A comparative study on the preparation and characterization of aromatic and aliphatic bismaleimides‐modified polyurethane–epoxy interpenetrating polymer network matrices

Interpenetrating polymer networks of bismaleimide‐modified polyurethane–epoxy systems were prepared using the aliphatic and aromatic bismaleimides‐ and polyurethane‐modified epoxy and cured in the presence of 4,4′‐diaminodiphenylmethane. Infrared spectral analysis was used to confirm the polyurethane‐crosslinked epoxy (PU–EP). The matrices developed were characterized by mechanical, thermal, electrical, and morphological studies. The results obtained from the mechanical studies indicate that the incorporation of polyurethane and bismaleimides into epoxy increased the tensile strength, flexural strength, and impact strength, according to their nature and percentage concentration. The results obtained from the thermal and electrical studies indicate that the incorporation of polyurethane into epoxy decreased the thermal properties (glass transition temperature, heat distortion temperature (HDT), thermal stability) and electrical properties (dielectric strength, volume and surface resistivity, and arc resistance). The incorporation of aromatic bismaleimide into the polyurethane‐modified epoxy system increased the glass transition temperature, thermal stability, and electrical properties. Decreased values of glass transition and HDT were obtained in the case of aliphatic bismaleimide‐modified polyurethane–epoxy system. Surface morphology of modified epoxy systems was studied using scanning electron microscopy, and it was found that the polyurethane‐modified epoxy systems exhibited heterogeneous morphology and bismaleimides‐modified epoxy systems showed a homogeneous morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3592–3602, 2006     

Preparation and characterization of 3,3′‐bis (maleimidophenyl)phenylphosphine oxide (BMI)/polysulfone modified epoxy intercrosslinked matrices

An intercrosslinked network of polysulfone (PSF)—bismaleimide (BMI) modified epoxy matrix system was made by using diglycidyl ether of bisphenol A (DGEBA) epoxy resin, hydroxyl terminated polysulfone and bismaleimide (3,3′‐bis(maleimidophenyl) phenylphosphine oxide) with diaminodiphenylmethane (DDM) as curing agent. BMI–PSF–epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and heat deflection temperature (HDT) analysis. The matrices, in the form of castings, were characterized for their mechanical properties such as tensile strength, flexural strength, and unnotched Izod impact test as per ASTM methods. Mechanical studies indicated that the introduction of polysulfone into epoxy resin improves the toughness to an appreciable extent with insignificant increase in stress–strain properties. DSC studies indicated that the introduction of polysulfone decreases the glass transition temperature, whereas the incorporation of bismaleimide into epoxy resin influences the mechanical and thermal properties according to its percentage content. DSC thermograms of polysulfone as well as BMI modified epoxy resin show a unimodal reaction exotherm. The thermal stability and flame retardant properties of cured epoxy resins were improved with the introduction of bismaleimide and polysulfone. Water absorption characteristics were studied as per ASTM method and the morphology of the BMI modified epoxy and PSF‐epoxy systems were studied by scanning electron microscope. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Preparation and characterization of bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane)–unsaturated polyester modified epoxy intercrosslinked matrices

An intercrosslinked network of unsaturated polyester–bismaleimide modified epoxy matrix systems was developed. Epoxy systems modified with 10, 20, and 30% (by weight) of unsaturated polyester were made by using epoxy resin and unsaturated polyester with benzoyl peroxide and diaminodiphenylmethane as curing agents. The reaction between unsaturated polyester and epoxy resin was confirmed by IR spectral studies. The unsaturated polyester toughened epoxy systems were further modified with 5, 10, and 15% (by weightt) of bismaleimide (BMI). The matrices, in the form of castings, were characterized for their mechanical properties. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the matrix samples were performed to determine the glass transition temperature (T_g) and thermal degradation temperature of the systems, respectively. Mechanical properties, viz: tensile strength, flexural strength, and plain strain fracture toughness of intercrosslinked epoxy systems, were studied by ASTM methods. Data obtained from mechanical and thermal studies indicated that the introduction of unsaturated polyester into epoxy resin improves toughness but with a reduction in glass transition, whereas the incorporation of bismaleimide into epoxy resin improved both mechanical strength and thermal behavior of epoxy resin. The introduction of bismaleimide into unsaturated polyester‐modified epoxy resin altered thermomechanical properties according to their percentage concentration. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2853–2861, 2002     

