Effects of rubber‐rich domains and the rubber‐plasticized matrix on the fracture behavior of liquid rubber‐modified araldite‐F epoxies

The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl‐terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, K_IC, measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber‐rich domains and the structure of the rubber‐rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy‐residing dispersed rubber phase and the rubber‐dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process.     

Nanoinduced morphology and enhanced properties of epoxy containing tungsten disulfide nanoparticles

Closed‐cage (fullerene‐like) nanoparticles (NPs) of WS₂ are currently produced in large amounts and were investigated as additives to thermoplastics and thermosetting polymers. The nanoinduced morphology and the resulting enhanced fracture toughness of epoxy/WS₂ nanocomposites were studied. The morphology of the epoxy nanocomposites was induced by controlled WS₂ surface chemistry. The WS₂ NPs used were either untreated or chemically treated with acryloxy, which is compatible, and alkyl silane, which is incompatible, respectively, with the epoxy matrix. In the case where the acryloxy silane was used to treat the WS₂ particles, good dispersion and compatibility were obtained in the epoxy resin_. Moreover, a distinct nodular morphology was induced on fracture as a result of nucleation by the compatible NPs. In the case where the alkyl silane treatment was used cavitation morphology was induced, following mechanical loading, which is the result of incompatibility with the epoxy resin. The fracture toughness results showed an increase of 70% for nanocomposites contains alkyl‐treated WS₂ compared with the neat epoxy. Modeling of the nodular morphology enabled the determination of optimal concentration of the WS₂ in epoxy (0.3% by weight). Two main fracture mechanisms were observed, crack bowing around the nodular boundaries in the case of compatibility between the nanoparticle and the epoxy and particle‐induced cavitation in the case of incompatibility, respectively. These results are of significant importance both for epoxy‐based adhesives and fiber composites. POLYM. ENG. SCI., 53:2624–2632, 2013. © 2013 Society of Plastics Engineers     

Enhanced fracture toughness of epoxy resins with novel amine‐terminated poly(arylene ether sulfone)–carboxylic‐terminated butadiene‐acrylonitrile–poly(arylene ether sulfone) triblock copolymers

Amine‐terminated poly(arylene ether sulfone)–carboxylic‐terminated butadiene‐acrylonitrile–poly(arylene ether sulfone) (PES‐CTBN‐PES) triblock copolymers with controlled molecular weights of 15,000 (15K) or 20,000 (20K) g/mol were synthesized from amine‐terminated PES oligomer and commercial CTBN rubber (CTBN 1300x13). The copolymers were utilized to modify a diglycidyl ether of bisphenol A epoxy resin by varying the loading from 5 to 40 wt %. The epoxy resins were cured with 4,4′‐diaminodiphenylsulfone and subjected to tests for thermal properties, plane strain fracture toughness (K_IC), flexural properties, and solvent resistance measurements. The fracture surfaces were analyzed with SEM to elucidate the toughening mechanism. The properties of copolymer‐toughened epoxy resins were compared to those of samples modified by PES/CTBN blends, PES oligomer, or CTBN. The PES‐CTBN‐PES copolymer (20K) showed a K_IC of 2.33 MPa m^0.5 at 40 wt % loading while maintaining good flexural properties and chemical resistance. However, the epoxy resin modified with a CTBN/8K PES blend (2:1) exhibited lower K_IC (1.82 MPa m^0.5), lower flexural properties, and poorer thermal properties and solvent resistance compared to the 20K PES‐CTBN‐PES copolymer‐toughened samples. The high fracture toughness with the PES‐CTBN‐PES copolymer is believed to be due to the ductile fracture of the continuous PES‐rich phases, as well as the cavitation of the rubber‐rich phases. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1556–1565, 2002; DOI 10.1002/app.10390     

Microstructure,mechanical properties,and fracture behavior of liquid rubber toughened thermosets

Phenolic epoxy resin was toughened by carboxyl-randomized butadiene acrylonitrile copolymer (CRBN) for use as composite matrix. By adding different parts of butadiene acrylonitrile copolymer (BN-26, without carboxyl contained) to CRBN, different sizes of rubber domains and different numbers of chemical bondings between the resin matrix and the rubber phase were obtained. It is found that small rubber particles (less than 0.1 μm) are cavitated during the crack development. The interaction between secondary crack zones caused by the cavitation makes the fracture toughness K_IC of the materials high; by comparison, a local stress-whitened zone is produced in the material with large rubber particles (more than 0.1 μm) when it is subjected to tensile stress. In this case, the flexure strength σ_f of the material is great. Using ultrasection and TEM techniques, the stress-whitened zone was shown to be caused by the special multiple-phase structure of the material, in which many caves and “macrocrazes” coexist.     

