Toughening epoxy resins with solid acrylonitrile–butadiene rubber

The feasibility of using solid acrylonitrile–butadiene rubbers (NBR) with 19 and 33% w/w acrylonitrile to toughen diglycidyl ether of bisphenol A (DGEBA) epoxy resins has been investigated. Thermal analysis experiments revealed a two‐phase morphology of these rubber‐modified epoxies. However, the higher content of acrylonitrile in the rubber caused better compatibility between NBR and the epoxy resin. The rubber with 33% acrylonitrile was found to be an effective toughening agent for DGEBA epoxy resins. Fracture surface studies and also the high tensile strength of crosslinked high molecular weight NBR suggest that the toughening effect should arise from rubber bridging and tearing mechanisms. © 2000 Society of Chemical Industry     

Modification of epoxy resin with α,ω-oligo(butylmethacrylate)diols

Novel liquid rubbers based on bishydroxy-terminated oligo(butylmethacrylate) were used to toughen anhydride-cured epoxy resins. Concentration and molecular weight of the toughening agents were varied in order to examine the effects on important mechanical properties, such as toughness, strength, stiffness, and glass transition temperature. Experimental data show that telechelic methacrylates are suitable toughening agents for epoxies. The compatibility between resin and toughener can be adjusted by varying the molecular weight of the rubber. The best results are obtained by modifying an epoxy resin with 10 wt% of bishydroxy-terminated oligo(butylmethacrylate) of a molecular weight of 5000 g/mol. Fracture toughness K_lc increases by 150% accompanied by a decrease in modulus of only 11% and in strength of 16%, as compared to the corresponding properties of the neat resin. Due to an almost complete phase separation of the rubber upon curing, the glass transition temperature is scarcely affected. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 785–796, 1998     

Synthesis and characterization of diphenylsilanediol modified epoxy resin and curing agent

A series of diphenylsilanediol modified epoxy resins and novel curing agents were synthesized. The modified epoxy resins were cured with regular curing agent diethylenetriamine (DETA); the curing agents were applied to cure unmodified diglycidyl ether of bisphenol A epoxy resin (DGEBA). The heat resistance, mechanical property, and toughness of all the curing products were investigated. The results showed that the application of modified resin and newly synthesized curing agents leads to curing products with lower thermal decomposition rate and only slightly decreased glass transition temperature (T_g), as well as improved tensile modulus and tensile strength. In particular, products cured with newly synthesized curing agents showed higher corresponding temperature to the maximum thermal decomposition rate, comparing with products of DGEBA cured by DETA. Scanning electron microscopy micro images proved that a ductile fracture happened on the cross sections of curing products obtained from modified epoxy resins and newly synthesized curing agents, indicating an effective toughening effect of silicon–oxygen bond.     

New thermosetting resin from poly(p‐vinylphenol) based benzoxazine and epoxy resin

Poly(p‐vinylphenol) (VP) based benzoxazine was prepared from VP, formaline, and aniline. The curing behavior of the benzoxazine with the epoxy resin and the properties of the cured resin were investigated. Consequently, the curing reaction did not proceed at low temperatures, but it proceeded rapidly at higher temperatures without a curing accelerator. The reaction induction time or cure time of the molten mixture from VP based benzoxazine and epoxy resin was found to decrease, compared with those from conventional bisphenol A based benzoxazine and epoxy resin. The curing reaction rate of VP based benzoxazine and epoxy resin increased more than that of conventional bisphenol A based benzoxazine and epoxy resin. The properties of the cured resin from neat resins and from reinforced resins with fused silica were evaluated. The cured resins from VP based benzoxazine and epoxy resin showed good heat resistance, mechanical properties, electrical insulation, and water resistance compared to the cured resin from VP and epoxy resin using imidazole as the catalyst. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 555–565, 2001     

Epoxidized soybean oil modified using fatty acids as tougheners for thermosetting epoxy resins: Part 2—Effect of curing agent and epoxy molecular weight

