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     

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     

Modeling the curing kinetics for a modified bismaleimide resin

The kinetics of curing for a modified bismaleimide (BMI) has been investigated to ascertain a suitable cure model for the material. The experimental data for characterizing the curing kinetics for a modified bismaleimide resin were determined using a DSC isothermal scan method and indicated a curing mechanism involving multiple reactions. The reaction process was shown to be dominated by a different mechanism at different stages of the cure process, with an initial autocatalytic reaction shifting into an nth order reaction as the reaction proceeded. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 907–913, 2000     

Cure Kinetics of Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine System

The cure kinetics of epoxy based on the diglycidyl ether of bisphenol A (DGEBA) modified with different amounts of poly(acrylonitrile-butadiene-styrene) (ABS) and cured with 4,4′-diaminodiphenylsulfone (DDS) was investigated by employing differential scanning calorimetry (DSC). The curing reaction was followed by using an isothermal approach over the temperature range 150–180°C. The amount of ABS in the blends was 3.6, 6.9, 10 and 12.9 wt%. Blending of ABS in the epoxy monomer did not change the reaction mechanism of the epoxy network formation, but the reaction rate seems to be decreased with the addition of the thermoplastic. A phenomenological kinetic model was used for kinetic analysis. Activation energies and kinetic parameters were determined by fitting the kinetic model with experimental data. Diffusion control was incorporated to describe the cure in the latter stages, predicting the cure kinetics over the whole range of conversion. The reaction rates for the epoxy blends were found to be lower than that of the neat epoxy. The reaction rates decreased when the ABS contents was increased, due to the dilution effect caused by the ABS on the epoxy/amine reaction mixture.     

Phase separation,porous structure,and cure kinetics in aliphatic epoxy resin containing hyperbranched polyester

Thermosetting blends of an aliphatic epoxy resin and a hydroxyl‐functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 4,4′‐diaminodiphenylmethane (DDM) as the curing agent. The phase behavior and morphology of the DDM‐cured epoxy/HBP blends with HBP content up to 40 wt % were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The cured epoxy/HBP blends are immiscible and exhibit two separate glass transitions, as revealed by DMA. The SEM observation showed that there exist two phases in the cured blends, which is an epoxy‐rich phase and an HBP‐rich phase, which is responsible for the two separate glass transitions. The phase morphology was observed to be dependent on the blend composition. For the blends with HBP content up to 10 wt %, discrete HBP domains are dispersed in the continuous cured epoxy matrix, whereas the cured blend with 40 wt % HBP exhibits a combined morphology of connected globules and bicontinuous phase structure. Porous epoxy thermosets with continuous open structures on the order of 100–300 nm were formed after the HBP‐rich phase was extracted with solvent from the cured blend with 40 wt % HBP. The DSC study showed that the curing rate is not obviously affected in the epoxy/HBP blends with HBP content up to 40 wt %. The activation energy values obtained are not remarkably changed in the blends; the addition of HBP to epoxy resin thus does not change the mechanism of cure reaction of epoxy resin with DDM. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 889–899, 2006     

Evaluation of solubility parameters during polymerisation of amine‐cured epoxy resins

A new procedure for the calculation of solubility parameter evolution during polymerisation has been developed for amine‐cured epoxy systems, which allows quantitative thermodynamic modelling of chemically induced phase separation (CIPS). Solubility parameters calculation, chemical analysis based on near infrared spectroscopy and curing kinetics results obtained by differential scanning calorimetry will allow to model the evolution of the Flory–Huggins interaction parameter in amine‐cured epoxy blends. The resin system investigated was based on a diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with isophorone diamine (IPD) blended with various reactive epoxydised dendritic hyperbranched polymer modifiers (HBP), yielding a CIPS‐controlled morphology. The analysis showed the evolution of the different contributions to the solubility parameters to follow the polymerisation kinetics. The dispersive contribution had the highest value at all stages of polymerisation, but the hydrogen and polar contributions showed the largest variation. By evaluating the dynamic evolution of the solubility parameter components, the Flory–Huggins interaction parameter in the epoxy resin‐hyperbranched polymer blends has been modelled as a function of time. This procedure, combined with thermodynamic modelling, will enable to predict phase diagrams in CIPS thermosetting blends quantitatively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1883–1892, 2000     