Modification of epoxy resins with acrylic rubbers containing a pendant epoxy group

New acrylic rubbers with a pendant epoxy group were prepared by copolymerization of butyl acrylate (BA) with vinylbenzyl glycidyl ether (VBGE). The modification of an epoxy system (bisphenol-A diglycidyl ether/p,p′-diaminodiphenyl sulfone) with the acrylic rubbers was carried out in order to increase the toughness of the cured epoxy resin. The addition of 20 wt.-% of the copolymer containing 74% of BA and 26% of VBGE units resulted in a 30% increase in the fracture toughness (K_IC) of the cured resin at minimal expenses of strength and modulus of the resin. The modified epoxy resin had two-phase morphology in which the rubber particles with average diameter of 2 μm are dispersed in the epoxy matrix. The copolymer without the pendant epoxy group, prepared from BA and vinylbenzyl methoxyethyl ether, was ineffective as a modifier, indicating that the reaction of the pendant epoxide with the epoxy matrix resulted in good interfacial adhesion between the rubber particles and the matrix, and in the increased toughness. The epoxide-containing copolymers with 55 or 86% of BA units were also insufficient modifiers. The addition of the former yielded cured resins with homogeneous structure, whereas that of the latter resulted in macroscopic phase separation between the rubber and the epoxy resin.     

Effect of matrix ductility on the fracture behavior of rubber toughened epoxy resins

This paper investigates the effect of matrix ductility on toughness in a carboxyl-terminated butadiene-acryionitrile copolymer (CTBN) toughened diglycidyl ether of bisphenol-A (DGEBA)-piperidine system. Two kinds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4′-diaminodiphenol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrix T_g was significantly changed, but without alteration of the microstructure of the dispersed rubbery phase. The result of fracture energy tests reveals that the toughness of the neat epoxy resins increases slightly with the increase in the resin ductility. The toughness of the rubber-modified epoxy resins increases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size of the plastic deformation zone under constant rubbery-phase morphology is determined by the multiple but localized plastic shear yielding. Increasing matrix ductility increases the size of the plastic deformation zone by inducing more extensive shear yielding. In addition, fracture surfaces reveal that as the matrix rigidity is increased, an increasing proportion of the fracture energy is dissipated by rubber cavitation during crack initiation.     

Photodegradable polymers. II. Preparation of styrene copolymers with alkyl and phenyl β-styryl ketones and their photodegradability

Photodegradable polymers having pendent carbonyl groups attached directly to the polymer chain were prepared by copolymerization of styrene (St) with alkyl and phenyl β-styryl ketones (RCOCH?CHC₆H₅), where R = CH₃, C₂H₅, n-C₅H₁₁, n-C₁₁H₂₃, t-C₄H₉, cyclo-C₆H₁₁, and C₆H₅. The photodegradability of these copolymers was traced by viscometric and IR spectroscopic measurements. The degradability of St–benzalacetophenone (BAPh) copolymer is greater than that of St–alkyl styryl ketone copolymers under the irradiation of a high-pressure Hg lamp. The photodecomposition behavior St–BAPh copolymer was investigated in detail by a spectoirradiation technique. The changes in molecular weight and its distribution by photodegradation were measured by gel permeation chromatography, and the quantum yield for bond scission along the main chains of the copolymer was estimated to be about 5 × 10^?3 by 328 nm irradiation in a benzene solution. Examination of the effect of wavelength of the radiation on the bond scission showed that 328-nm light is most effective. The photochemical degradation process was shown to occur chiefly via triplet state of carbonyl groups by the quenching technique using 1,3-cyclohexadiene as a triplet quencher. The quantum yield of decarbonylation process was also estimated to be about 4.2 × 10 ^?2 in benzene.     

