Analysis of the cure reaction of carbon nanotubes/epoxy resin composites through thermal analysis and Raman spectroscopy

The effect of the incorporation of single‐walled carbon nanotubes (SWNTs) onto a diglycidyl ether of bisphenol A‐based (DGEBA) epoxy resin cure reaction was investigated by thermal analysis and Raman spectroscopy. The results of the investigation show that SWNTs act as a strong catalyst. A shift of the exothermic reaction peak to lower temperatures is, in fact, observed in the presence of SWNTs. Moreover, these effects are already noticeable at the lowest SWNT content investigated (5%) with slight further effects at higher concentrations, suggesting a saturation of the catalyzing action at the higher concentrations studied. The curves obtained under isothermal conditions confirm the results obtained in nonisothermal tests showing that the cure reaction takes less time with respect to the neat epoxy. The thermal degradation of cured DGEBA and DGEBA/SWNT composites was examined by thermogravimetry, showing a faster thermal degradation for DGEBA–SWNT composites. Raman spectroscopy was successfully applied to demonstrate that the observed changes in the cure reaction of the composites lead to a different residual strain on the SWNT bundles following a different intercalation of the epoxy matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 452–458, 2003     

Novel phosphorus-modified polysulfone as a combined flame retardant and toughness modifier for epoxy resins

A novel phosphorus-modified polysulfone (P-PSu) was employed as a combined toughness modifier and a source of flame retardancy for a DGEBA/DDS thermosetting system. In comparison to the results of a commercially available polysulfone (PSu), commonly used as a toughness modifier, the chemorheological changes during curing measured by means of temperature-modulated DSC revealed an earlier occurrence of mobility restrictions in the P-PSu-modified epoxy. A higher viscosity and secondary epoxy-modifier reactions induced a sooner vitrification of the reacting mixture; effects that effectively prevented any phase separation and morphology development in the resulting material during cure. Thus, only about a 20% increase in fracture toughness was observed in the epoxy modified with 20 wt.% of P-PSu, cured under standard conditions at 180 °C for 2 h. Blends of the phosphorus-modified and the standard polysulfone (PSu) were also prepared in various mixing ratios and were used to modify the same thermosetting system. Again, no evidence for phase separation of the P-PSu was found in the epoxy modified with the P-PSu/PSu blends cured under the selected experimental conditions. The particular microstructures formed upon curing these novel materials are attributed to a separation of PSu from a miscible P-PSu-epoxy mixture. Nevertheless, the blends of P-PSu/PSu were found to be effective toughness/flame retardancy enhancers owing to the simultaneous microstructure development and polymer interpenetration.     

Effect of curing order on the curing kinetics and morphology of bisGMA/DGEBA interpenetrating polymer networks

The curing kinetics and morphology of an interpenetrating polymer network (IPN) formed from an epoxy resin (DGEBA) cured by an imidazole (1‐MeI) and a dimethacrylate resin (bisGMA), cured by low‐ and high‐temperature peroxide initiators (TBPEH and DHPB, respectively) have been studied by temperature‐ramping DSC, isothermal near‐infrared (NIR), DMTA and small‐angle neutron scattering (SANS). bisGMA and DGEBA are polar and chemically similar thermosetting resins which should enhance the miscibility of their IPNs. The phase structure was controlled by varying the curing procedure: the order of gelation of the components is dependent on the choice of low‐ and high‐temperature initiators for bisGMA and this affects the morphology formation. In the cure of the bisGMA/TBPEH:DGEBA/1‐MeI system, the dimethacrylate cures first. For isothermal cure studies at 80 °C, the final conversion of the epoxy is reduced by high crosslinking of the methacrylate groups in the IPN causing vitrification before full cure. The dimethacrylate conversion is enhanced due to plasticisation with unreacted DGEBA, and its cure rate is increased due to accelerated decomposition of TBPEH initiator by 1‐MeI. SANS revealed that phase separation occurs in these IPNs with domains on the scale of 6–7 nm. In the cure of the bisGMA/DHBP:DGEBA/1‐MeI system, the epoxy cures at a similar rate to that of the methacrylate groups. For isothermal cure studies at 80 °C, similar final conversions of the epoxy have been observed except for the 75:25 IPN. The cure rate of the methacrylate groups in the IPN is increased also due to accelerated decomposition of DHBP initiator by 1‐MeI, and the extent of accelerated decomposition for DHBP is stronger than that in the TBPEH‐based systems. SANS studies revealed that this system is more homogeneous due to the rapid formation of the dimethacrylate gel in the presence of the preformed epoxy network which interlocks the networks at low degrees of methacrylate conversion. Copyright © 2006 Society of Chemical Industry     