Preparation and characterization of siliconized epoxy‐1,2‐bis(maleimido)ethane intercrosslinked matrix materials

Novel intercrosslinked networks of siliconized epoxy‐1,2‐bis(maleimido)ethane matrix systems are developed. The siliconization of epoxy resin is carried out by using 5–15% hydroxyl‐terminated poly(dimethylsiloxane) with γ‐aminopropyltriethoxysilane as a crosslinking agent and dibutyltin dilaurate as a catalyst. The siliconized epoxy systems are further modified with 5–15% 1,2‐bis(maleimido)ethane and cured by using diaminodiphenylmethane. The prepared neat resin castings are characterized for their mechanical properties. Mechanical studies indicate that the introduction of siloxane into these epoxy resins improves the toughness with a reduction in the stress–strain values, whereas incorporation of bismaleimide (BMI) into the epoxy resin improves the stress–strain properties with a lowering of the toughness. The introduction of both siloxane and BMI into the epoxy resin influences the mechanical properties according to their content percentages. Differential scanning calorimetry (DSC), thermogravimetry, and heat distortion temperature analyses are also carried out to assess the thermal behavior of the matrix materials that are developed. DSC thermograms of the BMI modified epoxy systems show unimodal reaction exotherms. The glass‐transition temperature, thermal degradation temperature, and heat distortion temperature of the cured BMI modified epoxy and siliconized epoxy systems increase with increasing BMI content. The water absorption behavior of the matrix materials is also studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3808–3817, 2003     

Studies on mechanical,thermal, and morphology of diglycidylether‐terminated polydimethylsiloxane‐modified epoxy–bismaleimide matrices

An epoxy matrix system modified by diglycidylether‐terminated polydimethylsiloxane (DGETPDMS) and bismaleimide (BMI) was developed. Epoxy systems modified with 4, 8, and 12% (by wt) of DGETPDMS were made using epoxy resin and DGETPDMS, with diaminodiphenylmethane as the curing agent. The DGETPDMS‐toughened epoxy systems were further modified with 4, 8, and 12% (by wt) of BMI, namely (N,N′‐bismaleimido‐4,4′‐diphenylmethane). DGETPDMS/BMI/epoxy matrices were characterized using differential scanning calorimetry, thermogravimetric analysis, and heat deflection temperature analysis. The matrices, in the form of castings, were characterized for their mechanical properties, viz. tensile strength, flexural strength, and impact test, as per ASTM methods. Mechanical studies indicate that the introduction of DGETPDMS into epoxy resin improves the impact strength, with reduction in tensile strength, flexural strength, and glass transition temperature, whereas the incorporation of BMI into epoxy resin enhances the mechanical and thermal properties according to its percentage content. However, the introduction of both DGETPDMS and BMI enhances the values of thermomechanical properties according to their percentage content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 668–674, 2006     

Preparation and characterization of siliconized epoxy/bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane) intercrosslinked matrices for engineering applications

Novel hybrid intercrosslinked networks of hydroxyl‐terminated polydimethylsiloxane‐modified epoxy and bismaleimide matrix systems have been developed. Epoxy systems modified with 5, 10, and 15 wt % of hydroxyl‐terminated polydimethylsiloxane (HTPDMS) were developed by using epoxy resin and hydroxyl‐terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane (γ‐APS) as compatibilizer and dibutyltindilaurate as catalyst. The reaction between hydroxyl‐terminated polydimethylsiloxane and epoxy resin was confirmed by IR spectral studies. The siliconized epoxy systems were further modified with 5, 10, and 15 wt % of bismaleimide (BMI). The matrices, in the form of castings, were characterized for their mechanical properties. Differential scanning calorimetry and thermogravimetric analysis of the matrix samples were also performed to determine the glass‐transition temperature and thermal‐degradation temperature of the systems. Data obtained from mechanical studies and thermal characterization indicate that the introduction of siloxane into epoxy improves the toughness and thermal stability of epoxy resin with reduction in strength and modulus values. Similarly the incorporation of bismaleimde into epoxy resin improved both tensile strength and thermal behavior of epoxy resin. However, the introduction of siloxane and bismaleimide into epoxy enhances both the mechanical and thermal properties according to their percentage content. Among the siliconized epoxy/bismaleimide intercrosslinked matrices, the epoxy matrix having 5% siloxane and 15% bismaleimide exhibited better mechanical and thermal properties than did matrices having other combinations. The resulting siliconized (5%) epoxy bismaleimide (15%) matrix can be used in the place of unmodified epoxy for the fabrication of aerospace and engineering composite components for better performance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 38–46, 2001     

