Preparation and cryogenic mechanical properties of epoxy resins modified by poly(ethersulfone)

A thermoplastic, poly(ethersulfone) (PES) was used to modify a bisphenol‐F based epoxy resin cured with an aromatic diamine. The initial mixtures before curing, prepared by melt mixing, were homogeneous. Scanning electron microscopy (SEM) micrographs of solvent‐etched fracture surfaces of the cured blends indicated that phase separation occurred after curing. The cryogenic mechanical behaviors of the epoxy resins were studied in terms of tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding behaviors at room temperature (RT). The addition of PES generally improved the tensile strength, elongation at break, and impact strength at both RT and 77 K except the RT tensile strength at 25 phr PES content. It was interesting to observe that and the maximum values of the tensile strength, elongation at break, and impact strength occurred at 20 phr PES content where a co‐continuous phase formed. Young's modulus decreased slightly with the increase of the PES content. Moreover, the tensile strength and Young's modulus at 77 K were higher than those at RT at the same composition, whereas the elongation at break and impact strength showed the opposite results. Finally, the differential scanning calorimetry analysis showed that the glass transition temperature (T_g) was enhanced by the addition of PES. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 612–624, 2008     

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     

Properties and morphologies of UV‐cured epoxy acrylate blend films containing hyperbranched polyurethane acrylate/hyperbranched polyester

The properties and morphologies of UV‐cured epoxy acrylate (EB600) blend films containing hyperbranched polyurethane acrylate (HUA)/hyperbranched polyester (HPE) were investigated. A small amount of HUA added to EB600 improved both the tensile strength and elongation at break without damaging its storage modulus (E′). The highest tensile strength of 31.9 MPa and an elongation at break around two times that of cured pure EB600 were obtained for the EB600‐based film blended with 10% HUA. Its log E′ (MPa) value was measured to be 9.48, that is, about 98% of that of the cured EB600 film. The impact strength and critical stress intensity factor (K_1c) of the blends were investigated. A 10 wt % HUA content led to a K_1c value 1.75 times that of the neat EB600 resin, and the impact strength of the EB600/HPE blends increased from 0.84 to 0.95 kJ m^?1 with only 5 wt % HPE addition. The toughening effects of HUA and HPE on EB600 were demonstrated by scanning electron microscopy photographs of the fracture surfaces of films. Moreover, for the toughening mechanism of HPE to EB600, it was suggested that the HPE particles, as a second phase in the cured EB600 film, were deformed in a cold drawing, which was caused by the difference between the elastic moduli of HPE and EB600. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3159–3170, 2005     

Synthesis and characterization of a novel polytriazole resin with low‐temperature curing character

A novel low‐temperature curing polytriazole resin was prepared from a triazide and a tetraalkyne and characterized. The resin can be cured at 70°C. The glass transition temperature T_g and thermal decomposition temperature T_d5 of the cured resin with the molar ratio of azide to alkyne group [A]/[B] = 1.0:1.0 reached 324 and 355°C, respectively. The study on the curing kinetics of the resin shows that the apparent activation energy of the curing reaction is 93 kJ mol^?1. The flexural strength of the cured resin reached 137.6 MPa at room temperature and 102.6 MPa at 185°C. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of carboxyl‐terminated (butadiene‐co‐acrylonitrile) loading on the mechanical and thermal properties of cured epoxy blends

A mixture of epoxy with liquid nitrile rubber, carboxyl‐terminated (butadiene‐co‐acrylonitrile) (CTBN) was cured under various temperatures. The cured resin was a two‐phase system, where spherical rubber domains were dispersed in the matrix of epoxy. The morphology development during cure was investigated by scanning electron microscope (SEM). There was slight reduction in the glass transition temperature of the epoxy matrix (T_g) on the addition of CTBN. It was observed that, for a particular CTBN content, T_g was found to be unaffected by the cure temperature. Bimodal distribution of particles was noted by SEM analysis. The increase in the size of rubber domains with CTBN content is due probably to the coalescence of the rubber particles. The mechanical properties of the cured resin were thoroughly investigated. Although there was a slight reduction in tensile strength and young's modulus, appreciable improvements in impact strength, fracture energy, and fracture toughness were observed. Addition of nitrile rubber above 20 parts per hundred parts of resin (phr) made the epoxy network more flexible. The volume fraction of dispersed rubbery phase and interfacial area were increased with the addition of more CTBN. A two‐phase morphology was further established by dynamic mechanical analysis (DMA). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2531–2544, 2004     