The Influence of the Alkyl Chain Length and Steric Effect on Stability Constants and Extractability of Co(II) Complexes with 1‐Alkyl‐4(5)‐methylimidazoles

Abstract

Extraction of Co(II) complexes has been studied with nine derivatives of 1‐alkyl‐4(5)‐methylimidazoles (with R=C₂H₃ to C₁₀H₂₁) from aqueous solution [I=0.5(KNO₃) at 25°C] with toluene, trichloromethane, and 2‐ethyl‐1‐hexanol. Stability constants of the complexes formed in the aqueous phase (β _c ) as well as partition constants (P _c ) of the extracted species were determined. It was demonstrated that both the stability constants and partition constants of the complexes increase with an increasing of the 1‐alkyl chain length. The tetrahedral together with octahedral complexes were formed beginning from the second step of complexation. Furthermore, the influence of the bulkiness of the 1‐alkyl group on separation process of Co(II) from Zn(II) for extractions with toluene and 2‐ethyl‐1‐hexanol were determined.     

Improving the toughness of epoxy with a reactive tetrablock copolymer containing maleic anhydride

Reactive block copolymers (BCPs) provide a unique means for toughening epoxy thermosets because covalent linkages provide opportunities for greater improvement in the fracture toughness (K_IC). In this study, a tailored reactive tetrablock copolymer, poly[styrene‐alt‐(maleic anhydride)]‐block‐polystyrene‐block‐poly(n‐butyl acrylate)‐block‐polystyrene, was incorporated into a diglycidyl ether of bisphenol A based epoxy resin. The results demonstrate the advantage of reactive BCP in finely tuning and controlling the structure of epoxy blends, even with 95 wt % epoxy‐immiscible triblocks. The size of the dispersed phase was efficiently reduced to submicrometer level. The mechanical properties, such as K_IC, of these cured blends were investigated. The addition of 10 wt % reactive BCP into the epoxy resins led to considerable improvements in the toughness, imparting nearly a 70% increase in K_IC. The designed reactive tetrablock copolymer opened good prospects because of its potential novel applications in toughening modification of engineering polymer composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42826.     

The Influence of Alkyl Chain Length and Steric Effect on Extraction of Zinc(II) Complexes with 1‐Alkyl‐2‐Methylimidazoles

Abstract

The extraction of Zn(II) complexes with six 1‐alkyl‐2‐methylimidazoles (alkyl is from C₅H₁₁ up to C₁₂H₂₅) from nitric solution was studied as a function of pH of the aqueous phase. As the organic solvents toluene, p‐xylene and 1,2,3,4‐tetrahydronaphthalene were used. The stability constants of the complexes in the aqueous phase as well as partition constants of the extractable species were determined. It was demonstrated that both the stability constants (β_c) and the partition constants (P_c) of the complexes increased with increasing alkyl chain length. Pseudo‐tetrahedral complexes were found to dominate at the second and third complexation steps, thus increasing the stability constants and facilitating extraction of the Zn(II) complexes with 1‐alkyl‐2‐methylimidazoles.     

Non-reactive and reactive block copolymers for toughening of UV-cured epoxy coating

Reactive and non-reactive diblock copolymers based on polyethylene oxide (PEO) and a poly(glycidyl methacrylate) (PGMA, reactive) or polystyrene (non-reactive) block, respectively, are prepared via ATRP and those are incorporated into a cycloaliphatic epoxy matrix. Crosslinking of the matrix is then performed by cationic UV curing, producing modified thermosets. ¹H NMR and SEC measurements are carried out and used to analyze the composition, the molar mass and dispersity of the prepared block copolymers. The viscoelastic properties and morphology of the modified epoxy are determined using DMTA and FESEM, respectively. The addition of 4 and 8 wt% of the reactive PEO-b-PGMA block copolymer into epoxy resin has only minor effects on the glass transition temperature, T_g. The reactive homopolymer PGMA significantly increases and the non-reactive block copolymer PEO-b-PS slightly decreases the glass transition temperature of the epoxy matrix. The non-reactive block copolymer PEO-b-PS causes a little decrease in T_g values. The measurement of the critical stress factor, K_IC, shows that the fracture toughness of the composite materials is enhanced by inclusion of the non-reactive block copolymer. In contrary, the reactive block copolymer has negative effect on the fracture toughness especially in case of short PEO block. FESEM micrographs studies on the fracture surfaces sustain the microphase separation and the increase in surface roughness in the toughened samples, indicating more energy was dissipated.     