Studies on thermal and morphological behavior of siliconized epoxy bismaleimide matrices

Novel bismaleimide‐modified siliconized epoxy intercrosslinked network systems were developed. Siliconized epoxy systems containing 5, 10, and 15% siloxane units were prepared using epoxy resin and hydroxyl‐terminated polydimethylsiloxane (HTPDMS) with γ‐aminopropyltriethoxysilane (γ‐APS) as a compatibilizer and dibutyltindilaurate as a catalyst. The siliconized epoxy systems were further modified with 5, 10, and 15% (wt %) of bismaleimide [(N,N′‐bismaleimido‐4,4′‐diphenylmethane) (BMI)] and cured by diaminodiphenylmethane (DDM). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and heat‐distortion temperature measurement of the matrix samples were carried out to assess their thermal behavior. DSC thermograms of the BMI‐modified epoxy systems show unimodel reaction exotherms. The glass transition temperature (T_g) of the cured BMI‐modified epoxy and siliconized epoxy systems increases with increasing BMI content. Thermogravimetric analysis and heat‐distortion temperature measurements indicate that the thermal degradation temperature and heat‐distortion temperature of the BMI‐modified epoxy and siliconized epoxy systems increase with increasing BMI content. The morphology of the BMI‐modified siliconized epoxy systems was also studied by scanning electron microscopy (SEM). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2330–2346, 2001     

Phosphonate‐containing bismaleimide resins. II. Preparation and characteristics of reactive blends of phosphonate‐containing bismaleimide and epoxy

Two kinds of phosphonate‐containing bismaleimide (BMI) monomers, phenyl‐(4,4′‐bismaleimidophenyl) phosphonate and ethyl‐(4,4′‐bismaleimido‐phenyl) phosphonate, were synthesized and added through blending to two epoxy systems for the study of their applications as reactive flame retardants. The thermal behaviors of the BMI monomers in both kinds of epoxy systems, bisphenol and phenol–novolac, were similar. An increase in the BMI contents increased the storage modulus and glass‐transition temperature but slightly reduced the mechanical strength of the epoxy blends. The pyrolysis models of both BMI blends in the two epoxy systems were quite alike. Although the initial pyrolysis temperatures of all the blending systems gradually decreased as the phosphorous content increased, the flame retardancy of all the phosphonate‐containing epoxy systems was promoted significantly by increasing contents of BMI. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2375–2386, 2004     

Diallyl bisphenol A—novolac epoxy system cocured with bisphenol‐A‐bismaleimide—cure and thermal properties

Novolac epoxy (EPN)—2,2′‐diallyl bisphenol A (DABA) resin system was modified by cocuring it with bisphenol A bismaleimide (BMI). Molar concentration of BMI in the stochiometric blend of EPN and DABA was varied from 0.5 to 2.0. The cure optimization was done using DSC, IR spectroscopy, and rheological studies. The curing proceeded by phenol‐epoxy and Alder‐ene reactions. The performance of the ternary Epoxy‐Allyl phenolic‐Bismaleimide system was evaluated through their thermal and dynamic mechanical characterization. BMI improved the overall thermal stability and the modulus of the resultant composites. The increase in BMI concentration in the system resulted in enhanced glass transition temperature with a consequent improvement in high temperature performance typically estimated by their lap shear strength at high temperatures. The high temperature performance of the epoxy‐phenol‐bismaleimide (EPB) system was found to be far superior to the epoxy‐phenol (EP)system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

