Toughening of an epoxy resin with hydroxy‐terminated poly(arylene ether nitrile) with pendent tertiary butyl groups

Hydroxy‐terminated poly(arylene ether nitrile) oligomers with pendent tert‐butyl groups (PENTOH) were synthesized by the nucleophilic aromatic substitution reaction of 2,6‐dichlorobenzonitrile with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone medium with anhydrous potassium carbonate as a catalyst at 200°C in a nitrogen atmosphere. The PENTOH oligomers were blended with diglycidyl ether of bisphenol A epoxy resin and cured with 4,4′‐diaminodiphenyl sulfone. The curing reaction was monitored with infrared spectroscopy and differential scanning calorimetry. The morphology, fracture toughness, and thermomechanical properties of the blends were investigated. The scanning electron micrographs revealed a two‐phase morphology with a particulate structure of the PENTOH phase dispersed in the epoxy matrix, except for the epoxy resin modified with PENTOH with a number‐average molecular weight of approximately 4000. The storage modulus of the blends was higher than that of the neat epoxy resin. The crosslink density calculated from the storage modulus in the rubbery plateau region decreased with an increase in PENTOH in the blends. The fracture toughness increased more than twofold with the addition of PENTOH oligomers. The tensile strength of the blends increased marginally, whereas the flexural strength decreased marginally. The dispersed PENTOH initiated several toughening mechanisms, which improved the fracture toughness of the blends. The thermal stability of the epoxy resin was not affected by the addition of PENTOH to the epoxy resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Epoxy‐tert‐butyl poly(cyanoarylene ether) blends: Phase morphology,fracture toughness,and mechanical properties

Tert‐butyl hydroquinone–based poly(cyanoarylene ether) (PENT) was synthesized by the nucleophilic aromatic substitution reaction of 2,6‐dichlorobenzonitrile with tert‐butyl hydroquinone using N‐methyl‐2‐pyrrolidone (NMP) as solvent in the presence of anhydrous potassium carbonate in a nitrogen atmosphere at 200°C. PENT‐toughened diglycidyl ether of bisphenol A epoxy resin (DGEBA) was developed using 4,4′‐diaminodiphenyl sulfone (DDS) as the curing agent. Scanning electron micrographs revealed that all blends had a two‐phase morphology. The morphology changed from dispersed PENT to a cocontinuous structure with an increase in PENT content in the blends from 5 to 15 phr. The viscoelastic properties of the blends were investigated using dynamic mechanical thermal analysis. The storage modulus of the blends was less than that of the unmodified resin, whereas the loss modulus of the blends was higher than that of the neat epoxy. The tensile strength of the blends improved slightly, whereas flexural strength remained the same as that of the unmodified resin. Fracture toughness was found to increase with an increase in PENT content in the blends. Toughening mechanisms like local plastic deformation of the matrix, crack path deflection, crack pinning, ductile tearing of thermoplastic, and particle bridging were evident from the scanning electron micrographs of failed specimens from the fracture toughness measurements. The thermal stability of the blends were comparable to that of the neat resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3536–3544, 2006     

Cure kinetics, morphological and dynamic mechanical analysis of diglycidyl ether of bisphenol-A epoxy resin modified with hydroxyl terminated poly(ether ether ketone) containing pendent tertiary butyl groups

Hydroxyl terminated poly(ether ether ketone) based on tert-butyl hydroquinone (PEEKTOH) was used to modify a diglycidyl ether of bisphenol-A epoxy resin. A diamine, 4,4′-diaminodiphenylsulfone was used as the curing agent. Isothermal differential scanning calorimetric measurements of the blends were carried out at 180, 165 and 150 °C. The extent of reaction was found to decrease with the addition of PEEKTOH. The phenomenological model developed by Kamal was used for kinetic analysis of curing reaction. The curing reaction followed autocatalytic mechanism regardless of the presence and amount of oligomer present in the epoxy resin. The experimental and theoretical reaction rates were in good agreement during the initial stages of the reaction. The experimental values were lower than theoretical rate during the final stages of reaction due to increase in the viscosity of the system. A semiemperical model was used to explain diffusion control during final stages of reaction. The cured blends exhibited two phase morphology at all the curing temperatures. A uniform particle size distribution was observed at all compositions. The domain size decreased slightly with increase in oligomer content and with decrease in curing temperature. Finally, the viscoelastic properties were analysed using dynamic mechanical thermal analysis. Two T_gs corresponding to epoxy rich and thermoplastic rich phases were evident from the dynamic mechanical spectrum.     