Crosslinking reaction of epoxy resin (diglycidyl ether of bisphenol A) by anionically polymerized polycaprolactam: I. Mechanism and optimization

Different ratios of epoxy resin, diglycidyl ether of bisphenol A (DGEBA) and ?‐caprolactam (starting from 10:90 DGEBA and vice versa), were used to synthesize reactive DGEBA and polycaprolactam blends by the anionic polymerization of ?‐caprolactam at 140°C. Anionic polymerization was conducted with a strong base such as sodium hydride as a catalyst along with a cocatalyst such as N‐acetyl caprolactam. The reaction mechanism, possible cure reactions, and reaction conditions of the reactive blends were studied with Fourier transform infrared spectroscopy and differential scanning calorimetry. The experiments were carried to study the optimization ratio and the effect of the composition on properties such as hardness and tensile strength of the reactive blends. The DGEBA was crosslinked by polycaprolactam through the reaction of the oxirane group with the amide nitrogen, and the reaction was very fast. A ratio of 80:20 (DGEBA:?‐caprolactam) was optimum, and the resulting blend showed the highest tensile strength and hardness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3237–3247, 2003     

Blends of epoxy resins and polyphenylene oxide as processing aids and toughening agents 2: Curing kinetics,rheology, structure and properties

The curing behaviour, chemorheology, morphology and dynamic mechanical properties of epoxy ? polyphenylene oxide (PPO) blends were investigated over a wide range of compositions. Two bisphenol A based di‐epoxides ? pure and oligomeric DGEBA ? were used and their cure with primary, tertiary and quaternary amines was studied. 4,4′‐methylenebis(3‐chloro‐2,6‐diethylaniline) (MCDEA) showed high levels of cure and gave the highest exotherm peak temperature, and so was chosen for blending studies. Similarly pure DGEBA was selected for blending due to its slower reaction rate because of the absence of accelerating hydroxyl groups. For the PPO:DGEBA340/MCDEA system, the reaction rate was reduced with increasing PPO content due to a dilution effect but the heat of reaction were not significantly affected. The rheological behaviour during cure indicated that phase separation occurred prior to gelation, followed by vitrification. The times for phase separation, gelation and vitrification increased with higher PPO levels due to a reduction in the rate of polymerization. Dynamic mechanical thermal analysis of PPO:DGEBA340/MCDEA clearly showed two glass transitions due to the presence of phase separated regions where the lower T_g corresponded to an epoxy‐rich phase and the higher T_g represented the PPO‐rich phase. SEM observations of the cured PPO:DGEBA340/MCDEA blends revealed PPO particles in an epoxy matrix for blends with 10 wt% PPO, co‐continuous morphology for the blend with 30 wt% PPO and epoxy‐rich particles dispersed in a PPO‐rich matrix for 40wt% and more PPO. © 2014 Society of Chemical Industry     