玉米秸秆木质素改性环氧树脂的制备与性能

将玉米秸秆木质素与双酚A环氧树脂混合,于100℃下预处理1 h,以改善环氧树脂的性能。对预处理后环氧树脂的黏度进行了测试,对改性环氧树脂与聚酰胺固化后材料的力学性能、动态力学性能、热稳定性以及燃烧性能进行了综合测试,考察了不同质量分数的玉米秸秆木质素对改性环氧树脂性能的影响。结果表明:以固化体系的总质量为基准,在w(木质素)=0~7%的范围内,与未添加木质素的环氧树脂相比,随着木质素质量分数的增加,改性环氧树脂22℃下的黏度从1 220 m Pa·s增大到13 220 m Pa·s;改性环氧树脂固化物的弯曲强度随木质素质量分数的增加先升高后降低,在w(木质素)=3%时达到最大值83.2 MPa,但其冲击强度下降,由20.7 MPa降低为13.6 MPa;改性环氧树脂固化物的玻璃化转变温度(Tg)随木质素质量分数的增加而增加,w(木质素)=5%时Tg提高了4.8℃;改性环氧树脂固化物的热稳定性有所改善,w(木质素)=7%时热失重50%的温度提高13℃,同时木质素的加入能够改善环氧树脂的阻燃性能。     

Polyurethane‐modified epoxy resin: Solventless preparation and properties

A polyurethane‐modified epoxy resin system with potential as an underfill material in electronic packaging and its preparation procedure were studied. The procedure enabled the practical incorporation of an aliphatic polyurethane precursor, synthesized from poly(ethylene glycol) and hexamethylene diisocyanate without a solvent, as a precrosslinking agent into a conventional epoxy resin. With a stoichiometric quantity of the polyurethane precursor added to the epoxy (ca. 5 phr), the polyurethane‐modified epoxy resin, mixed with methylene dianiline, exhibited a 36% reduction in the contact angle with the epoxy–amine surface, a 31% reduction in the cure onset temperature versus the control epoxy system, and a viscosity within the processable range. The resultant amine‐cured thermosets, meanwhile, exhibited enhanced thermal stability, flexural strength, storage modulus, and adhesion strength at the expense of a 5% increase in the coefficient of thermal expansion. Exceeding the stoichiometric quantity of the polyurethane precursor, however, reduced the thermal stability and modulus but further increased the coefficient of thermal expansion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and thermomechanical characterization of polyurethane elastomers extended with α,ω‐alkane diols

A series of polyurethane (PU) elastomers was prepared by the reaction of poly(?‐caprolactone) and 4,4′‐diphenylmethane diisocyanate, which was extended with a series of chain extenders (CEs) having 2–10 methylene units in their structure. The completion of the reaction was confirmed by Fourier transform infrared spectroscopy. The chemical structures of the synthesized PU samples were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR spectroscopy, and the thermal properties were determined by thermogravimetric analysis, DSC, and dynamic mechanical thermal analysis techniques. The mechanical properties were also studied and are discussed. The thermogravimetric analysis and DSC analysis showed that CE length had a considerable effect on the thermal properties of the prepared samples. The dynamic mechanical thermal analysis and damping peaks were also affected by the number of methylene units in the CE length. The elastomer extended with 1,2‐ethane diol exhibited optimum thermal properties, whereas the elastomer based on 1,10‐decane diol displayed the worst thermal properties. Tensile strength and elongation at break decreased with increasing CE length, whereas hardness showed the opposite trend. The glass‐transition temperature moved toward lower temperatures with increasing CE length. The decrease in the glass‐transition temperature and tensile properties were interpreted in terms of decreasing hard segments and increasing chain flexibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of siliconized epoxy-1,3-bis(maleimido)benzene intercrosslinked matrix materials

Intercrosslinked network of siliconized epoxy-1,3-bis(maleimido)benzene matrix systems have been developed. The siliconization of epoxy resin was carried out by using various percentages of (5-15%) hydroxyl-terminated polydimethylsiloxane (HTPDMS) with γ-aminopropyltriethoxysilane (γ-APS) as crosslinking agent and dibutyltindilaurate as catalyst. The siliconized epoxy systems were further modified with various percentages of (5-15%) 1,3-bis(maleimido)benzene (BMI) and cured by using diaminodiphenylmethane (DDM). The neat resin castings prepared were characterized for their mechanical properties. Mechanical studies indicate that the introduction of siloxane into epoxy resin improves the toughness of epoxy resin with reduction in the values of stress-strain properties whereas, incorporation of bismaleimide into epoxy resin improves stress-strain properties with lowering of toughness. However, the introduction of both siloxane and bismaleimide into epoxy resin influences the mechanical properties according to their percentage content. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and measurement of heat distortion temperature were also carried out to assess the thermal behavior of the matrix samples. DSC thermogram of the BMI modified epoxy systems show unimodel reaction exotherms. The glass transition temperature (T_g), thermal degradation temperature and heat distortion temperature of the cured BMI modified epoxy and siliconized epoxy systems increase with increasing BMI content and this may be due to the homopolymerization of BMI rather than Michael addition reaction. The morphology of the BMI modified epoxy and siliconized epoxy systems were also studied by scanning electron microscopy.     