A series of bio-rubber (BR) tougheners for thermosetting epoxy resins was prepared by grafting renewable fatty acids with different chain lengths onto epoxidized soybean oil at varying molar ratios. BR-toughened samples were prepared by blending BRs with diglycidyl ether of bisphenol A resins, Epon 828 and Epon 1001F, at different weight fractions and stoichiometrically cured using an amine curing agent, 4, 4′-methylene biscyclohexanamine (PACM). Fracture toughness properties of the unmodified and BR toughened polymer samples—including critical strain energy release rate (G_Ic), and critical stress intensity factor (K_Ic)—were measured to investigate the toughening effect of prepared BRs. It was found that the degree of phase separation and toughening were more controllable relative to similar polymers cured using the aromatic curing agent Epikure W, and the use of higher molecular epoxy resins produces a synergistic effect increasing the toughness much more than similar polymers made with lower molecular weight epoxy resins. Average BR domain sizes ranging from 200 to 900 nm were observed, and formulations with G_Ic, values K_Ic as high as 1.0 kJ/m² and 1.4 MPa m^1/2 were attained respectively for epoxy systems with T_g greater than 130°C.     

Synthesis of a novel phosphorus‐containing dicyclopentadiene novolac hardener and its cured epoxy resin with improved thermal stability and flame retardancy

A novel phosphorus‐containing dicyclopentadiene novolac (DCPD‐DOPO) curing agent for epoxy resins, was prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and n‐butylated dicyclopentadiene phenolic resin (DCPD‐E). The chemical structure of the obtained DCPD‐DOPO was characterized with FTIR, ¹H NMR and ³¹P NMR, and its molecular weight was determined by gel permeation chromatography. The flame retardancy and thermal properties of diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with DCPD‐DOPO or the mixture of DCPD‐DOPO and bisphenol A‐formaldehyde Novolac resin 720 (NPEH720) were studied by limiting oxygen index (LOI), UL 94 vertical test and cone calorimeter (CCT), and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. It is found that the DCPD‐DOPO cured epoxy resin possess a LOI value of 31.6% and achieves the UL 94 V‐0 rating, while its glass transition temperature (T_g) is a bit lower (133 °C). The T_g of epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 increases to 137 °C or above, and the UL 94 V‐0 rating can still be maintained although the LOI decreases slightly. The CCT test results demonstrated that the peak heat release rate and total heat release of the epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 decrease significantly compared with the values of the epoxy resin cured by NPEH720. Moreover, the curing reaction kinetics of the epoxy resin cured by DCPD‐DOPO, NPEH720 or their mixture was studied by DSC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44599.     

Synthesis and properties of trifluoromethyl groups containing epoxy resins cured with amine for low Dk materials

The study synthesized a trifluoromethyl (CF₃) groups with a modified epoxy resin, diglycidyl ether of bisphenol F (DGEBF), using environmental friendly methods. The epoxy resin was cured with 4,4′‐diaminodiphenyl‐methane (DDM). For comparison, this study also investigated curing of commercially available diglycidyl ether of bisphenol A (DGEBA) with the same curing agent by varying the ratios of DGEBF. The structure and physical properties of the epoxy resins were characterized to investigate the effect of injecting fluorinated groups into epoxy resin structures. Regarding the thermal behaviors of the specimens, the glass transition temperatures (T_g) of 50–160°C and the thermal decomposition temperatures of 200–350 °C at 5% weight loss (T_d5%) in nitrogen decreased as amount of DGEBF increased. The different ratios of cured epoxy resins showed reduced dielectric constants (D_k) (2.03–3.80 at 1 MHz) that were lower than those of pure DGEBA epoxy resins. Reduced dielectric constant is related to high electrronegativity and large free volume of fluorine atoms. In the presence of hydrophobic CF₃ groups, the epoxy resins exhibited low moisture absorption and higher contact angles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fracture and mechanical properties of epoxy resins and rubber-modified epoxy resins

Fracture and mechanical property data on a wide range of epoxy resin systems are presented. The extent to which toughening can be induced by heterophase rubber inclusions depends more on the curing agent used than on the resin component. The greatest improvements in toughness were obtained by rubber modification of epoxy resins cured with an anhydride. A preformed ABS polymer can be used to toughen many epoxy resin systems. With one major exception (where a large improvement was found) only small changes in tensile properties occur when small amounts of rubber are present.     