Novel photosensitive resin simultaneously with outstanding cryogenic strength and toughness for digital light processing three-dimensional Printing

With the increased demand for three-dimensional (3D) printing technology in various fields, it is important to develop high-performance resin that could withstand temperature changes to expand their application potential. A new photosensitive oligomer (BDM–DDM–ETPS–GMA) based on epoxy-terminated polyether siloxane (ETPS) and bismaleimide diphenylmethane/4, 4′-diaminodiphenylmethane (BDM–DDM) resin was synthesized and then mixed with other oligomers, reactive diluents, and photoinitiators to prepare a novel 3D printing resin. The results show that the resulting resins exhibit good fluidity and rapid photopolymerization ability, which satisfies the rheological prerequisites of 3D printing resin. Moreover, the incorporation of BDM–DDM–ETPS–GMA can simultaneously improve the cryogenic stiffness and toughness of commercial resin. Specifically, the tensile strength, elongation at break, flexural strength, impact strength, and storage modulus at ?30 °C of modified resin with 15% BDM–DDM–ETPS–GMA are 151.2 MPa, 10.9%, 146.2 MPa, 9.8 kJ/m², and 4,131 MPa, respectively, which are about 2.81, 1.70, 1.37, 1.81, and 1.54 times of that of commercial resin. A synergistic enhancement mechanism is believed to be attributed to these results, which includes the introduced flexible siloxane chain and the rigid bismaleimide structure as well as decreased cross-linking density. These attractive features of modified resins suggest that the method proposed herein is a new approach to develop high-performance 3D printing photosensitive resin simultaneously with outstanding cryogenic strength and toughness and thus has wide application potential in the aerospace, military industry, and other cutting-edge fields.     

Mechanical properties and curing kinetics of epoxy resins cured by various amino-terminated polyethers

<正>A high performance thermosetting epoxy resin crosslinkable at room temperature was obtained via directly moulding diglycidyl ether of bisphenol A(DGEBA) and flexibleα,ω-bisamino(n-alkylene)phenyl terminated poly(ethylene glycol).The influences of the n-alkylene inserted in aminophenyl of flexible amino-terminated polythers(ATPE) on the mechanical properties,fractographs and curing kinetics of the ATPE-DGEBA cured products were studied.The results show that the insertion of n-alkylene group into the aminophenyl group of the ATPE,on one hand,can significantly increase the strain relaxation rate and decrease glass transition temperature of the ATPE-DGEBA cured products,resulting in slight decrease of the Young's modulus and tensile strength,and significant increase of the toughness and elongation of the ATPE-DGEBA cured products.On the other hand,it can remarkably enhance the reactivity of amine with epoxy,much accelerating the curing rate of the ATPE-DGEBA systems.The activation energy of DGEBA cured by BAPTPE,BAMPTPE and BAEPTPE was 53.1,28.5 and 25.4 kJ·mol~(-1),respectively.The as-obtained ATPE-DGEBA cured products are homogeneous, transparent,and show excellent mechanical properties including tensile strength and toughness.Thus they are promising to have important applications in structure adhesives,casting bulk materials,functional coatings,cryogenic engineering, damping and sound absorbing materials.     

UV‐curable bismaleimides containing poly(dimethylsiloxane): Use as hydrophobic agent

The synthesis and characterization of poly(dimethylsiloxanes) bearing maleimides end‐groups (PDMSM) were carried out through imidization of maleic anhydride with three poly(dimethylsiloxanes) diamines of different molecular weights. Self‐photopolymerization of PDMSM was studied by Real‐Time Fourier Transform infrared spectroscopy (RT‐FTIR) and was possible even without photoinitiator (Darocur 1173). The reaction was found to proceed within seconds upon exposure to ultraviolet (UV) radiation to generate highly crosslinked polymer networks. The results indicated that these polymerizations were less sensitive to oxygen inhibition than the radical processes carried out on conventional UV‐curable acrylate resins. The thermal and mechanical properties of these resulting materials were studied starting from PDMS precursors with different molecular weights. These materials exhibit a low glass transition temperature (相似文献   

