Degradable and chemically recyclable epoxy resins containing acetal linkages: Synthesis,properties, and application for carbon fiber‐reinforced plastics

Four sorts of epoxy resins containing degradable acetal linkages were synthesized by the reaction of bisphenol A (BA) or cresol novolak (CN) resin with vinyl ethers containing a glycidyl group [4‐vinlyoxybutyl glycidyl ether (VBGE) and cyclohexane dimethanol vinyl glycidyl ether (CHDMVG)] and cured with known typical amine‐curing agents. The thermal and mechanical properties of the cured resins were investigated. Among the four cured epoxy resins, the CN‐CHDMVG resin (derived from CN and CHDMVE) exhibited relatively high glass transition temperature (T_g = ca. 110 °C). The treatment of these cured epoxy resins with aqueous HCl in tetrahydrofuran (THF) at room temperature for 12 h generated BA and CN as degradation main products in high yield. Carbon fiber‐reinforced plastics (CFRPs) were prepared by heating the laminated prepreg sheets with BA‐CHDMVG (derived from BA and CHDMVE) and CN‐CHDMVG, in which strands of carbon fibers are impregnated with the epoxy resins containing conventional curing agents and curing accelerators. The obtained CFRPs showed good appearance and underwent smooth breakdown with the aqueous acid treatment in THF at room temperature for 24 h to produce strands of carbon fiber without damaging their surface conditions and tensile strength. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel photocurable monomers: The synthesis of difunctional vinyl ethers with a phosphonate group and difunctional 1‐propenyl ethers with a phosphonate group and their photoinitiated cationic polymerization

Phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were prepared by the regioselective addition reaction of glycidyl vinyl ether (GVE) or 1‐propenyl glycidyl ether with diaryl phosphonates with quaternary onium salts as catalysts. The reaction of GVE with bis(4‐chlorophenyl) phenylphosphonate gave bis[1‐(4‐chlorophenoxy methyl)‐2‐(vinyloxy)ethyl]phenylphosphonate in a 68% yield. The structures of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were confirmed by IR and ¹H NMR spectra and elemental analysis. Photoinitiated cationic polymerizations of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were investigated with photoacid generators. The polymerization of vinyl ether groups and 1‐propenyl ether groups of the obtained monomers proceeded very smoothly with a sulfonium‐type cationic photoinitiator, bis[4‐(diphenylsulfonio)phenyl]sulfide‐bis(hexafluorophosphate), upon UV irradiation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3105–3115, 2005     

Synthesis of phosphorus‐containing vinyl ether monomers and oligomers and their photoinitiated polymerization

Divinyl ether monomers containing phosphorous residues were synthesized by the addition reaction of glycidyl vinyl ether (GVE) with various phosphonic dichlorides or dichlorophosphates with quaternary onium salts as catalysts. The reaction of GVE with phenylphosphonic dichloride gave bis[1‐(chloromethyl)‐2‐(vinyloxy)ethyl]phenylphosphonate ( 1a ) in a 77% yield. The polycondensation of 1a with terephthalic acid was also carried out with 1,8‐diazabicyclo[5.4.0]undecene‐7 (DBU) as a condensing agent to afford the corresponding phosphorus‐containing polyester. A multifunctional monomer containing both vinyl ether groups and methacrylate groups was prepared by the reaction of 1a with methacrylic acid with DBU. The photoinitiated cationic polymerization of these vinyl ether compounds proceeded rapidly with bis[4‐(diphenylsulfonio)phenyl]sulfide‐bishexafluorophosphate as the cationic photoinitiator without a solvent upon ultraviolet irradiation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2031–2042, 2004     

Photoinitiated curing of mono‐ and bifunctional epoxides by combination of active chain end and activated monomer cationic polymerization methods

Photoinitiated cationic polymerization of mono‐ and bifunctional epoxy monomers, namely cyclohexeneoxide (CHO), 4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexanecarboxylate (EEC), respectively by using sulphonium salts in the presence of hydroxylbutyl vinyl ether (HBVE) was studied. The real‐time FTIR spectroscopic, gel content determination, and thermal characterization studies revealed that both hydroxyl and vinyl ether functionalities of HBVE take part in the polymerization. During the polymerization, HBVE has the ability to react via both active chain end (ACE) and activated monomer mechanisms through its hydroxyl and vinyl ether functionalities, respectively. Thus, more efficient curing was observed with the addition of HBVE into EEC‐containing formulations. It was also demonstrated that HBVE is effective in facilitating the photoinduced crosslinking of monofunctional epoxy monomer, CHO in the absence of a conventional crosslinker. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4914–4920, 2007     