Low-stress encapsulants by vinylsiloxane modification

Dispersed silicone rubbers were used to reduce the stress of cresol–formaldehyde novolac epoxy resin cured with phenolic novolac resin for electronic encapsulation application. The effects of structure, molecular weight, and contents of the vinylsiloxane oligomer on reducing the stress of the encapsulant were investigated. Morphology and dynamic mechanical behavior of rubber-modified epoxy resins were also studied. The dispersed silicone rubbers effectively reduce the stress of cured epoxy resins by reducing flexural modulus and the coefficient of thermal expansion (CTE), whereas the glass transition temperature (T_g) was hardly depressed. Electronic devices encapsulated with the dispersed silicone rubber modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and have resulted in an extended device use life. © 1994 John Wiley & Sons, Inc.     

Preparation and Application of a New Curing Agent for Epoxy Resin

A new curing agent based on palmitoleic acid methyl ester modified amine (PAMEA) for epoxy resin was synthesized and characterized. Diglycidyl ether of bisphenol A (DGEBA) epoxy resins cured with different content of PAMEA along with diethylenetriamine (DETA) were prepared. The mechanical properties, dynamic mechanical properties, thermal properties, and morphology were investigated. The results indicated that the PAMEA curing agent can improve the impact strength of the cured epoxy resins considerably in comparison with the DETA curing agent, while the modulus and strength of the cured resin can also be improved slightly. When the PAMEA/epoxy resin weight ratio is 30/100, the comprehensive mechanical properties of the cured epoxy resin are optimal; at the same time, the crosslinking density and glass transition temperature of the cured epoxy resin are maximal.     

New type of phenolic resin: Curing reaction of phenol‐novolac based benzoxazine with bisoxazoline or epoxy resin using latent curing agent and the properties of the cured resin

In this study, we aimed to reduce the cure time, and to lower the cure temperature of the benzoxazine compound. Therefore, curing reaction of benzoxazine with bisoxazoline or epoxy resin using the latent curing agent and the properties of the cured resins were investigated. The cure behavior of benzoxazine with bisoxazoline or epoxy resin using the latent curing agent was monitored by differential scanning calorimetry and measurements for storage modulus (G′). The properties of the cured resin were estimated by mechanical properties, electrical insulation, water resistance, heat resistance, and flame resistance. As a result, it was confirmed that by using the latent curing agent, cure time of benzoxazine and bisoxazoline or epoxy resin was reduced, and cure temperature was lowered. And it was found that the curing reaction using phenol‐novolac based benzoxazine (Na) as the benzoxazine compound could proceed more rapidly than that using bisphenol‐A based benzoxazine (Ba) as the benzoxazine compound. However, the cured resins from Ba and bisoxazoline or epoxy resin using the latent curing agent showed good heat resistance, flame resistance, and mechanical properties compared with those from Na and bisoxazoline or epoxy resin using the latent curing agent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Epoxy resin based on 4,4′-dihydroxydiphenysulfone. I. Synthesis and reaction kinetics with 4,4′-diaminodiphenylmethane and 4,4′-diaminodiphenylsulfone

Epoxy resins based on 4,4′-dihydroxydiphenylsulfone (DGEBS) and diglycidyl ether of bisphenol A (DGEBA) were prepared by alkaline condensation of 4,4′-dihydroxydiphenylsulfone (bisphenol S) with epichlorohydrin and by recrystallization of liquid, commercial bisphenol A-type epoxy resin, respectively. Curing kinetics of the two epoxy compounds with 4,4′-diaminodiphenylmethane (DDM) and with 4,4′-diaminodiphenylsulfone (DDS) as well as T_g values of the cured materials were determined by the DSC method. It was found that the ? SO₂? group both in the epoxy resin and in the harener increases T_g values of the cured materials. DGEBS reacts with the used hardeners faster than does DGEBA and the curing reaction of DGEBS begins at lower temperature than does the curing reaction of DGEBA when the same amine is used. © 1994 John Wiley & Sons, Inc.     