Reaction and miscibility of two diepoxides with poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) was melt‐blended at 270°C with two epoxy monomers, diglycidyl ether of bisphenol A (DGEBA) and 3,4‐epoxycyclohexyl‐methyl‐3,4‐epoxycyclohexyl carboxylate (ECY). Intermediate proportions of the epoxy in the range of 20–0.5 wt % were used. If the epoxy monomers were added in a high proportion (10–20%), a large fraction did not react with PET. Calorimetric experiments showed that the unreacted fractions of both epoxies were miscible with the amorphous phase of the polyester. Only one glass‐transition temperature was detected. It was depressed as the epoxy content was increased. The transition was broad when the PET component was crystalline, and it was narrow when the PET component was made amorphous by quenching of the blend. These features were confirmed by dynamic thermal mechanical analysis. As is often the case for crystalline blends, the crystallization and melting temperatures decreased when the proportion of the epoxy was increased. Concerning the reactivity of the epoxy with PET, the behavior differed according to the nature of the epoxy. The DGEBA monomer showed a low reactivity. It was not effective for the chain extension of PET, and no increase in the intrinsic viscosity was observed under the experimental conditions. However, some functionalization of the chain ends may be possible at a high concentration of the epoxy. ECY was more reactive, and the molecular weight of the processed PET increased, although the value of the commercial untreated polyester was not attained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1995–2003, 2003     

Toughening of epoxy resin systems using low‐viscosity additives

This study has evaluated three low‐viscosity epoxy additives as potential tougheners for two epoxy resin systems. The systems used were a lower‐reactive resin based upon the diglycidyl ether of bisphenol A (DGEBA) and the amine hardener diethyltoluene diamine, while the second epoxy resin was based upon tetraglycidyl methylene dianiline (TGDDM) and a cycloaliphatic diamine hardener. The additives evaluated as potential tougheners were an epoxy‐terminated aliphatic polyester hyperbranched polymer, a carboxy‐terminated butadiene rubber and an aminopropyl‐terminated siloxane. This work has shown that epoxy‐terminated hyperbranched polyesters can be used effectively to toughen the lower cross‐linked epoxy resins, i.e. the DGEBA‐based systems, with the main advantage being that they have minimal effect upon processing parameters such as viscosity and the gel time, while improving the fracture properties by about 54 % at a level of 15 wt% of additive and little effect upon the T_g. This result was attributed to the phase‐separation process producing a multi‐phase particulate morphology able to initiate particle cavitation with little residual epoxy resin dissolved in the continuous epoxy matrix remaining after cure. The rubber additive was found to impart similar levels of toughness improvement but was achieved with a 10–20 °C decrease in the T_g and a 30 % increase in initial viscosity. The siloxane additive was found not to improve toughness at all for the DGEBA‐based resin system due to the poor dispersion within the epoxy matrix. The TGDDM‐based resin systems were found not to be toughened by any of the additives due to the lack of plastic deformation of the highly cross‐linked epoxy network Copyright © 2003 Society of Chemical Industry     

Curing kinetics and reaction‐induced homogeneity in networks of poly(4‐vinyl phenol) and diglycidylether epoxide cured with amine

Mixtures of diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin with poly(4‐vinyl phenol) (PVPh) of various compositions were examined with a differential scanning calorimeter (DSC), using the curing agent 4,4′‐diaminodiphenylsulfone (DDS). The phase morphology of the cured epoxy blends and their curing mechanisms depended on the reactive additive, PVPh. Cured epoxy/PVPh blends exhibited network homogeneity based on a single glass transition temperature (T_g) over the whole composition range. Additionally, the morphology of these cured PVPh/epoxy blends exhibited a homogeneous network when observed by optical microscopy. Furthermore, the DDS‐cure of the epoxy blends with PVPh exhibited an autocatalytic mechanism. This was similar to the neat epoxy system, but the reaction rate of the epoxy/polymer blends exceeded that of neat epoxy. These results are mainly attributable to the chemical reactions between the epoxy and PVPh, and the regular reactions between DDS and epoxy. Polym. Eng. Sci. 45:1–10, 2005. © 2004 Society of Plastics Engineers.     

