The stability of epoxy–trialkoxyboroxines triaryloxyboroxine system

A polymer with high aromaticity and/or cyclic ring structures chain backbone usually has high heat, thermal, and flame resistance. Two diglycidyl ethers of bisphenols were prepared from 4,4′ isopropylidenediphenol (DGEBA) and 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) for evaluation. Four boroxines—trimethoxyboroxine (TMB), triethoxyboroxine (TEB), triisopropoxyboroxine (TIPB) and triphenoxyboroxine (TPB)—were used as the curing agents. DGEBA and DGEBF cured with various boroxines indicate that the trend for their respective glass transition temperature (T_g's), degradation temperatures (T_d's), and gel fractions are TMB-cured epoxy ≈ TEB-cured epoxy < TIPB cured epoxy < TPB cured epoxy. The DGEBF system usually has a higher T_g, T_d, gel fraction, oxygen index (OI), and char yield than the related DGEBA system. DGEBF/DGEBA (80/20 mol ratio) shows a synergistic effect in regard to char formation. This effect exists not only in the copolymer system but also in blended homopolymers of the separately cured resins. A modified mechanism for the polymerization of phenyl glycidyl ether (PGE) with TMB has been proposed.     

Curing kinetics and chemorheology of epoxy/anhydride system

The curing kinetics and chemorheology of a low‐viscosity laminating system, based on a bisphenol A epoxy resin, an anhydride curing agent, and a heterocyclic amine accelerator, are investigated. The curing kinetics are studied in both dynamic and isothermal conditions by means of differential scanning calorimetry. The steady shear and dynamic viscosity are measured throughout the epoxy/anhydride cure. The curing kinetics of the thermoset system is described by a modified Kamal kinetic model, accounting for the diffusion‐control effect. A chemorheological model that describes the system viscosity as a function of temperature and conversion is proposed. This model is a combination of the Williams–Landel–Ferry equation and a conversion term originally used by Castro and Macosko. A good agreement between the predicted and experimental results is obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3012–3019, 2003     

Glass‐transition temperature–conversion relationship for an epoxy–hexahydro‐4‐methylphthalic anhydride system

The DGEBA–MHHPA epoxy system has found increasing applications in microelectronics packaging, making crucial the ability to understand and model the cure kinetics mechanism accurately. The present article reports on work done to elucidate an appropriate model, modified from the empirical DiBenedetto's equation, to relate the glass‐transition temperature (T_g) to the degree of conversion for a DGEBA–MHHPA epoxy system. This model employs the ratio of segmental mobility for crosslinked and uncrosslinked polymers, λ, to fit the model curve to the data obtained. A higher ratio value was shown to indicate a more consistent rate of increase of T_g in relation to the degree of conversion, while a lower value indicated that the rate of T_g increase was disproportionately higher at higher degrees of conversion. The best fit value of λ determined by regression analysis for the DGEBA–MHHPA epoxy system was 0.64, which appeared to be higher than for those previously obtained for other epoxy systems, which ranged from 0.43–0.58. The highest T_g value obtained experimentally, T_{g max}, was 146°C, which is significantly below the derived theoretical maximum T_g∞ value of 170. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 511–516, 2000     

Determining the gel point of an epoxy–hexaanhydro‐4‐methylphthalic anhydride (MHHPA) system

The DEBGA–MHHPA epoxy system has found increasing applications in microelectronics packaging for which the ability to understand and model the cure kinetics mechanism accurately is crucial. The present article reports on the work done to elucidate accurate knowledge of the gel point by rheological methods. To determine the gel point using the G′–G″ crossover method was found not to be accurate, and the gel point obtained by this method was found to be frequency‐dependent. Using the point where tgδ was found independent of the frequency can accurately define the gel point at different temperatures. At the gel point determined by this method, G′ and G″ were found to follow the same power law, demonstrating the accuracy of the method in determining the gel point. The scaling exponent obtained was 0.75–0.79. The activation energy for the cure reaction of the system was determined to be 75.1 kJ/mol by the obtained gel times at different temperatures. The steady‐shear rheology test was also used to observe the viscosity change at the gel point. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1248–1256, 2000     

Viscoelastic changes of epoxy resin–acid anhydride system during curing

The changed viscoelastic properties of the epoxy resin-acid anhydride system, Epikote 834-HHPA, are followed to the gel point at 130, 140, and 150°C with a dynamic viscoelastometer. The viscosity increases with curing time through two inflections designated A and B. The point A is interpreted (from the reference to the chemical changes reported in the previous paper) as the termination of the initial stage of this curring reaction, and point B coincides with the gel point determined by the torsion method. The resonance frequency remains constant value up to the point B, followed by a rapid increase. The extents of reaction for epoxide, anhydride, and initial OH are 15, 45.8, and 100% at the point A; 27.8, 63.7, and 100% at the point B, respectively. The apparent activation energies for viscosity are 7.5 kcal/mole for the resin mixture before curing, 10.5 kcal/mole for point A, 48.8 kcal/mole for point B (gel point). The overall apparent activation energies of this curing reaction are obtained from the Arrhenius plots for the curing time required for the resin mixture to reach the state of the points A and B; these values were 8.9 kcal/mole for point A and 16.2 kcal/mole for point B.     