Hydroxyl terminated poly(ether ether ketone) with pendent methyl group toughened epoxy resin: miscibility, morphology and mechanical properties

The synthesis, processing, thermal and mechanical properties and fracture toughness of epoxy resin formulated with hydroxyl terminated poly(ether ether ketone) with pendent methyl group are reported. Hydroxyl terminated poly(ether ether ketone) oligomers based on methyl hydroquinone (PEEKMOH) were synthesised from methylhydroquinone and 4,4′-difluorobenzophenone in N-methyl-2-pyrrolidone. PEEKMOH oligomers with different molecular weights were synthesised and characterised. Blends of diglycidyl ether of bisphenol-A epoxy resin with PEEKMOH were prepared by melt mixing. The uncured blends were homogeneous and the T_g-composition behaviour was predicted using Fox, Gordon–Taylor and Kelley–Bueche equations. Reaction induced phase separation occurred in the blends on curing with 4,4′-diaminodiphenyl sulfone. Scanning electron microscopy studies revealed the two-phase morphology of the blends. Domain size of the blends increased with increase in PEEKMOH8 in the blends. Phase separation in the blends occurred by nucleation and growth mechanism. Infrared spectroscopic studies revealed that some of the epoxy groups were opened up by hydroxyl group of PEEKMOH. The tensile and flexural properties of the blends were comparable to that of neat epoxy resin and the properties were dependent on the composition of the blend and molecular weight of PEEKMOH used. Dynamic mechanical analysis revealed two glass transition temperatures corresponding to epoxy rich and thermoplastic rich phases. The crosslink density of epoxy resin decreased with the addition of PEEKMOH to epoxy resin. The blends exhibited superior fracture toughness compared to unmodified epoxy resin. The increase in fracture toughness was due to local plastic deformation of the matrix, crack path deflection and crack pinning. The thermal stability of amine cured epoxy resin was not affected by the incorporation of PEEKMOH into the epoxy resin.     

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     

Toughening of Diglycidyl Ether of Bisphenol-A Epoxy Resin Using Poly (Ether Ether Ketone) with Pendent Ditert-Butyl Groups

Poly(ether ether ketone) (PEEKDT), hydroxyl terminated poly(ether ether ketone) (PEEKDTOH) and fluorine terminated poly (ether ether ketone) (PEEKDTF) with pendent ditert-butyl groups were synthesized by the nucleophilic substitution reaction of 4,4′-difluorobenzophenone with 2,5-ditert-butylhydroquinone in N-methyl-2-pyrrolidone medium using anhydrous potassium carbonate as catalyst. Diglycidyl ether of bisphenol-A epoxy resin was blended with PEEKDT, PEEKDTOH, and PEEKDTF, and cured with 4,4′-diaminodiphenylsulfone (DDS). The polymers formed heterogeneous blends before curing, and upon curing the polymers got dispersed in the epoxy matrix. The mechanical properties of the cured blends were slightly lower than that of the unmodified resin. The fracture toughness increased with the addition of ditert-butyl PEEK into epoxy resin and the extent of improvement was dependent on the type of modifier used. Hydroxyl terminated polymers gave up to 40% increase in fracture toughness. The dynamic mechanical spectrum of the blends showed only a single T_g due to the proximity of the glass transition temperature of modified PEEK and DDS cured epoxy resin.     