Synthesis and radical polymerization of styrene‐based monomer having a five‐membered cyclic carbonate structure

A styrene‐based monomer having a five‐membered cyclic carbonate structure, 4‐vinylbenzyl 2,5‐dioxoran‐3‐ylmethyl ether (VBCE), was prepared by lithium bromide‐catalyzed addition of carbon dioxide to 4‐vinylbenxyl glycidyl ether (VBGE). Radical polymerization of the obtained VBCE was carried out using 2,2′‐azobisisobutyronitrile as an initiator. PolyVBCE with number‐averaged molecular weight higher than 13,800 was obtained by a solution polymerization in N,N‐dimethylformamide, N,N‐dimethylacetamide, dimethyl sulfoxide, and methyl ethyl ketone. The glass transition temperature and 5 wt % decomposition temperature of the polyVBCE were determined to be 52 and 305 °C by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBCE repeating unit can be also obtained via chemical modification of polyVBGE, that is, a lithium‐bromide‐catalyzed addition of carbon dioxide to a polyVBGE prepared from a radical polymerization of VBGE. Further copolymerization of VBCE with styrene gave the corresponding copolymer in a high yield. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of internal mold release agent on flexural and inter laminar shear properties of carbon and glass fabric reinforced thermoset composites

The study is focused on thermoset composites reinforced with carbon and glass woven fabrics. Two types of thermoset resins, for example, epoxy and vinyl ester were used as the matrix. Varying concentrations of internal mold releasing (IMR) agent was used in the resin. The composites were cured both at room temperature and at 80°C. The flexural properties were studied using 3‐point bending test method. Further theinter‐laminar shear strength (ILSS) was investigated using the short beam shear strength test based on 3‐point bending. The flexural modulus of room temperature cured epoxy resin is higher than that of high temperature cured epoxy resin and cured vinyl ester resin. The flexural modulus is lowest for 1% IMR sample in epoxy system and the modulus for 0% and 2% epoxy are not significantly different. Lowest flexural strength and modulus can be observed for the combination of reinforcement and curing conditions for samples containing 1% IMR for the epoxy systems. Carbon fiber is found to be less compatible with the vinyl ester resin system and the addition of IMR to the resin degraded the properties further. Inter‐laminar shear strength for epoxy‐based composites is not much affected by presence of IMR, but in case of vinyl ester based composites there is a decrease in ILSS on addition of IMR agent. The study explains variation in flexural properties on addition of IMR and change of curing conditions. These results can be used for ascertaining variation in mechanical properties in real use.     

Miscibility and morphologies of poly(arylene ether phenyl phosphine oxide/sulfone) copolymer/vinyl ester resin mixtures and their cured networks

Nonreactive bisphenol A‐based poly(arylene ether triphenyl phosphine oxide/diphenyl sulfone) statistical copolymers and a poly(arylene ether triphenyl phosphine oxide) homopolymer, each having a number‐average molecular weight of about 20 kg/mol, were synthesized and solution‐blended with a commercial dimethacrylate vinyl ester resin. Free‐radical cured systems produced morphologies that were a function of both the amount of phosphonyl groups and the weight percentage of the copolymers. For example, highly hydrogen‐bonded poly(arylene ether phenyl phosphine oxide) homopolymer/vinyl ester resin mixtures were homogeneous in all proportions both before and after the formation of networks. Copolymers containing low amounts (≤30 mol %) of the phosphonyl groups displayed phase separation either before or during cure. The phase‐separated cured materials generally had phase‐inverted morphologies, such as a continuous thermoplastic copolymer phase and a particulate, discontinuous vinyl ester network phase, except for systems containing a very low copolymer content. The resin modified with a copolymer containing 30 mol % phosphine oxide comonomer showed improved fracture toughness, suggesting the importance of both phase separation and good adhesion between the thermoplastic polymer and the crosslinked vinyl ester filler phase. The results suggested that the copolymers with high amounts of phosphine oxide should be good candidates for interphase sizing materials between a vinyl ester matrix and high‐modulus carbon fibers for advanced composite systems. Copolymers with low amounts of phosphonyl groups can produce tough, vinyl ester‐reinforced plastics. The char yield increases with the concentration of bisphenol A poly(arylene ether phosphine oxide) content, suggesting enhanced fire resistance. The incorporation of thermoplastic copolymers sustains a high glass‐transition temperature but does not significantly affect the thermal degradation onset temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2409–2421, 2000     

Synthesis and properties of biobased epoxy resins. part 1. Glycidylation of flavonoids by epichlorohydrin