Chemorheology and ultimate behavior of epoxy‐amine mixtures modified with a liquid oligomer

Rubber toughening of epoxy resins has been actively studied since the 1960s with clear progress in understanding of the ultimate properties: microstructure relationships. The morphology, obtained after curing of the modified thermosetting matrix, is a function of the process conditions as well as of the materials used because both influence the thermodynamics and the kinetics of phase separation. In this work several amounts of poly(oxypropylentriamine) (POPTA), have been added as modifier to a diglycidyl ether of bisphenol‐A (DGEBA)‐based epoxy matrix cured with a cycloaliphatic amine. Molecular weight of the neat resin and amine/epoxy stoichiometric ratio have also been used as variables. This investigation has focused upon the importance of cure chemorheology for microstructure formation by using both physicochemical (isothermal and dynamic calorimetry) and rheological techniques. In the second part of this study, the influence of the molecular weight of the epoxy resin in the ultimate properties of 15 wt % POPTA‐modified epoxy matrices is also analyzed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1269–1279, 2000     

Effect of the structure of curing agents modified by epoxidized oleic esters on the toughness of cured epoxy resins

The aim of this study was to determine the effect of the ester carbon chain length of curing agents modified by epoxidized oleic esters on the toughness of cured epoxy resins. An amine‐terminated prepolymer (i.e., curing agent G) was synthesized from a bisphenol A type liquid epoxy resin and triethylene tetramine. The toughening curing agents (G1 and G2) were prepared by reactions of epoxidized oleic methyl ester and epoxidized oleic capryl ester, respectively, with curing agent G. Fourier transform infrared spectrometry was used to characterize the chemical structure of the curing agents. The effects of the carbon chain length of the oleic ester group in the curing agents on the toughness and other performances of the curing epoxy resins were investigated by analysis of the Izod impact strength, tensile strength, elongation at break, thermal properties, and morphology of the fracture surfaces of the samples. The results denote that the toughness of the cured epoxy resins increased with the introduction of oleic esters into the curing agents without a loss of mechanical properties and that the toughness and thermal stability of the materials increased with increasing ester carbon chain length. The toughness enhancement was attributed to the flexibility of the end carbon chains and ester carbon chains of the oleic esters in the toughening curing agents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of Phenol/Formaldehyde Stoichiometry on the Modification of Epoxy Resin Using Epoxidized Novolacs

ABSTRACT

Unmodified epoxy resins based on bisphenol A exhibit brittleness and low elongation after cure. This article reports the results of a study for improving the properties of epoxy resin by blending with suitable thermosets. Hybrid polymer networks of diglycidyl ether of bisphenol A (DGEBA) resin with epoxidized phenolic novolac resins (EPN) containing phenol and formaldehyde in different stoichiometric ratios were prepared by physical blending. The modified epoxy resins were found to exhibit improved mechanical and thermal properties compared to the neat resin. DGEBA resins containing 2.5 to 20 wt% of epoxidized novolac resins (EPN) prepared in various stoichiometric ratios (1:0.6, 1:0.7, 1:08, and 1:0.9) between phenol and formaldehyde were cured using a room temperature amine hardener. The cured samples were tested for mechanical properties such as tensile strength, modulus, elongation, and energy absorption at break. All the EPNs are seen to improve tensile strength, elongation, and energy absorption at break of the resin. The blend of DGEBA with 10 wt% of EPN-3 (1:0.8) exhibits maximum improvement in strength, elongation, and energy absorption. EPN loading above 10 wt% is found to lower these properties in a manner similar to the behavior of any filler material. The property profiles of epoxy–EPN blends imply a toughening action by epoxidized novolac resins and the extent of modification is found to depend on the molar ratio between phenol and formaldehyde in the novolac.     