Hydroxyl terminated poly(ether ether ketone) with pendant methyl group‐toughened epoxy clay ternary nanocomposites: Preparation,morphology, and thermomechanical properties

Hydroxyl terminated poly(ether ether ketone) oligomer with pendant methyl group (PEEKMOH) was prepared. Ternary nanocomposites were processed by blending PEEKMOH oligomer with diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin along with organically modified montmorillonite (Cloisite 25A) followed by curing with 4,4'‐diamino diphenyl sulfone. Tensile moduli and flexural moduli were increased, while the tensile strength and Izod impact strength were decreased with increase in clay content. Similarly, storage moduli and loss moduli were increased and glass transition temperature was decreased as the percentage of clay increased. X‐ray diffractograms showed exfoliated morphology even with higher concentration of clay content (8 phr). Scanning electron microscopy of fractured surfaces and tensile failed specimens revealed slow crack propagation and increase in river markings with nanoclay incorporation confirming the improvement in toughness. The domain size of PEEKMOH was decreased with the incorporation of nanoclay into the epoxy matrix, indicating the restriction of growth mechanism by nucleation during phase separation. With increase in clay content, phase separation disappeared indicating gelation occurs before phase separation. Fracture toughness was increased with the addition of PEEKMOH and clay in epoxy resin. Coefficient of thermal expansion of nanocomposites decreases up to 3 phr clay concentrations thereafter it increases. A marginal increase in thermal stability was observed with increase in clay content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Epoxy resin containing the poly(sily ether): Preparation,morphology, and mechanical properties

The poly(sily ether) with pendant chloromethyl groups (PSE) was synthesized by the polyaddition of dichloromethylsilane (DCM) and diglycidylether of bisphenol A (DGEBA) with tetrabutylammonium chloride (TBAC) as a catalyst. This polymer was miscible with diglycidyl ether of bisphenol A (DGEBA), the precursor of epoxy resin. The miscibility is considered to be due mainly to entropy contribution because the molecular weight of DGEBA is quite low. The blends of epoxy resin with PSE were prepared through in situ curing reaction of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐diaminodiphenylmethane (DDM) in the presence of PSE. The DDM‐cured epoxy resin/PSE blends with PSE content up to 40 wt % were obtained. The reaction started from the initial homogeneous ternary mixture of DGEBA/DDM/PSE. With curing proceeding, phase separation induced by polymerization occurred. PSE was immiscible with the 4,4′‐diaminodiphenylmethane‐cured epoxy resin (ER) because the blends exhibited two separate glass transition temperatures (T_gs) as revealed by the means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). SEM showed that all the ER/PSE blends are heterogeneous. Depending on blend composition, the blends can display PSE‐ or epoxy‐dispersed morphologies, respectively. The mechanical test showed that the DDM‐cured ER/PSE blend containing 25 wt % PSE displayed a substantial improvement in Izod impact strength, i.e., epoxy resin was significantly toughened. The improvement in impact toughness corresponded to the formation of PSE‐dispersed phase structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 505–512, 2003     

Surface morphology,thermomechanical and barrier properties of poly(ether sulfone)‐toughened epoxy clay ternary nanocomposites

Poly(ether sulfone) (PES)‐toughened epoxy clay ternary nanocomposites were prepared by melt blending of PES with diglycidyl ether of bisphenol A epoxy resin along with Cloisite 30B followed by curing with 4,4′‐diaminodiphenylsulfone. The effect of organoclay and thermoplastic on the fracture toughness, permeability, viscoelasticity and thermomechanical properties of the epoxy system was investigated. A significant improvement in fracture toughness and modulus with reduced coefficient of thermal expansion (CTE) and gas permeability were observed with the addition of thermoplastic and clay to the epoxy system. Scanning electron microscopy of fracture‐failed specimens revealed crack path deflection and ductile fracture without phase separation. Oxygen gas permeability was reduced by 57% and fracture toughness was increased by 66% with the incorporation of 5 phr clay and 5 phr thermoplastic into the epoxy system. Optical transparency was retained even with high clay content. The addition of thermoplastic and organoclay to the epoxy system had a synergic effect on fracture toughness, modulus, CTE and barrier properties. Planetary ball‐milled samples gave exfoliated morphology with better thermomechanical properties compared to ultrasonicated samples with intercalated morphology. Copyright © 2010 Society of Chemical Industry     