酸酐固化环氧树脂/蒙脱土复合材料的等温固化动力学

用等温差示扫描量热法(DSC)研究了酸酐固化环氧树脂/蒙脱土复合材料的等温固化过程，考察了未处理的蒙脱土(MMT)和有机蒙脱土(OMMT)对环氧树脂固化动力学的影响. 实验表明， 环氧树脂的固化过程包含自催化机理，加入蒙脱土没有改变固化反应机理. 用Kamal方程对该体系的固化过程进行拟合，得到反应级数m、n，反应速率常数k1、k2，总反应级数(m + n)在2.4～3.0之间. MMT的加入使环氧树脂体系的k1、k2有所降低，而OMMT的加入对体系的k1、k2影响较为复杂，加入蒙脱土对环氧树脂固化体系的活化能影响较小.     

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     

Cationic cure kinetics of a polyoxometalate loaded epoxy nanocomposite

The reaction cure kinetics of a novel polyoxometalate (POM) loaded epoxy nanocomposite is described. The POM is dispersed in the epoxy resin up to volume fractions of 0.1. Differential scanning calorimetry measurements show the cure of the epoxy resin to be sensitive to the POM loading. A kinetics study of the cure exotherm confirms that POM acts as a catalyst promoting cationic homopolymerization of the epoxy resin. The cure reaction is shown to propagate through two cure regimes. A fast cure at short time is shown to be propagation by the activated chain end (ACE) mechanism. A slow cure at long time is shown to be propagation by the activated monomer (AM) mechanism. The activation energies for the fast and slow cure regimes agree well with other epoxy based systems that have been confirmed to propagate by the ACE and AM mechanisms.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of the substituted benzene group on thermal and mechanical properties of epoxy resins initiated by cationic latent catalysts

Epoxy resins (DGEBA) were cured by cationic latent thermal catalysts, that is, N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH) to investigate the effect of substituted benzene group on cure kinetics and mechanical properties of epoxy system. Differential scanning calorimetry (DSC) was undertaken for activation energy of the system. It was also characterized in terms of flexural, fracture toughness, and Izod impact strengths for the mechanical tests. As a result, the cure reaction of both epoxy systems resulted in an autocatalytic kinetic mechanism accelerated by hydroxyl groups. Also, the conversion and cure activation energy of the DGEBA/BQH system were higher than those of DGEBA/BPH system. The mechanical properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system, as well as the morphology. This was probably due to the consequence of the effect of the substituted benzene group of the BQH catalyst, resulting in increasing the crosslinking density and structural stability in the epoxy system studied. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2419–2429, 2004     

Kinetics and mechanistic investigation of epoxy–anhydride compositions cured with quaternary phosphonium salts as accelerators

Mechanism and curing kinetics of bisphenol A epoxy resin–iso‐methyltetrahydrophthalic anhydride compositions using quaternary phosphonium salts as accelerators were investigated by differential scanning calorimetry (DSC) and electrospray mass‐spectrometry (ESI‐MS). The DSC method was applied to investigate curing kinetics and apparent activation energy values for the overall curing process. The DSC results showed that some of the phosphonium salts lead to a lower activation energy, that means they are more effective accelerators for the curing of epoxy–anhydride systems. The mechanism of curing was studied by ESI‐MS using the model reaction of epichlorohydrin (E) with phthalic anhydride (PA) in the presence of phosphonium salts or 2‐methylimidazole. Products containing the alkyl moiety of the phosphonium salt in form of alkyl esters could be identified. This suggests that the phosphonium salts activate the anhydride by electrophilic attack. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1088–1097     

High melting thermoplastic/epoxy resin blends: Influence of the curing reaction on the crystallization and melting behavior