Synthesis,thermal properties,and flame retardance of the epoxy‐silsesquioxane hybrid resins

Epoxy/silsesquioxane‐OH (EP‐SDOH, ED) hybrid resins were prepared from cyclohexyl‐disilanol silsesquioxane (SDOH) and diglycidyl ether of bisphenol A via the reaction between silanol and the oxirane group, with the cobalt naphthanate as a catalyst. It was found that incorporation of SDOH allows the reaction between oxirane ring and Si? OH, and the silsesquioxane cage structure can be the main chain or as the side chain of the hybrid resin. The EP‐SDOH hybrid resins with various SDOH contents were cured by 4,4′‐diaminodiphenylsulphone, and the curing reaction was investigated by differential scanning calorimetry. The curing characteristics of EP‐SDOH hybrids had been observed to be influenced by the content of SDOH in the hybrid. The differential scanning calorimetry thermograms indicated that the EP‐SDOH hybrid exhibited a higher initial temperature, peak temperature, as well as final temperature than those of the pure epoxy resin when cured by the same curing agent 4,4′‐diaminodiphenylsulphone. The curing kinetic parameters were calculated by using the Ozawa method and the results indicated that EP‐SDOH hybrids possess the same curing mechanism as the pure epoxy resin. The properties of the cured EP‐SDOH hybrid resins such as the glass transition temperature (T_g), dynamic mechanical analysis, thermal stability, as well as the flame retardance were also investigated, and the results showed that introducing silsesquioxane‐OH unit into epoxy resin successfully modified the local structure, made the chain stiffness, restrict the chain mobility, and eventually improved thermal stability and flame retardance of epoxy resin. POLYM. ENG. SCI., 47:225–234, 2007. © 2007 Society of Plastics Engineers.     

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     

Nanoclay filled soy‐based polyurethane foam

Polyurethane foam was fabricated from polymeric diphenylmethane diisocyanate (pMDI) and soy‐based polyol. Nanoclay Cloisite 30B was incorporated into the foam systems to improve their thermal stabilities and mechanical properties. Neat polyurethane was used as a control. Soy‐based polyurethane foams with 0.5–3 parts per hundred of polyols by weight (php) of nanoclay were prepared. The distribution of nanoclay in the composites was analyzed by X‐ray diffraction (XRD), and the morphology of the composites was analyzed through scanning electron microscopy (SEM). The thermal properties were evaluated through dynamic mechanical thermal analysis (DMTA). Compression and three‐point bending tests were conducted on the composites. The densities of nanoclay soy‐based polyurethane foams were higher than that of the neat soy‐based polyurethane foam. At a loading of 0.5 php nanoclay, the compressive, flexural strength, and modulus of the soy‐based polyurethane foam were increased by 98%, 26%, 22%, and 65%, respectively, as compared to those of the neat soy‐based polyurethane foam. The storage modulus of the soy‐based polyurethane foam was improved by the incorporation of nanoclay. The glass transition temperature of the foam was increased as the nanoclay loading was increased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of epoxy content on dynamic mechanical behaviour of PEI‐toughened dicyanate–novolac epoxy blends

By varying the cyanate/epoxy ratio, three polyetherimide(PEI)‐modified bisphenol A dicyanate–novolac epoxy resin blends with different epoxy contents were prepared. The effects of epoxy content on the dynamic mechanical behaviour of those blends were investigated by dynamic mechanical thermal analysis. The results showed that the glass transition temperature of the cyanate–epoxy network (T_g1) in the modified blend decreases with epoxy content. When the epoxy content increases, both the width of the glass transition of the cyanate–epoxy network and its peak density are depressed substantially. Although the tangent delta peak value of PEI is basically independent of epoxy content, the T_g of PEI (T_g2) decreases with epoxy content. T_g1 is independent of the PEI loading. When T_g1 is lower than T_g2, however, the T_g1 in the blend with revised phase structure is substantially lower than other blends. Copyright © 2004 Society of Chemical Industry     