Imidazole and chromium acetylacetonate as additives for the cure and fracture toughness of epoxy resins and their composites

The effects of additives such as 2-undecyl-imidazole (C₁₁Z) and chromium acetylacetonate (Cr(acac)₃) were examined on the curing behavior and fracture toughness of tetraglycidyldiaminodiphenyl methane/diaminodiphenyl sulphone (TGDDM/DDS) epoxy resins and their composites. The C₁₁Z additive alone reacted with TGDDM epoxy resins at about 127°C and increased the resin viscosity, resulting in an acceptable resin content for composite processing. Further addition of Cr(acac)₃ to TGDDM/DDS/C₁₁Z formulation increased the fracture toughness 5.7 times compared to the typical TGDDM/DDS/BF₃MEA epoxy formulation used for the preparation of laminates. The interlaminar fracture toughness of the laminates prepared by TGDDM/DDS/C₁₁Z/Cr(acac)₃ formulation was only twice as much as that prepared by typical TGDDM/DDS/BF₃MEA. This was due to the fiber bridging contribution to the interlaminar fracture toughness. Based on the experiment, this fiber bridging contribution was only dependent on the fiber content. Thus, the interlaminar fracture toughness is approximated by the sum of the fracture toughness of epoxy matrix and the estimated fiber bridging contribution.     

Studies on the curing behavior,thermal, and mechanical properties of epoxy resin-co-amine-functionalized lead phthalocyanine

A high performance copolymer was prepared by using epoxy (EP) resin as matrix and 3,10,17,24-tetra-aminoethoxy lead phthalocyanine (APbPc) as additive with dicyandiamide as curing agent. Fourier-transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TGA) were used to study the curing behavior, curing kinetics, dynamic mechanical properties, impact and tensile strength, and thermal stability of EP/APbPc blends. The experimental results show that APbPc, as a synergistic curing agent, can effectively reduce the curing temperature of epoxy resin. The curing kinetics of the copolymer was investigated by non-isothermal DSC to determine kinetic data and measurement of the activation energy. DMA, impact, and tensile strength tests proved that phthalocyanine can significantly improve the toughness and stiffness of epoxy resin. Highest values were seen on the 20 wt% loading of APbPc in the copolymers, energy storage modulus, and impact strength increased respectively 388.46 MPa and 3.6 kJ/m², T_g decreased 19.46°C. TGA curves indicated that the cured copolymers also exhibit excellent thermal properties.     

Toughening of aromatic diamine-cured epoxy resins by modification with hybrid modifiers composed of N-phenylmaleimide–styrene copolymers and N-phenylmaleimide–styrene–p-hydroxystyrene terpolymers

Hybrid modifiers composed of N-phenylmaleimide–styrene copolymers (PMS), and N-phenylmaleimide–styrene–p-hydroxystyrene terpolymers (PMSH) containing pendent p-hydroxyphenyl groups as functionalities, were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulphone. The hybrid modifiers were effective in toughening the epoxy resin. When using the modifier composed of 10 wt% PMS (M?_w 313000) and 2.5 wt% PMSH (2.5 mol% p-hydroxystyrene units, M?_w 316000), the fracture toughness (K_IC) for the modified resins increased 100% with no deterioration in the flexural properties and the glass transition temperature. The improvement in toughness of the epoxy resins was attained because of the co-continuous phase structure and the improvement in interfacial adhesion. The toughening mechanism is discussed in terms of the morphological characteristics of the modified epoxy resin systems.     

Preparation of highly dispersed gold nanoparticles inside the porous support assisted by amphiphilic vinyl maleate copolymer

An amphiphilic copolymer composed of maleic acid and alkyl (C₁₈) vinyl monomer was encapsulated into the porous support. A series of colloidal gold nanoparticles of known size was substantially immobilized in the composite porous supports based on cross-linked polyacrylate ester and cross-linked polystyrene resin. Maleic acid moiety of the amphiphilic copolymer can act as a stabilizer for gold nanoparticles in analogy to citric acid, whereas alkyl chains play a role for the stable accommodation of the amphiphilic copolymer. Maleic acid stabilizes the gold nanoparticles by flexing the geometrical arrangement of the linear polymer. Presence of C₁₈ alkyl chain in the poly(C₁₈-vinyl maleate) is indispensable to act as spacing group that prevents mutual aggregation of gold nanoparticles. On the other hand, gold nanoparticles with average diameter of less than 8 nm were spontaneously formed by treatment of the composite resin beads with aqueous HAuCl₄ solution, subsequently dispersed inside the pores of resin beads as observed by TEM. We have also elucidated the catalytic activity of the material with the hydrogenation of cinnamaldehyde in supercritical carbon dioxide. Notably, apparent size effect of gold was observed in the selectivity of the reaction.     