The influence of the cure process and the resulting reaction‐induced phase separation (RIPS) on the crystallization and melting behavior of polyoxymethylene (POM) in epoxy resin diglycidylether of bisphenol A (DGEBA) blends has been studied at different cure temperatures (180 and 145 °C). The crystallization and melting behavior of POM was studied with DSC and the simultaneous blend morphology changes were studied using OM. At first, the influence of the epoxy monomer on the dynamically crystallized POM was investigated. Secondly, a cure temperature above the melting point of POM (T_cure = 180 °C) was applied for blends with curing agent to study the influence of resulting phase morphology types on the crystallization behavior of POM in the epoxy blends. Large differences between particle/matrix and phase‐inverted structures have been observed. Thirdly, the cure temperature was lowered below the melting temperature of POM, inducing isothermal crystallization prior to RIPS. As a consequence, a distinction was made between dynamically and isothermally crystallized POM. Concerning the dynamically crystallized material, a clear difference could be made between the material crystallized in the homogeneous sample and that crystallized in the phase‐separated structures. The isothermally crystallized POM was to a large extent influenced by the conversion degree of the epoxy resin. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2456–2469, 2007     

Cure kinetics of epoxy resin-natural zeolite composites

The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate.     

Curing kinetics of epoxy resins with hyperbranched polyesters as toughening agents

The effects of hyperbranched polyesters on the cure kinetics of diglycidyl ether of bisphenol A (DGEBA) in the presence of m‐phenylene diamine were investigated with nonisothermal differential scanning calorimetry. The results showed that the addition of hyperbranched polyesters enhanced the cure reaction of DGEBA with m‐phenylene diamine, and this resulted in a reduction of the peak temperature of the curing curve and the activation energy because of the low viscosity and large number of terminal hydroxyl groups. However, when linear poly(ethylene glycol) was added, the activation energy of the blends also slightly decreased, whereas the peak temperature of the curing curve increased. The curing kinetics of the blends were calculated by the isoconversional method of Málek. The two‐parameter autocatalytic model (i.e., the ?esták–Berggren equation) was found to be the most adequate for describing the cure kinetics of the studied systems. The obtained nonisothermal differential scanning calorimetry curves showed results in agreement with those theoretically calculated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2649–2656, 2004     

Kinetics studies on the accelerated curing of liquid crystalline epoxy resin/multiwalled carbon nanotube nanocomposites

A new class of nanocomposite has been fabricated from liquid crystalline (LC) epoxy resin of 4,4′‐bis(2,3‐epoxypropoxy) biphenyl (BP), 4,4′‐diamino‐diphenyl sulfone (DDS), and multiwalled carbon nanotubes (CNTs). The surface of the CNTs was functionalized by LC epoxy resin (ef‐CNT). The ef‐CNT can be blended well with the BP that is further cured with an equivalent of DDS to form nanocomposite. We have studied the curing kinetics of this nanocomposite using isothermal and nonisothermal differential scanning calorimetry (DSC). The dependence of the conversion on time can fit into the autocatalytic model before the vitrification, and then it becomes diffusion control process. The reaction rate increases and the activation energy decreases with increasing concentration of the ef‐CNT. At 10 wt % of ef‐CNT, the activation energy of nanocomposite curing is lowered by about 20% when compared with the neat BP/DDS resin. If the ef‐CNT was replaced by thermal‐insulating TiO₂ nanorods on the same weight basis, the decrease of activation energy was not observed. The result indicates the accelerating effect on the nanocomposite was raised from the high‐thermal conductivity of CNT and aligned LC epoxy resin. However, at ef‐CNT concentration higher than 2 wt %, the accelerating effect of ef‐CNTs also antedates the vitrification and turns the reaction to diffusion control driven. As the molecular motions are limited, the degree of cure is lowered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Toughening of nylon‐6 with epoxy‐functionalized acrylonitrile‐butadiene‐styrene copolymer

Glycidyl methacrylate (GMA) functionalized acrylonitrile‐butadiene‐styrene (ABS) copolymers have been prepared via an emulsion polymerization process. The epoxy‐functionalized ABS (e‐ABS) particles were used to toughen nylon‐6. Molau tests and FTIR results showed the reactions between nylon‐6 and e‐ABS have taken place. Scanning electron microscopy (SEM) displayed the compatibilization reaction between epoxy groups of e‐ABS and nylon‐6 chain ends (amine or carboxyl groups), which improve disperse morphology of e‐ABS in the nylon‐6 matrix. The presence of only a small amount of GMA (1 wt %) within the e‐ABS copolymer was sufficient to induce a pronounced improvement of the impact strength of nylon‐6 blends; whereas further increase of the GMA contents in e‐ABS resulted in lower impact strength because of the crosslinking reaction between nylon‐6 and e‐ABS, resulting in agglomeration of the ABS particles. SEM results showed shear yielding of the nylon‐6 matrix and cavitation of rubber particles were the major toughening mechanisms. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2170–2180, 2005     