Poly(phenylene ether)/epoxy thermoset blends based on anionic polymerization of epoxy monomer

Low molar mass poly (phenylene ether) (LMW‐PPE) with phenol‐reactive chain ends was used as modifier of epoxy thermoset. The epoxy monomer was diglycidylether of bisphenol A (DGEBA), and several imidazoles were used as initiators of anionic polymerization. The curing and phase separation processes were investigated by different techniques: Differential Scanning Calorimetry, Size Exclusion Chromatography, and Light Transmission measurements. The final morphology of blends was observed by Environmental Scanning Electron Microscopy and Transmission Electron Microscopy. The epoxy network is obtained by imidazole initiated DGEBA homopolymerization. Initial LMW‐PPE/DGEBA mixtures show an UCST behavior with cloud point temperatures between 40 and 90°C. PPE phenol end‐groups can react with epoxy, leading to a better interaction between phases. The curing mechanism and phase separation process are not influenced by the chemical structure of initiators, except when reactive amine groups are present. The phase inversion is observed at 30 wt % of PPE. The mixtures with amine‐substituted imidazole present important differences in the initial miscibility and curing process interpreted in terms of fast room temperature amine‐epoxy reaction during blending. Final domain size is affected by this prereaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2678–2687, 2004     

Clay‐reinforced epoxy nanocomposites

Epoxy/clay nanocomposites were prepared using a conventional diglycidyl ether of bisphenol A (DGEBA) epoxy, cured with diethyltoluene diamine (DETDA). The nanocomposites were characterized by dynamic mechanical analysis. A modest increase in glass transition temperature and significant increase in storage modulus were achieved as a result of incorporation of clay. The formation of nanocomposite was confirmed by wide‐angle X‐ray analysis. The higher impact strength of the nanocomposite compared the DGEBA matrix was explained in terms of with the morphology observed by SEM. © 2003 Society of Chemical Industry     

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     

Rubber modified epoxy resin. II: Phase separation behavior

DGEBA (diglycidyl ether of bisphenol A)–ATBN (amine terminated butadiene acrylonitrile copolymer) blends exhibited upper critical solution temperature (UCST) behavior. Triethylene tetramine (TETA) was introduced as an amine curing agent of epoxy. The real-time phase separation behavior of ATBN-added epoxy system during cure was investigated using laser light scattering. SEM (scanning electron microscopy) and optical microscopy were also employed to observe the morphology of the epoxy blends. Since the DGEBA–ATBN blends showed UCST behavior, the degree of phase separation when cured at low temperature was higher than that when cured at high temperature. The domain correlation length increased as the curing temperature was lowered. Dynamic mechanical analysis (DMA) results indicated that the phase inversion occurred above 20 wt% of ATBN composition.     

Studies on the curing and thermal behaviour of DGEBA in the presence of bis(4‐carboxyphenyl) dimethyl silane

The curing behaviour of diglycidyl ether of bisphenol‐A (DGEBA) was investigated by differential scanning calorimetry using bis(4‐carboxyphenyl) dimethyl silane (CPA) as a crosslinking agent and imidazole as a catalyst. Two exotherms were observed in the absence of catalyst in the temperature range 166–328 °C. A significant decrease in the curing temperature was observed when 0.1% imidazole was used as catalyst. Further increase in the concentration of imidazole resulted in a decrease in the peak exotherm temperature. The effect of stoichiometry of functional groups on the curing behaviour of DGEBA was investigated by taking varying mole ratios of CPA, ranging from 1 to 2.5, keeping the concentration of imidazole as 0.1% w/w. The heat of polymerization (ΔH) was found to be maximum at a molar ratio of 1:1.75 (DGEBA:CPA). Mixtures of diaminodiphenyl sulfone (DDS and CPA or phthalic anhydride (PA) and CPA in ratios of 1:0, 0.25:0.75, 0.5:0.5, 0.75:0.25) were also used to investigate the curing behaviour of DGEBA. A significant decrease in curing temperature of DGEBA/DDS was observed on partially replacing DDS with CPA, whereas marginal change in the curing temperatures was observed on replacing phthalic anhydride with CPA. The thermal stability of epoxy resin, cured isothermally, was evaluated by recording thermogravimetry/dynamic thermogravimetry traces in nitrogen atmosphere. The percentage char yield was highest for the sample cured using 1.75 mole of CPA. Copyright © 2003 Society of Chemical Industry     