Nano-phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. PMMA-b-PnBA-b-PMMA triblock copolymers synthesized by living anionic polymerization were applied as the toughening modifiers for the epoxy resins. An aromatic amine, an acid anhydride and an anionic polymerization catalyst as curing agents resulted in macro-phase separation in the epoxy/triblock copolymer blends during the cure process. However, a phenol novolac as the curing agent created nano-phase structures in the epoxy blends. The size of the spherical phases or cylindrical phases was about 40 nm in diameter, and the main component in the nano-phases was the PnBA of the triblock copolymer. The fracture toughness of the epoxy/triblock copolymer alloys with the nano-cylindrical phases reached 2530 J/m². The fracture toughness was more than twenty fold relative to the unmodified epoxy resin, and was equivalent to the toughness of polycarbonates.     

Rapid crack propagation and arrest in polymers

Published results on dynamic fracture toughness vs crack velocity relations of polyester resin (Homalite-100), epoxy resin Araldite-B, modified epoxy resins and polycarbonate are reviewed. Commonality between the seemingly diversified experimental results as well as the existences of minimum dynamic fracture toughness, K_Im, and crack arrest stress intensity factor, K_Ia, as inherent material properties are discussed.     

Synthesis and mesophase behaviors of 2,5-disubstituted styrene-based random copolymers: Effect of difference in side-group length on liquid crystallinity

Five series of binary copolymers, poly[2,5-di(ROOC)styrene-co-2,5-di(R′OOC)styrene]s (R = n-C₃H₇-, R′ = C₂H₅-, n-C₄H₉-, and n-C₅H₁₁-; R = n-C₆H₁₃-, R′ = n-C₄H₉-, and n-C₅H₁₁-), were synthesized via free radical polymerization. The random nature of the copolymers was expected on the basis of the assumed similar reactivities of the analogous monomers and proved by ¹³C NMR analysis. It was also implied by the smoothly varying glass transition temperatures and further supported by the monotonous variation in d spacings for the liquid crystalline copolymers, where both corresponding homopolymers are liquid crystals. Subtle difference of R and R′ was found to have significant impact on the mesomorphic properties of the copolymers. When the pair of the corresponding homopolymers has the same mesogenic structure, a difference of one carbon atom in the alkyl chain can be tolerated over the whole copolymer composition range; however, the liquid crystalline structure soon disappears with the incorporation of a co-unit of an homopolymer that is not liquid crystal. For the copolymers with alkyl chain length differing by two carbon atoms, the liquid crystalline structure is lost with the incorporation of relatively low co-unit content despite the pair of corresponding homopolymers having the same mesogenic structure.     

Toughening of epoxy resin using synthesized polyurethane prepolymer based on hydroxyl-terminated polyesters

Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by a relatively low toughness. One approach to improve epoxy resin toughness includes the addition of either a rigid phase or a rubbery phase. A more recent approach to toughen brittle polymers is through interpenetrating network (IPN) grafting. It has been found that the mechanical properties of polymer materials with an IPN structure are fairly superior to those of ordinary polymers. Therefore, the present work deals with epoxy resin toughening using a polyurethane (PU) prepolymer as modifier via IPN grafting. For this purpose, a PU prepolymer based on hydroxyl-terminated polyester has been synthesized and used as a modifier at different concentrations. First, the PU-based hydroxyl-terminated polyester has been characterized. Next, an IPN (Epoxy–PU) has been prepared and characterized using Fourier transform infrared (FTIR) spectroscopy, thin-layer chromatography (TLC), and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. In this study, a Desmophen 1200-based PU prepolymer was used as a modifier at different concentrations within the epoxy resin. The results also showed that, further to the IPN formation, the epoxy and the PU prepolymer reacted chemically (via grafting). Compared to virgin resin, the effect on the mechanical properties was minor. The impact strength varies from 3–9 J/m and K_c from 0.9–1.2 MPa m^1/2. Furthermore, the incorporation of a chain extender with the PU prepolymer as a modifier into the mixture caused a drastic improvement in toughness. The impact strength increases continuously and reaches a maximum value (seven-fold that of virgin resin) at a modifier critical concentration (40 phr). K_c reaches 2.5 MPa m^1/2 compared to 0.9 MPa m^1/2 of the virgin resin. Finally, the SEM analysis results suggested that internal cavitation of the modifier particles followed by localized plastics shear yielding is probably the prevailing toughening mechanism for the epoxy resin considered in the present study. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2603–2618, 1998     

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