Investigation of the tensile properties of “epoxy resin‐monomer” systems using cationic UV‐crosslinkable blends

The compatibility of cycloaliphatic and aromatic multifunctional epoxides with several epoxide resins allows the development of a wide range of cationic radiation‐curable formulations. The influence of different “epoxide resin‐monomer” systems UV‐cured in the presence of suitable cationic photoinitiators on the resulting physicochemical film properties was studied, and the results are stated. Copyright © 2004 John Wiley & Sons, Ltd.     

Highly refractive polymer resin derived from sulfur‐containing aromatic acrylate

New sulfur‐containing polymers with high‐refractive indices and low birefringences have been developed as UV‐curable high‐refractive polymer resins. The polymers derived from 2,7‐bis[(2‐acryloylethyl)sulfanyl]thianthrene (2,7‐BAST) and 4,4′‐bis[(acryloyloxyethylthio)diphenylsulfide (4,4′‐BADS) were prepared by photopolymerization under UV irradiation. Transparent UV‐cured films were obtained in both cases. Both polymers showed good thermal stability, such as a 5% weight‐loss temperature at 355 °C under nitrogen and glass transition temperatures (T_g) in the range of 94–143 °C. They also showed high‐refractive indices of 1.6531 and 1.6645 at 632.8 nm and low birefringences of 0.0039 and 0.0069 in addition to high transparency in the visible region. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2604–2609, 2010     

Synthesis and characterization of novel phenolic resins containing aryl‐boron backbone and their utilization in polymeric composites with improved thermal and mechanical properties

In the present study, a novel aryl‐boron‐containing phenolic resin named as PBPR has been synthesized from phenol and formaldehyde in the presence of phenylboronic acid. The chemical structure of the PBPR was confirmed by Fourier transform infrared, nuclear magnetic resonance and X‐ray photoelectron spectroscopy. The molecular weight, viscosity and curing behavior were examined to demonstrate that PBPRs have better processability than common boric acid‐modified phenolic resin. The thermal stability and fracture toughness of the cured PBPRs were greatly enhanced, where the char yield at 1000°C (nitrogen atmosphere) and the glass transition temperature reached 70.0% and 218°C, respectively. The excellent mechanical and ablative properties of the PBPR composites may have benefited from the good interfacial adhesion between the resin matrix and the reinforced fiber. The flexural strength and the linear ablative rate are 436.8 ± 5.2 MPa and 0.010 mm/sec, respectively. This study opens a new window for the preparation of high‐performance ablative composites by designing a resin matrix containing an aryl‐boron backbone. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and properties of cross‐linkable high molecular weight fluorinated copolyimides

A series of novel high molecular weight fluorinated co‐polyimides (Co‐PIs) containing styryl side chain based on 1,3‐bis(2‐trifluoromethyl‐4‐aminophenoxy)‐5‐(2,3,4,5‐tetrafluorophenoxy)benzene (6FTFPB) were successfully synthesized. The weight‐average molecular weights (M_ws) and polydispersities of the co‐polyimides were in the range 8.93–10.81 × 10⁴ and 1.33–1.82, respectively. The co‐polyimide film showed excellent solubility in organic solvents, high tensile properties (tensile strength exceeded 91 MPa), excellent optical transparency (cutoff wavelength at 332–339 nm and light transparencies above 89% at a wavelength of 550 nm), and high thermal stability (5% thermal weight‐loss temperature up to 510 °C). The casting and spinning films could be cross‐linked by thermal curing. The cured films show better combination property (including excellent resistance to solvents) than that of co‐polyimides. For instance, the glass transition temperature of Co‐PI‐1 (the molar weight ratio of 6FTFPB was 30%) increased from 217 to 271 °C, the tensile strength enhanced from 94 to 96 MPa, the 5% thermal weight‐loss temperature improved from 514 to 525 °C. Moreover, after cured, Co‐PI‐1 film also has a coefficient of thermal expansion (CTE) value of 60.3 ppm °C^?1, low root mean square surface roughness (R_q) at 4.130 nm and low dielectric constant of 2.60. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 349–359     