Reactive compatibilization of polyamide‐6 (PA 6)/polybutylene terephthalate (PBT) blends by a multifunctional epoxy resin

A multifunctional epoxy resin has been demonstrated to be an efficient reactive compatibilizer for the incompatible and immiscible blends of polyamide‐6 (PA 6) and polybutylene terephthalate (PBT). The torque measurements give indirect evidence that the reaction between PA and PBT with epoxy has an opportunity to produce an in situ formed copolymer, which can be as an effective compatibilizer to reduce and suppress the size of the disperse phase, and to greatly enhance mechanical properties of PA/PBT blends. The mechanical property improvement is more pronounced in the PA‐rich blends than that in the PBT‐rich blends. The fracture behavior of the blend with less than 0.3 phr compatibilizer is governed by a particle pullout mechanism, whereas shear yielding is dominant in the fracture behavior of the blend with more than 0.3 phr compatibilizer. As the melt and crystallization temperatures of the base polymers are so close, either PA or PBT can be regarded as a mutual nucleating agent to enhance the crystallization on the other component. The presence of compatibilizer and in situ formed copolymer in the compatibilized blends tends to interfere with the crystallization of the base polymers in various blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 23–33, 2000     

The kinetics of the epoxy amine cure reaction from a solvation perspective

This article investigates the role of solvation effects in the autocatalysis reaction of the epoxy–amine cure reaction. A single‐phase three component model was developed encompassing a two‐component reaction mix and a single polymeric product. The reaction was modelled as an S_N2 reaction. Association of the nucleophile with each component in the reaction was defined via a binding constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3579–3586, 2004     

Phase behavior and photocrosslinking kinetics of semi-interpenetrating polymer networks prepared from miscible polymer blends

Mixtures of polystyrene derivatives (PSCS) and poly(vinyl methyl ether) (PVME) were made photocrosslinkable by chemically labeling PSCS chains with photoreactive anthracene. Miscibility of these anthracene-labeled PSCS/PVME blends was examined by light scattering under several crosslinking conditions in the one-phase region via photodimerization of anthracenes. As the reaction proceeds, the coexistence curve of PSCS/PVME blends shifts toward the low temperature side. By following the changes in concentration of anthracenes with irradiation time, it was found that the crosslinking reaction of PSCS chains in the blends does not follow the mean-field kinetics. However, it can be well expressed by the Kohlrausch–Williams–Watts (KWW) relaxation mechanism, indicating that the crosslinking reaction proceeds inhomogeneously in the blends. By scaling the reaction time with the average reaction rate obtained from the KWW equation modified for the reaction kinetics, all the crosslinking data obtained in the miscible region of the reacted blends fall on a single master curve. These experimental results suggest the universal behavior of the photocrosslinking kinetics obtained under the “shallow quench” conditions in the region far away from the coexistence curve of the reacting blends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 455–462, 1998     

Near‐infrared spectroscopic studies on the cure behaviors of the CAE/DGEBA blend system initiated by a thermal latent catalyst

The latent properties and cure behaviors of an epoxy blend system based on cycloaliphatic epoxy (CAE) and diglycidyl ether of bisphenol A (DGEBA) epoxy containing N‐benzylpyrazinium hexafluoroantimonate (BPH) as a thermal latent initiator were investigated with near‐infrared (N‐IR) spectroscopy. The assignments of the latent properties and cure kinetics were performed by the measurements of the N‐IR reflectance for epoxide and hydroxyl functional groups at different temperatures and compositions. As a result, this system showed more than one type of reaction, and BPH was an excellent thermal latent catalyst without any coinitiator. The cure behaviors were identified by the changes in the absorption intensity of the hydroxyl groups at 7100 cm⁻¹ with different composition ratios. Moreover, characteristic N‐IR band assignments were used to evaluate the reactive kinetics and were shown to be an appropriate method for studying the cure behaviors of the CAE/DGEBA blend system containing a thermal latent catalyst. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 326–331, 2001