Biobased epoxy resins were synthesized from a catechin molecule, one of the repetitive units in natural flavonoid biopolymers also named condensed tannins. The reactivity of catechin toward epichlorohydrin to form glycidyl ether derivatives was studied using two model compounds, resorcinol and 4‐methylcatechol, which represent the A and B rings of catechin, respectively. These model molecules clearly showed differences in reactivity upon glycidylation, explaining the results found with catechin monomer. The reaction products were characterized by both FTIR and NMR spectroscopy and chemical assay. The glycidyl ether of catechin (GEC) was successfully cured in various epoxy resin formulations. The GECs thermal properties showed that these new synthesized epoxy resins displayed interesting properties compared to the commercial diglycidyl ether of bisphenol A (DGEBA). For instance, when incorporated up to 50% into the DGEBA resin, GEC did not modify the glass‐transition temperature. Epoxy resins formulated with GEC had slightly lower storage moduli but induced a decrease of the swelling percentage, suggesting that GEC‐enhanced crosslinking in the epoxy resin networks. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and radical polymerization of styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure

A styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure, 4‐vinylbenzyl 1,3‐oxathiolane‐2‐thione‐5‐ylmethyl ether (VBTE), was synthesized from 4‐vinylbenzyl glycidyl ether (VBGE) and carbon disulfide in the presence of lithium bromide in 86% yield. Radical polymerization of VBTE in dimethyl sulfoxide by 2,2′‐azobisisobutyronitrile was carried out at 60 °C to afford the corresponding the polymer, polyVBTE, in 64% yield. PolyVBTE with number‐averaged molecular weight higher than 31,000 was obtained. The glass transition temperature (T_g) and 5 wt % decomposition temperature (T_d5) of the polyVBTE were evaluated to be 66 and 264 °C under nitrogen atmosphere by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBTE repeating unit could also be obtained via polymer reaction, that is, a lithium bromide‐catalyzed addition of carbon disulfide to a polyVBGE prepared from a radical polymerization of VBGE. Copolymerization of VBTE and styrene with various compositions efficiently gave copolymers of VBTE and styrene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Role of cyclic dithiocarbonate as a promoter in the reaction of epoxide and imine in the presence of water

It was demonstrated that the reaction of epoxide and imine as a latent initiator under highly humid conditions was accelerated by addition of 5‐phenoxymethyl‐1,3‐oxathiolane‐2‐thione ( 1 ). When 1 was added to a mixture of glycidyl phenyl ether and an imine, the reaction of the epoxide with an amine released from the imine became faster than was the case without 1 , that is, 1 worked as a promoter of the reaction. The curing rate and initial adhesive strength of epoxy resin increased compared with that without 1 . © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4276–4283, 2004     

Synthesis of raspberry-like monodisperse magnetic hollow hybrid nanospheres by coating polystyrene template with Fe(3)O(4)@SiO(2) particles

A new inorganic/organic hybrid material containing silsesquioxane was prepared by the reaction of caged octa (aminopropyl silsesquioxane) (POSS-NH(2)) with n-butyl glycidyl ether (nBGE) and 1,4-butanediol diglycidyl ether (BDGE). The copolymers of POSS, nBGE, and BDGE could be obtained with varied feed ratio of POSS-NH(2), nBGE, and BDGE in the preparation. The hybrid material was added into an epoxy resin (E51) for enhancing the toughening and thermal properties of the epoxy resin. The results showed that the toughening and the thermal properties of the cured epoxy resin were greatly improved by the addition of the hybrid. The enhancement was ascribed to nano-scale effect of the POSS structure and the formation of anchor structure in the cured network. The investigation of kinetics for the curing process of the hybrid-modified epoxy resin revealed that two kinds of curing reactions occurred in different temperature ranges. They were attributed to the reactions between amino groups of the curing agent with epoxy groups of E51 and with residue epoxy groups in the hybrid. The reacting activation energies were calculated based on Kissinger's and Flynn-Wall-Ozawa's methods, respectively.     