Oligomeric bisphenol A‐based PEEK‐like phthalonitrile‐cure and polymer properties

The cure behavior and properties of oligomeric bisphenol A‐based PEEK‐like phthalonitrile (PN) are thoroughly examined in this article. The resin is easily processed from the melt at a relatively low temperature (150–200 °C) and the monomer cure occurs in a controlled manner as a function of the amine content and processing thermal conditions. Dynamic mechanical measurements and thermogravimetric analysis show that the polymer properties improve as the maximum PN postcure temperature is increased to 415 °C. The effects of the amine and polymer postcure conditions on the flexural and tensile properties of the PN polymer are investigated. The mechanical properties of the polymer are maximized after postcuring to moderate temperatures (330–350 °C). The polymer exhibits an average flexural strength and tensile strength at break of 117 and 71 MPa, respectively. After oxidative aging at 302 °C for 100 h, the polymer retains excellent mechanical properties. The average flexural and tensile strength retention of the polymers are 81 and 75%, respectively. Microscale calorimetric measurements reveal that the flammability parameters of the oligomeric PN are low compared to other thermosets. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3769–3777     

一种新型室温固化、耐高温环氧树脂体系及其性能

采用1-己基-3-甲基咪唑四氯化铁盐([C₆mim]FeCl₄)与混合胺复配室温(20 ℃)固化双酚A型环氧树脂E-51,并与其它脂肪胺类室温固化E-51体系在力学性能、热性能、耐老化性能方面的数据进行了比较,同时分析了[C₆mim]FeCl₄不同添加量对固化体系性能的影响,结果显示:[C₆mim]FeCl₄/混合胺复配室温固化E-51体系的室温拉伸强度可达90 MPa,高温(120 ℃)下也保持了良好的力学性能,热失重(5%)分解温度为310 ℃,200 ℃老化7 d后,拉伸强度为28 MPa,是一种可在高温下使用的新型环氧树脂室温固化体系。     

Investigation of processing,thermal, and mechanical properties of a new composite matrix‐benzoxazine containing aldehyde group

A new benzoxazine aldehyde group containing monomer 3‐phenyl‐6‐formyl‐3, 4‐dihydro‐2H‐1, 3‐benzoxazine (Ald‐B) was synthesized via the Mannich reaction of formaldehyde, p‐hydroxybenzaldehyde, and aniline. The viscosities and curing behavior of the resins were studied. The results indicated that Ald‐B has an initial viscosity lower than 0.110 Pa s at 90°C and the maximum temperature of the exotherm was at 196°C. Dynamic mechanical analysis (DMA) of the copolymer of Ald‐B and methylenedianiline‐type bis‐benzoxazine (B‐BOZ) showed only one T_g of 251°C and high crosslink density in the matrix. The thermal stability of the copolymer was improved noticeably and the char yield at 800°C is 68.4%. The tensile strength and flexural strength of this resin cast are 72 and 137 MPa, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Procedures conditioning the absorption/desorption behavior of cold‐cured epoxy resins

The absorption/desorption behavior of a commercial cold‐cured bisphenolic epoxy resin, subjected to different treatments prior to exposure to water, was analyzed. The epoxy system has been already used as both matrix and adhesive for the manufacture and application, respectively, of fiber reinforced polymers composites employed for rehabilitation procedures. The effects of different curing, conditioning, and storing conditions on the water absorption/desorption process taking place in the cured resin were evaluated. The different conditioning procedures used to dry the specimens before their exposure to water caused a different extent of physical aging and of curing on each system, influencing the amount and the rate of diffusion of the water molecules inside the specimens. Moreover, if the specimens are subjected to thermohygrometric cycles prior to immersion in water, the rate of diffusion and the amount of water also depends on the presence of water molecules inside the cured resins not easy to remove by any drying treatment. During all the hygrometric treatments performed, a deaging process took place. The kinetic of this deaging process for the not‐fully cured systems depends on the additional crosslinking taking place in the samples. The different procedures used to condition the specimens also affect the variations in glass transition temperature (T_g) of the cured systems during and after immersion in water. Finally, the different drying procedures employed proved to be not equally appropriate for cold‐cured epoxy resins. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1320–1336, 2008     