Use of temperature‐modulated DSC in kinetic analysis of a catalysed epoxy–anhydride system

The curing kinetics of a catalysed epoxy‐anhydride system was studied by temperature‐modulated differential scanning calorimetry. The chemical‐controlled regime was analysed by empirical kinetic equations. The diffusion‐controlled regime was detected by the diffusion factor, DF(α,T), which was calculated from the ratio of the experimental rate to the chemical reaction rate. DF(α,T) was compared with a mobility factor, MF(α,T), which was obtained by measuring the modulus of the complex heat capacity |C_p*|. The equivalence of the two factors allowed the diffusion‐controlled regime to be studied using the |C_p*| signal. However, the results obtained in the epoxy–anhydride system showed a limitation to the method, and this is discussed in terms of the modulation period necessary for the variation in MF(α,T) to occur in the same conversion interval as does DF(α,T). Copyright © 2004 Society of Chemical Industry     

Bulk properties of epoxy resin modified by epoxy–aminosilane copolymers

A linear epoxy–aminopropyltriethoxysilane addition polymer was used as a new epoxy modifier. In this paper, the thermal and mechanical properties have been determined by differential scanning calorimetry (DSC) and mechanical testing. The experimental results show that this copolymer modifier can effectively improve the toughness of resins without sacrificing their thermal resistance, stiffness and strength. As a comparison, the properties of epoxy resin blended with aminopropyltriethoxysilane (γ-APS) have been carried out simultaneously. © 1999 Society of Chemical Industry     

Cure kinetics of a low epoxide/hydroxyl group-ratio bisphenol a epoxy resin–anhydride system by infrared absorption spectroscopy

An infrared absorption spectroscopy study of the curing kinetics of a low (1.12) epoxide/hydroxyl-group ratio bisphenol A epoxy resin—phthalic anhydride system is reported. A full infrared peak assignment to molecular vibrational modes is given for the range 400 to 4000 cm^?1, and the optical density behavior of all peaks during reaction is discussed in detail. Proposed rival reaction mechanisms are considered and their respective kinetic behavior discussed. The reaction was found to follow consecutive-step addition esterification and simultaneous addition etherification, and epoxide—hydroxyl group and carboxylic acid dimer hydrogen bonding was found to occur. The reaction behavior supports a proposed hydroxyl group-limited inhomogeneous bulk reaction mechanism of a colloid type.     

苯并(口恶)嗪改性环氧酸酐体系的固化机理及动力学

利用一种二胺型苯并(口恶)嗪改性环氧酸酐体系。通过FT-IR和DSC分析了改性体系的固化机理。结果表明：共混树脂体系在固化时存在两个反应,首先是环氧树脂与足量的酸酐在咪唑作用下在100℃先开始固化,并在150℃固化2 h后固化完全,之后苯并(口恶)嗪在180℃发生开环聚合。用非等温DSC法研究了该共混体系的固化动力学。采用Flynn-Wall-Ozawa方法求出了共混体系在固化时两个固化反应的活化能,分别为65.27 kJ·mol^-1和92.8 kJ·mol^-1,并利用Friedman方法判断了两个反应都是自催化反应,计算得到自催化模型曲线与实验曲线能较好地吻合。     

Rheological study of the curing kinetics of epoxy–phenol novolac resin

The curing reaction of an epoxy–phenolic resin under different conditions was monitored using rheological measurements. The evolution of viscoelastic properties, such as storage modulus, G′, and loss modulus, G″, was recorded. Several experiments were performed to confidently compare the rheological data obtained under varied curing conditions of temperature, catalyst concentration, and reactive ratios. The values of G′ measured at the end of the reactions (at maximum conversion) were independent of the frequency and temperature of the tests in the range of high temperatures investigated. The overall curing process was described by a second‐order phenomenological rheokinetic equation based on the model of Kamal. The effects of the epoxy‐to‐phenolic ratio as well as the curing temperature and the catalyst concentration were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4430–4439, 2006     

The effect of interpenetrating polymer network formation on polymerization kinetics in an epoxy‐acrylate system

The kinetics of thermally initiated cationic epoxy polymerization and free radical acrylate photopolymerization were studied using photo-differential scanning calorimetry. The reactions of the neat monomers and diluted monomers as well as interpenetrating polymer networks (IPNs) were studied as a function of dilution by the other monomer and temperature. The reaction sequence was also varied to study its effect on the kinetics of formation of the simultaneous IPN's. Both reactions quickly become diffusion controlled. The effects of increasing temperature and dilution on the acrylate polymerization rate profiles are similar, leading to reduced polymerization rate and longer polymerization times. The dilution effect on the epoxy polymerization is similar to that of the acrylate. However, unlike the acrylate reaction the epoxy polymerization rate increases strongly with temperature. The preexistence of one polymer has a significant effect on the polymerization of the second monomer. This effect is larger for the acrylate than for the epoxy polymerization. New kinetic models are needed to capture these complex behaviors.     

Thermal and viscoelastic property of epoxy–clay and hybrid inorganic–organic epoxy nanocomposites

The properties of nanostructured plastics are determined by complex relationships between the type and size of the nanoreinforcement, the interface and chemical interaction between the nanoreinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this article, we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nanoreinforcement, namely, organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nanocomposites were studied using differential scanning calorimetry (DSC). Small-strain stress relaxation under uniaxial deformation was examined to provide insights into the time-dependent viscoelastic behavior of these nanocomposites. Since the size of the POSS macromer is comparable to the distance between molecular junctions, as we increase the amount of POSS macromers, the glass transition temperature T_g as observed by DSC, increases. However, for an epoxy network reinforced with clay, we did not observe any effect on the T_g due to the presence of clay reinforcements. In small-strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely, the characteristic relaxation time, as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS–epoxy nanocomposites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1993–2001, 1999     

The effect of kevlar fiber reinforcement on the curing,thermal, and dynamic‐mechanical properties of an epoxy/anhydride system

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.     

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