Preparation and properties of biocomposites composed of bio‐based epoxy resin,tannic acid,and microfibrillated cellulose

As new bio‐based epoxy resin systems, glycerol polyglycidyl ether (GPE) and sorbitol polyglycidyl ether (SPE) were cured with tannic acid (TA) at various conditions. When the curing conditions were optimized for the improvement of thermal and mechanical properties, the most balanced properties were obtained for the GPE/TA and SPE/TA cured at 160 °C for 2–3 h at the epoxy/hydroxyl ratio of 1/1. The cured SPE/TA had a higher glass transition temperature (T_g) and tensile strength than the cured GPE/TA. Next, biocomposites of GPE/TA and SPE/TA with microfibrillated cellulose (MFC) were prepared by mixing aqueous solution of the epoxy/curing reagent with MFC, and subsequent drying and curing at the optimized condition. For both the GPE/TA/MFC and SPE/TA/MFC biocomposites, T_g and the storage modulus at rubbery plateau region increased with increasing MFC content over the studied range of 3–15 wt %. The tensile strength at 25 °C for GPE/TA/MFC biocomposite with MFC content 10 wt % was 76% higher than that of control GPE/TA, while the tensile modulus was little improved. On the other hand, the tensile strength and modulus of SPE/TA/MFC biocomposite with MFC content 10 wt % were 30 and 55% higher than those of control SPE/TA, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 425–433, 2010     

Fracture toughening of epoxy matrices with blends of resins of different molecular weights and other modifiers

The microstructure and fracture behavior of epoxy mixtures containing two monomers of different molecular weights were studied. The variation of the fracture toughness by the addition of other modifiers was also investigated. Several amounts of high‐molecular‐weight diglycidyl ether of bisphenol A (DGEBA) oligomer were added to a nearly pure DGEBA monomer. The mixtures were cured with an aromatic amine, showing phase separation after curing. The curing behavior of the epoxy mixtures was investigated with thermal measurements. A significant enhancement of the fracture toughness was accompanied by slight increases in both the rigidity and strength of the mixtures that corresponded to the content of the high‐molecular‐weight epoxy resin. Dynamic mechanical and atomic force microscopy measurements indicated that the generated two‐phase morphology was a function of the content of the epoxy resin added. The influence of the addition of an oligomer or a thermoplastic on the morphologies and mechanical properties of both epoxy‐containing mixtures was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3920–3933, 2004     

Synthesis of poly(vinyl ether)‐based,ABA triblock‐type thermoplastic elastomers with functionalized soft segments and their gas permeability

The ABA‐type triblock copolymers consisting of poly(2‐adamantyl vinyl ether) [poly(2‐AdVE)] as outer hard segments and poly(6‐acetoxyhexyl vinyl ether) [poly(AcHVE)], poly(6‐hydroxyhexyl vinyl ether) [poly(HHVE)], or poly(2‐(2‐methoxyethoxy)ethyl vinyl ether) [poly(MOEOVE)] as inner soft segments were synthesized by sequential living cationic polymerization. Despite the presence of polar functional groups such as ester, hydroxyl, and oxyethylene units in their soft segments, the block copolymers formed elastomeric films. The thermal and mechanical properties and morphology of the block copolymers showed that the two polymer segments of these triblock copolymers were segregated into microphase‐separated structure. Effect of the functional groups in the soft segments on gas permeability was investigated as one of the characteristics of the new functional thermoplastic elastomers composed solely of poly(vinyl ether) backbones. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1114–1124     

Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocomposites

Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol‐A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF₃MEA). BF₃MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and ²⁹Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF₃MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4′‐diaminodiphenysulfone (DDS). The thermal‐cured epoxy–nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA–DDS–BF₃MEA‐cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS‐cured epoxy–nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757–768, 2006     

Block copolymer modified novolac epoxy resin

The phase behavior of uncured and cured mixtures containing stoichiometric amounts of Epon164 novolac epoxy resin and 4,4′‐methylenedianiline combined with a nearly symmetric poly(methyl acrylate‐co‐glycidyl methacrylate‐b‐polyisoprene) diblock copolymer was investigated with small‐angle X‐ray scattering and transmission electron microscopy. A series of morphologies were documented as a function of the copolymer concentration, which ranged from pure diblock to 2.5 wt % in the thermoset resin. Ordered lamellae bordered a wide multiphase region followed by disordered wormlike micelles that transformed continuously into vesicles at the lowest compositions. The thermal curing of this pentafunctional epoxy system to complete conversion had little impact on the phase behavior of the mixtures, and this was consistent with previous experiments with difunctional epoxy and the same hardening agent. However, changing the epoxy component led to gross changes in the phase behavior that were interpreted with the concept of a wet‐to‐dry brush transition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1994–2003, 2003     

Factors influencing EB curing of epoxy matrix

The effectiveness of electron beam (EB) curing of epoxy resins was found to be influenced by catalyst. In the presence of iodonium salt (diaryl iodonium hexafluoroantimonate, C3), the EB curing of epoxy resin is easier than in the presence of triaryl sulfonium hexafluoroantimonate (C1), or triaryl sulfonium hexafluorophosphate (C2), or iron arene containing cationic catalyst (Irgacure 261). The epoxy 616 (diglycidyl ether of bisphenol A) and 648 (diglycidyl ether of phenolic novolacs) can be cured by the above onium salts catalysts C1–C3. The epoxy with glycidyl amino epoxide group (such as AG 80; AFG 90) could not be cured by onium salts catalyst. The influence of irradiation dose, temperature and the effect of impurities on curing reaction were investigated.     