Influence of varying hard segments on the properties of chemically crosslinked moisture‐cured polyurethane‐urea

Polyurethane prepolymers are widely used in the reactive hot melt adhesives and moisture‐cured coatings. The chemically crosslinked moisture‐cured formulation based on PEG‐1000 and isophorone diisocyanate was prepared with NCO/OH ratio of 1.6:1.0. Trimethylol propane was used as a crosslinking agent. The excess isocyanate of the prepolymer was chain extended in the ratio of 2:1 (NCO/OH) with different aliphatic diols, and 4:1 with different aromatic diamines. The polymer network maturation during moisture cure was followed by dynamic mechanical thermal analyzer (DMTA) instrument. The thermal and dynamic mechanical properties of the crosslinked polymers were evaluated using thermogravimetric analysis, differential scanning calorimetric analysis and DMTA. Surface properties were evaluated through angle‐resolved X‐ray photoelectron spectroscopy. The present article discusses the physical properties of moisture‐cured polyurethane‐urea (MCPU) containing chemical crosslinks in the hard segment. The complete moisture‐cured polymers showed amorous results toward room temperature modulus, tensile strength, hardness, thermal stability, and transparency. The surface properties showed the enrichment of soft segments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 102–118, 2006     

Adhesives and coatings based on phenolic/epoxy resins

Low molecular weight epoxy resin based on bis (4‐hydroxy phenyl) 1,1 cyclohexane was prepared and modified with various types of the prepared phenolic resins. Phenol–, cresol–, resorcinol–and salicylic acid–formaldehyde resins were used. The optimum conditions of formulation and curing process were studied to obtain modified wood adhesives characterized by high tensile shear strength values. This study indicated that the more suitable conditions are 1:2 weight ratio of phenol–or cresol–formaldehyde to epoxy resin in the presence of phthalic anhydride (20 wt%) of the resin content as a curing agent at 150°C for 80 min. Resorcinol–or salicylic acid–formaldehyde/epoxy resins formulated at 1:2 weight ratio were cured in the presence of paraformaldehyde (20 wt%) at 150°C for 60 min. The effect of the structure of phenolic resins on the tensile shear strength values of formulated resin samples, when mixed with the epoxy resins and cured under the previously mentioned optimum conditions for different times, was investigated. Metallic and glass coatings from the previous resins were also prepared and evaluated as varnishes or paints. Copyright © 1999 John Wiley & Sons, Ltd.     

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.     

Dielectric properties of self‐catalytic interpenetrating polymer network based on modified bismaleimide and cyanate ester resins

Bismaleimide (BMI) resins with good thermal stability, fire resistance, low water absorption, and good retention of mechanical properties at elevated temperatures, especially in hot/wet environments, have attracted more attention in the electronic and aerospace industries. However, their relatively high dielectric constant limits their application in the aforementioned fields. In this work, a new promising approach is presented that consists of the formation of a self‐catalytic thermoset/thermoset interpenetrating polymer network. Interpenetrating polymer networks (IPNs) based on modified BMI resin (BMI/DBA) and cyanate ester (b10) were synthesized via prepolymerization followed by thermal curing. The self‐catalytic curing mechanism of BMI/DBA‐CE IPN resin systems was examined by differential scanning calorimetry. The dielectric properties of the cured BMI/DBA‐CE IPN resin systems were evaluated by a dielectric analyzer and shown in dielectric properties‐temperature‐log frequency three‐dimensional plots. The effect of temperature and frequency on the dielectric constant of the cured BMI/DBA‐CE IPN resin systems is discussed. The composition effect on the dielectric constant of the cured IPN resin systems was analyzed on the basis of Maxwell's equation and rule of mixture. The obtained BMI/DBA‐CE IPN resin systems have the combined advantages of low dielectric constant and loss, high‐temperature resistance, and good processability, which have many applications in the microelectronic and aerospace industries. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1123–1134, 2003