Miscibility and mechanical properties of tetrafunctional epoxy resin/phenolphthalein poly(ether ether ketone) blends

Phenolphthalein poly(ether ether ketone) (PEK‐C) was found to be miscible with uncured tetraglycidyl 4,4′‐diaminodiphenylmethane (TGDDM), which is a type of tetrafunctional epoxy resin (ER), as shown by the existence of a single glass transition temperature (T_g) within the whole composition range. The miscibility between PEK‐C and TGDDM is considered to be due mainly to entropy contribution. Furthermore, blends of PEK‐C and TGDDM cured with 4,4′‐diaminodiphenylmethane (DDM) were studied using dynamic mechanical analysis (DMA), Fourier‐transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). DMA studies show that the DDM‐cured TGDDM/PEK‐C blends have only one T_g. SEM observation also confirmed that the blends were homogeneous. FTIR studies showed that the curing reaction is incomplete due to the high viscosity of PEK‐C. As the PEK‐C content increased, the tensile properties of the blends decreased slightly and the fracture toughness factor also showed a slight decreasing tendency, presumably due to the reduced crosslink density of the epoxy network. SEM observation of the fracture surfaces of fracture toughness test specimens showed the brittle nature of the fracture for the pure ER and its blends with PEK‐C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 598–607, 2001     

Epoxy toughening using low viscosity liquid diglycidyl ether of ethoxylated bisphenol‐A

Two new epoxy resins, diglycidyl ether of ethoxylated bisphenol‐A (BPA) with two and six oxyethylene units (DGEBAEO‐2 and DGEBAEO‐6) were synthesized and characterized. DGEBAEO‐6 was used to toughen the conventional epoxy resin diglycidyl ether of BPA (DGEBA). The blends of DGEBA with different amounts of DGEBAEO‐6 were cured by 4,4′‐diamino diphenylmethane (DDM), and their thermal and mechanical properties were examined. The DSC and DMA results presented that DGEBA/DGEBAEO‐6 blends exhibited a homogenous phase, and the glass transition temperature of the blends was inversely proportional to the content of DGEBAEO‐6. The impact strength of the cured blends was directly proportional to the content of DGEBAEO‐6, and reached five times higher than that of the neat DGEBA when 50 wt % DGEBAEO‐6 was used; the same impact strength was achieved for DDM‐cured DGEBAEO‐2. The viscosities of the blends decreased with increasing the DGEBAEO‐6 content, whereas the tensile and flexural strength and the thermal stabilities were not obviously affected. Scanning electron microscopic results confirmed that the plastic deformation inducing by the incorporated flexible oxyethylene units was responsible for the toughness improvement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of 4‐(4‐hydroxyphenoxy)phenol diglycidyl ether with improved toughness behavior

A high‐performance difunctional epoxy resin, 4‐(4‐hydroxyphenoxy)phenol diglycidyl ether (DHPOP), was synthesized by a two‐step method. The curing behavior of DHPOP was investigated by nonisothermal differential scanning calorimetry method and the curing kinetics results revealed that the introduction of ether linkage could improve the activity of epoxy groups, leading to a lower curing temperature and apparent activation energy compared with that of the commercial bisphenol‐A diglycidyl ether (DGEBA). A series of copolymers were then prepared by varying the mass ratio of DHPOP and DGEBA, which were cured with 4,4′‐diaminodiphenyl methane. The effect of DHPOP contents on thermal and mechanical properties and fracture morphology was studied. As expected, with the increase of DHPOP in the network, the impact strength and char yield were significantly enhanced, while the glass transition temperature (T_g) remained unchanged because of the increase of crosslink density. The excellent toughness endows the DHPOP with the promising potential for the application as high‐performance resin matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46458.     