Study of crosslinking acid copolymer/DGEBA systems by FTIR

A study of crosslinking of diglycidylether of bisphenol A (DGEBA) by four copolymers of poly(acrylic acid‐co‐styrene) having different acid group percentages, in the range 7.6–76.6%, was done by FTIR. The study was done in the isothermal mode for four different temperatures, the reaction being accelerated by triethylamine. We followed each by temperature and the variation of the area of the epoxy infrared band (912–916 cm^?1) versus time. The results showed that the mechanism was complex and depended on the acid composition in the copolymer. Three types of reaction were involved: addition esterification, etherification, and condensation esterification. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2033–2051, 2003     

Properties of impregnation resin added to multifunctional epoxy at cryogenic temperature

A multifunctional epoxy tetraglycidyl dibenzmethyldiamine and triglycidyl benzylamine were blended, respectively, into impregnation resin, which mainly consists of diglycidyl ether of bisphenol A (DGEBA) and acid anhydride hardener. This resin is expected to impregnate HT‐7U superconducting Tokamak toroidal field coils and improve the fracture toughness of DGEBA–acid anhydride resin at cryogenic temperature. However, the experimental results reveal that resin lap shear strengths decrease remarkably both at ambient and liquid nitrogen temperatures. After blending multifunctional epoxy for several hours, its viscosity increased quickly at room temperature. The usable potting life is too short to impregnate large coils such as those used in fusion reaction. By FTIR the possible reason was investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1385–1389, 2003     

Effect of microencapsulated curing agents on the curing behavior for diglycidyl ether of bisphenol A epoxy resin systems

Microcapsules containing a curing agent, 2‐phenyl imidazole (2PZ), for a diglycidyl ether of bisphenol A (DGEBA) epoxy resin were prepared by a solid‐in‐oil‐in‐water emulsion solvent evaporation technique with poly(methyl methacrylate) (PMMA) as a polymeric wall. The mean particle size of the microcapsules and the concentration of 2PZ were about 10 μm and nearly 10 wt %, respectively. The onset cure temperature and peak temperature of the DGEBA/2PZ–PMMA microcapsule system appeared to increase by nearly 30 and 10°C, respectively, versus those of the DGEBA/2PZ system because of the increased reaction energy of curing. The former could take more than 3 months at room temperature, whereas the latter was cured after only a week. The values of the reaction order (a curing kinetic parameter) for DGEBA/2PZ and DGEBA/2PZ–PMMA microcapsules were quite close, and this showed that the curing reactions of the two samples proceeded conformably. The curing mechanism was investigated, and a two‐step initiation mechanism was considered: the first was assigned to adduct formation, whereas the second was due to alkoxide‐initiated polymerization. The glass‐transition temperature of DGEBA/2PZ was 165.2°C, nearly 20°C higher than the glass‐transition temperatures of DGEBA/2PZ–PMMA microcapsules and DGEBA/2PZ/PMMA microspheres, as determined by differential scanning calorimetry measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

The preparation and morphology of PPO–epoxy blends

Poly(phenylene oxide) (PPO) was found to be miscible in diglycidyl ether of bisphenol A (DGEBA) based epoxy. The PPO–DGEBA system exhibited upper critical solution temperature (UCST) behavior. The cloud point temperatures were measured and found to be sensitive to the mol wt of the epoxy resin. A series of PPO-modified epoxies were cured with piperidine at 160°C, which is above the cloud point temperature. Upon cure, two phase solids were formed, which contained discrete PPO particles. However, the two-phase particulate morphology was not uniform and numerous large, occluded PPO particles were observed. In order to improve the uniformity, several styrene-maleic anhydride copolymers were evaluated as potential surfactants for PPO-DGEBA bends. The formation of a uniform, particulate morphology was facilitated by the addition of a styrene–maleic anhydride copolymer, containing a 10:1 ratio of styrene to maleic anhydride. To our knowledge, this is the first time that an emulsifying agent has been added to improve the morphology of thermoplastic modified epoxies. © 1993 John Wiley & Sons, Inc.     