Effect of low current density electrochemical oxidation on the properties of carbon fiber‐reinforced epoxy resin composites

Changes in surface physicochemical structures of polyacrylonitrile‐based carbon fibers resulted from low current density electrochemical oxidation were monitored by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The relationship between the interlaminar shear strength (ILSS) values of carbon fiber‐reinforced polymers (CFRPs) and carbon fiber surface chemistry including elemental ratios and the relative content of oxygen‐containing functional groups were researched. SEM results revealed that the electrochemical oxidation got rid of surface contaminants generated during the production process. XPS analysis showed that the relative contents of oxygen and nitrogen increased by 446% and 202%, respectively, after the electrochemical oxidation. Carbon fiber surface chemistry was of paramount importance to the interfacial properties of CFRPs. The higher the carbon fiber surface activity, the better the interfacial bonding was, and an increase in the acidic‐group contents was responsible for a higher ILSS value. However, when the current density increased to 1.0 A/m², the interfacial bonding between carbon fiber and the epoxy resin became weak which led to the decline in ILSS values. Copyright © 2012 John Wiley & Sons, Ltd.     

Diglycidyl ether of bisphenol‐A epoxy resin modified using poly(ether ether ketone) with pendent tert‐butyl groups

Bisphenol‐A‐based difunctional epoxy resin was modified with poly(ether ether ketone) with pendent tert‐butyl groups (PEEKT). PEEKT was synthesized by the nucleophilic substitution reaction of 4,4′‐difluoro benzophenone with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone. Blends with various amounts of PEEKT were prepared by melt‐mixing. All the blends were homogeneous in the uncured state. The glass transition temperature of the binary epoxy/PEEKT blends was predicted using several equations. Reaction‐induced phase separation was found to occur upon curing with a diamine 4,4′‐diaminodiphenyl sulfone. The phase morphology of the blends was studied using scanning electron microscopy. From the micrographs, it was found that PEEKT‐rich phase was dispersed in a continuous epoxy matrix. The domain size increased with the amount of PEEKT in the blends. The increase in domain size was due to the coalescence of the domains after phase separation. Dynamic mechanical analysis of the blends gave two peaks corresponding to epoxy‐rich phase and thermoplastic‐rich phase. The tensile strength and modulus of the blends remained close to that of the unmodified resin, while the flexural properties decreased with the addition of PEEKT to epoxy resin. The fracture toughness of the epoxy resin increased with the addition of PEEKT. Investigation of the fracture surfaces revealed evidences for local plastic deformation of the matrix, crack pinning, crack path deflection, and ductile tearing of PEEKT‐rich phase. Thermogravimetric analysis revealed that the initial decomposition temperature of the blends were close to that of the unmodified resin. Finally, the properties of the blends were compared with other modified PEEK/epoxy blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2481–2496, 2007     

Epoxy/amine‐functionalized short‐length vapor‐grown carbon nanofiber composites

Short length vapor‐grown carbon nanofibers (VGCNFs) were functionalized with 4‐aminobenzoic acid in polyphosphoric acid/phosphorous phentoxide medium via “direct” Friedel‐Crafts acylation reaction to afford aminobenzoyl‐functionalized VGCNFs (AF‐VGCNFs). The AF‐VGCNFs as a cocuring agent were mixed with epoxy resin by simple mechanical stirring in methanol which was added to help efficient mixing. After evaporation of methanol, 4,4′‐methylenedianiline as a curing agent was added to the mixture, which was then cured at elevated temperatures. The resultant composites displayed uniform dispersion of AF‐VGCNFs into cured epoxy matrix. During curing process, the amine functionalities on AF‐VGCNF together with 4,4′‐methylenedianiline were expected to be involved in covalent attachment to the epoxy resin. As a result, both tensile modulus and strength of the composites were improved when compared with those of pure epoxy resin. Thus, the AF‐VGCNFs play a role as an outstanding functional additive, which could resolve both dispersion and interfacial adhesion issues at the same time by functionalization of VGCNFs and covalent bonding between the additive and matrix, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7473–7482, 2008