Cure kinetics,phase behaviors,and fracture properties of bismaleimide resin toughened by poly(phthalazinone ether ketone)

Poly(phthalazinone ether ketone)s (PPEK) were used to toughen bismaleimide (BMI) resin composed of 4,4′‐bismaleimidodiphenyl methane (BMDM) and O,O′‐diallyl bisphenyl A (DABPA). Dynamic differential scanning calorimetry (DSC) of the blends was carried out for kinetic analysis of the curing reaction. The reaction activation energy indicated that the reaction mechanism remained the same even after the incorporation of PPEK. The reaction‐induced phase separation process in BMI/PPEK blends was investigated by optical microscopy (OM). The primary phase structure of the blends was fixed at the early stage of phase separation, and a secondary phase separation was observed as a result of the high viscosity of the blends. Scanning electron microscope (SEM) graphs showed that the morphology of the cured resin changed from a dispersed structure to a phase‐inverted structure with the increase of PPEK content. Compared with the neat resin, the fracture toughness of the modified resin exhibits a moderate increase when PPEK was incorporated. Several toughening mechanisms, such as local plastic deformation, crack deflection, and branches, presumably took part in improving the toughness of BMI/PPEK blends on the basis of the morphology. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Interaction and properties of epoxy‐amine system modified with poly(phthalazinone ether nitrile ketone)

An epoxy based on the tetraglycidyl 4,4′‐diaminodiphenyl‐ methane (TGDDM)/bisphenol A type novolac(F‐51) cured with 4,4′‐diaminidiphenysulfone (DDS) has been modified with Poly (phthalazinone ether nitrile ketone)(PPENK). The interaction between the PPENK and epoxy resin have been investigated by differential scanning calorimetry (DSC), FT‐IR, and dynamic mechanical analysis (DMA). The thermal and mechanical properties were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), flexural, impact strength, and the critical stress intensity factor tests. The results showed that a large number of physical crosslinks formed by intermolecular and intramolecular hydrogen bonding indeed existed in the TGDDM/F‐51/PPENK blends. These interactions gave good compatibility between PPENK and epoxy resin. So that any phase separation had not been detected by DMA and scanning electron microscope (SEM). Beyond that the interaction could also be a benefit to the thermal and mechanical properties. Compared with the neat epoxy resin, the critical stress intensity factor values reached the maximum at 10‐phr PPENK, as well as the impact strength. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42938.     

Reaction‐induced phase separation and resulting thermomechanical and surface properties of epoxy resin/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) blends cured with 4,4′‐diaminodiphenylsulfone

We investigated the phase separation, cure kinetics and thermomechanical properties of diglycidyl ether of bisphenol‐A/4,4′‐diaminodiphenylsulfone/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (TBCP) blends. Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy revealed that the blends exhibited heterogeneous phase morphology in which the TBCP formed dispersed domains in epoxy matrix, due to reaction induced phase separation. A fraction of phase‐separated PEO phase underwent partial crystallization whereas another fraction formed interphases between the dispersed domains and epoxy matrix. Moreover, the dispersed PEO chains improved the compatibility and interfacial adhesion between the matrix and domains and, consequently, significantly improved the mechanical properties of epoxy resin. Furthermore, the thermal degradation studies and contact angle measurements disclosed that the dispersed domains were well protected by the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44406.     

Phthalonitrile‐epoxy blends: Cure behavior and copolymer properties

Binary blends composed of 4,4′‐bis(3,4‐dicyanophenoxy)biphenyl (biphenyl PN) and diglycidyl ether of bisphenol A (epoxy resin) and oligomeric n = 4 phthalonitrile (n = 4 PN) and epoxy resin were prepared. The cure behavior of the blends was studied under dynamic and isothermal curing conditions using differential scanning calorimetry, simultaneous thermogravimetric/differential thermal analysis, infrared spectroscopy, and rheological analysis. The studies revealed that phthalonitrile‐epoxy blends exhibited good processability and that they copolymerized with or without the addition of curing additive. In the absence of curing additive, the blends required higher temperatures and longer cure times. The thermal and dynamic viscoelastic properties of amine‐cured phthalonitrile‐epoxy copolymers were examined and compared with those of the neat epoxy resin. The properties of the epoxy resin improved with increasing biphenyl PN content and with n = 4 PN addition. Specifically, the copolymers exhibited higher glass transition temperatures, increased thermal and thermo‐oxidative stabililty, and enhanced dynamic mechanical properties relative to the commercially available epoxy resin. The results showed that the phthalonitrile‐epoxy blends and copolymers have an attractive combination of processability and high temperature properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Toughening of epoxy resin by functional‐terminated polyurethanes and/or semicrystalline polymer powders