Azo initiator selection to control the curing order in dimethacrylate/epoxy interpenetrating polymer networks

Differential Scanning calorimetry (DSC) and Fourier‐transform infrared (FT‐IR) spectroscopic studies have been undertaken of the cure of interpenetrating polymer networks (IPNs) formed with imidazole‐cured diglycidyl ether bisphenol‐A (DGEBA) and with either diethoxylated bisphenol‐A dimethacrylate (DEBPADM) or bisphenol‐A diglycidyl dimethacrylate (bisGMA), polymerized by a range of azo initiators (AIBN64, VAZ088, VR110 and AZO168). Due to the differing decomposition rates of the azo initiators, the neat dimethacrylate resin either cured faster than (with AIBN64 and VAZO88), or similar to (VR110), or slower than (AZO168), the neat epoxy resin. In the neat DGEBA/1‐methyl imidazole (1‐MeI), DEBPADM/AIBN64, DEBPADM/VAZO88 and DEBPADM/VR110 resins, close to full cure was achieved. For the neat, high‐temperature DEBPADM/AZO168 resin, full cure was not attained, possibly due to the compromise between using a high enough temperature for azo decomposition while avoiding depolymerization or decomposition of the methacrylate polymer. IPN cure studies showed that, by appropriate initiator selection, it was possible to interchange the order of cure of the components within the IPN so that either the dimethacrylate or epoxy cured first. In the isothermal cure of the 50:50 DEBPADM/AIBN64:DGEBA/1‐Mel IPN system, the cure rate of both species was less than in the parent resins, due to a dilution effect. For this system, the dimethacrylate cured first and to high conversion, due to plasticization by the unreacted epoxy, but the subsequent cure of the more slowly polymerizing epoxy component was restricted by the high crosslink density developed in the IPN. After post‐curing, however, high conversion of both reactive groups was observed and the fully cured IPN exhibited a single high‐temperature T_g, close to the T_g values of the parent resins. In the higher‐temperature, isothermal cure of the 50:50 DEBPADM/VR110:DGEBA/1‐Mel IPN system, the reactive groups cured at a similar rate and so the final conversions of both groups were restricted, while in the 50:50 DEBPADM/AZO168:DGEBA/1‐Mel system it was the epoxy which cured first. Both of these higher‐temperature azo‐initiated IPN systems exhibited single T_gs, indicating a single‐phase structure; however, the T_gs are significantly lower than expected, due to plasticization by residual methacrylate monomer and/or degradation products resulting from the high cure temperature. Copyright © 2004 Society of Chemical Industry     

Morphology profiles obtained by reaction‐induced phase separation in epoxy/polysulfone/poly(ether imide) systems

The reaction‐induced phase separation in epoxy/aromatic diamine formulations simultaneously modified with two immiscible thermoplastics (TPs), poly(ether imide) (PEI) and polysulfone (PSF), has been studied. The epoxy monomer was based on the diglycidyl ether of bisphenol A (DGEBA) and the aromatic diamine was 4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) (MCDEA). Phase‐separation conversions are reported for various PSF/PEI proportions for blends containing 10 wt% total TP. On the basis of phase‐separation results, a conversion–composition phase diagram at 200 °C was compiled. This diagram was used to design particular cure cycles in order to generate different morphologies during the phase‐separation process. It was found that, depending on the PSF/PEI ratio employed, a particulate or a morphology characterized by a distribution of irregular PEI‐rich domains dispersed in an epoxy‐rich phase was obtained for initially miscible blends. Scanning electron microscopy (SEM) characterization revealed that the PEI‐rich phase exhibits a phase‐inverted structure and the epoxy‐rich matrix presents a bimodal size distribution of TP‐rich particles. For PSF/PEI ratios near the miscibility limit, slight temperature change result in morphology profiles. Copyright © 2005 Society of Chemical Industry