Thermal characterization of carbon‐nanofiber‐reinforced tetraglycidyl‐4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone epoxy composites

The thermal properties of carbon nanofibers (CNF)/epoxy composites, composed of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) resin and 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent, were investigated with differential scanning calorimetry (DSC), thermogravimetric analysis, and dynamic mechanical thermal analysis. DSC results showed that the presence of CNF had no pronounced influence on the heat of the cure reaction. However, the incorporation of CNF slightly improved the thermal stability of the epoxy. Furthermore, the storage modulus of the TGDDM/DDS epoxy was significantly enhanced, whereas the glass‐transition temperature was not significantly affected, upon the incorporation of CNFs. The storage modulus of 5 wt % CNF/epoxy composites at 25°C was increased by 35% in comparison with that of the pure epoxy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 295–298, 2006     

Mechanical and morphological properties of organic–inorganic,hybrid, clay‐filled,and cyanate ester/siloxane toughened epoxy nanocomposites

Organic–inorganic hybrids involving cyanate ester and hydroxyl‐terminated polydimethylsiloxane (HTPDMS) modified diglycidyl ether of bisphenol A (DGEBA; epoxy resin) filled with organomodified clay [montmorillonite (MMT)] nanocomposites were prepared via in situ polymerization and compared with unfilled‐clay macrocomposites. The epoxy‐organomodified MMT clay nanocomposites were prepared by the homogeneous dispersion of various percentages (1–5%), and the resulting homogeneous epoxy/clay hybrids were modified with 10% HTPDMS and γ‐aminopropyltriethoxysilane as a coupling agent in the presence of a tin catalyst. The siliconized epoxy/clay prepolymer was further modified separately with 10% of three different types of cyanate esters, namely, 4,4′‐dicyanato‐2,2′‐diphenylpropane, 1,1′‐bis(3‐methyl‐4‐cyanatophenyl) cyclohexane, and 1,3‐dicyanato benzene, and cured with diaminodiphenylmethane as a curing agent. The reactions during the curing process between the epoxy, siloxane, and cyanate were confirmed by Fourier transform infrared analysis. The results of dynamic mechanical analysis showed that the glass‐transition temperatures of the clay‐filled hybrid epoxy systems were lower than that of neat epoxy. The data obtained from mechanical studies implied that there was a significant improvement in the strength and modulus by the nanoscale reinforcement of organomodified MMT clay with the matrix resin. The morphologies of the siloxane‐containing, hybrid epoxy/clay systems showed heterogeneous character due to the partial incompatibility of HTPDMS. The exfoliation of the organoclay was ascertained from X‐ray diffraction patterns. The increase in the percentage of organomodified MMT clay up to 5 wt % led to a significant improvement in the mechanical properties and an insignificant decrease in the glass‐transition temperature versus the unfilled‐clay systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and characterization of bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane)–vinyl ester oligomer–modified unsaturated polyester interpenetrating matrices for advanced composites

Interpenetrating networks of varying percentages of bismaleimide (BMI) in vinyl ester oligomer (VEO) modified unsaturated polyester (UP) matrices have been developed. Vinyl ester oligomer was prepared by reacting commercially available epoxy resin GY 250 (Ciba‐Geigy) and acrylic acid, and used as a toughening agent for unsaturated polyester resin. Unsaturated polyesters modified with 10, 20, and 30 wt % vinyl ester oligomer were made. The VEO toughened unsaturated polyester matrix systems, further modified with 5, 10, and 15 wt % bismaleimide (BMI). BMI–VEO–UP matrices were characterized using differential scanning calorimetry, thermogravimetric analysis, and heat deflection temperature analysis. The matrices, in the form of castings, were characterized for their mechanical properties according to ASTM methods: tensile strength, flexural strength, and unnotched Izod impact test. Data obtained from mechanical studies and thermal characterization indicate that the introduction of VEO and BMI into unsaturated polyester resin improves thermomechanical properties according to their percentage concentration. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2502–2508, 2002