Hydroxyl‐, amine‐, and anhydride‐terminated polyurethane (PU) prepolymers, which were synthesized from polyether [poly(tetramethylene glycol)] diol, 4,4′‐diphenylmethane diisocyanate, and a coupling agent, bisphenol‐A (Bis‐A), 4,4′‐diaminodiphenyl sulphone (DDS), or benzophenonetetracarboxylic dianhydride, were used to modify the toughness of Bis‐A diglycidyl ether epoxy resin cured with DDS. Besides the crystalline polymers, poly(butylene terephthalate) (PBT) and poly(hexamethylene adipamide) (nylon 6,6), with particle sizes under 40 μm were employed to further enhance the toughness of PU‐modified epoxy at a low particle content. As shown by the experimental results, the modified resin displayed a significant improvement in fracture energy and also its interfacial shear strength with polyaramid fiber. The hydroxyl‐terminated PU was the most effective among the three prepolymers. The toughening mechanism is discussed based on the morphological and the dynamic mechanical behavior of the modified epoxy resin. Fractography of the specimen observed by the scanning electron microscopy revealed that the modified resin had a two‐phase structure. The fracture properties of PBT‐particle‐filled epoxy were better than those of nylon 6,6‐particle‐filled epoxy. Nevertheless, the toughening effect of these crystalline polymer particles was much less efficient than that of PU modification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2903–2912, 2001     

Curing behavior and thermal and mechanical properties enhancement of tetraglycidyl‐4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone using a liquid crystalline epoxy

A thermosetting resin system, based on tetraglycidyl‐4,4′‐diaminodiphenylmethane, has been developed via copolymerization with 4,4′‐diaminodiphenylsulfone in the presence of a newly synthesized liquid crystalline epoxy (LCE). The curing behavior of LCE‐containing resin system was evaluated using curing kinetics method and Fourier transform infrared spectroscopy. The effect of LCE on the thermal and mechanical properties of modified epoxy systems was studied. Thermogravimetric analysis indicated that the modified resin systems displayed a high T_0.05 and char yield at lower concentrations of LCE (≤5 wt%), suggesting an improved thermal stability. As determined using dynamic mechanical analysis and differential scanning calorimetry, the glass transition value increased by 9.7% compared to that of the neat resin when the LCE content was 5 wt%. Meanwhile, the addition of 5 wt% of LCE maximized the toughness with a 175% increase in impact strength. The analysis of fracture surfaces revealed a possible effect of LCE as a toughener and showed no phase separation in the modified resin system, which was also confirmed by dynamic mechanical analysis. © 2016 Society of Chemical Industry     

Preparation of poly(1,4‐cyclohexylenedimethylene phthalate)s and their use as modifiers for aromatic diamine‐cured epoxy resin

Poly(1,4‐cyclohexylenedimethylene phthalate) s, prepared by the reaction of phthalic anhydride and 1,4‐cyclohexane dimethanol (35/65 or 73/27 mol % cis/trans or trans alone), have been used to improve the toughness of bisphenol‐A diglycidyl ether epoxy resin cured with 4,4′‐diaminodiphenyl sulfone. The aromatic polyesters include poly(cis/trans‐1,4‐cyclohexylenedimethylene phthalate) (PCP) based on a commercial cyclohexanedimethanol, poly(trans‐1,4‐cyclohexylenedimethylene phthalate) (trans‐PCP) and poly(cis/trans‐1,4‐cyclohexylenedimethylene phthalate) (cis‐rich PCP) prepared from a cis‐rich diol. The polyesters used were soluble in the epoxy resin without solvents and were effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt% of PCP (MW 6400 g mol⁻¹) led to an 80% increase in the fracture toughness (K_IC) of the cured resin with no loss of mechanical and thermal properties. The toughening mechanism is discussed in terms of morphological and dynamic viscoelastic behaviours of the modified epoxy resin system. © 2000 Society of Chemical Industry