Studies on isotactic poly(phenyl glycidyl ether)‐modified epoxy resins. II. Toughening of epoxy resins

A semicrystalline polymer, isotactic poly(phenyl glycidyl ether) (i‐PPGE) was used as a modifier for epoxy resin; 1,8‐Diamino‐p‐methane (MNDA) and 4,4′‐Diamino diphenyl sulfone (DDS) were used as curing agents. In the MNDA‐cured resins, the dispersed phase were spherical particles with diameters in the range of 0.5–1.0 μm when the resin was blended with 5 phr i‐PPGE. In the DDS‐cured resins, the particle size distribution of the dispersed phase was much wider. The difference was traced back to the reactivity of the curing agent and the different regimes used for curing. Through dynamic mechanical analysis, it was found that in the MNDA‐cured systems, i‐PPGE had a lower crystallinity than in the DDS‐cured system. In spite of the remarkable difference in the morphology and microstructure of the modified resins cured with these two curing agents, the toughening effects of i‐PPGE were similar for these resins. The critical stress intensity factor (K_IC) was increased by 54% and 53%, respectively, for the resins cured by DDS and by MNDA, blending with 5 phr of the toughner. i‐PPGE was comparable with the classical toughners carboxyl‐terminated butadiene‐acrylonitrile copolymers in effectiveness of toughening the epoxy resin. An advantage of i‐PPGE was that the modulus and the glass‐transition temperature of the resin were less affected. However, this modifier caused the flexural strength to decrease somewhat. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1223–1232, 2002; DOI 10.1002/app.10445     

Toughening of epoxy resins by modified m-phenylene diamine having soft ether chain

A new soften curing agent for toughening epoxy resins was synthesized by m-phenylene diamine modified with epoxypropyl butyl ether. The curing processes of epoxy resin/modified m-phenylene diamine were traced by differential scanning calorimetry (DSC), then kinetic parameters, ΔE and n, were deduced. Fourier transform infrared (FTIR) analysis showed that the longer the reaction time was, the smaller the absorption peaks of epoxy group were. The results of the mechanical properties demonstrated that the impact property of the epoxy resin cured by modified m-phenylene diamine at the moderate temperature was better than that of cured by unmodified one because of the introduction of soft ether chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and properties of fluorinated biphenyl‐type epoxy resin

A novel fluorinated biphenyl‐type epoxy resin (FBE) was synthesized by epoxidation of a fluorinated biphenyl‐type phenolic resin, which was prepared by the condensation of 3‐trifluoromethylphenol and 4,4′‐bismethoxymethylbiphenyl catalyzed in the presence of strong Lewis acid. Resin blends mixed by FBE with phenolic resin as curing agent showed low melt viscosity (1.3–2.5 Pa s) at 120–122°C. Experimental results indicated that the cured fluorinated epoxy resins possess good thermal stability with 5% weight loss under 409–415°C, high glass‐transition temperature of 139–151°C (determined by dynamic mechanical analysis), and outstanding mechanical properties with flexural strength of 117–121 MPa as well as tensile strength of 71–72 MPa. The thermally cured fluorinated biphenyl‐type epoxy resin also showed good electrical insulation properties with volume resistivity of 0.5–0.8 × 10¹⁷ Ω cm and surface resistivity of 0.8–4.6 × 10¹⁶ Ω. The measured dielectric constants at 1 MHz were in the range of 3.8–4.1 and the measured dielectric dissipation factors (tan δ) were in the range of 3.6–3.8 × 10^?3. It was found that the fluorinated epoxy resins have improved dielectric properties, lower moisture adsorption, as well as better flame‐retardant properties compared with the corresponding commercial biphenyl‐type epoxy resins. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

New thermosetting resin from terpenediphenol‐based benzoxazine and epoxy resin

Terpenediphenol‐based benzoxazine was prepared from terpenediphenol, formaline, and aniline. Curing behavior of the benzoxazine with epoxy resin and the properties of the cured resin were investigated. Consequently, the curing reaction did not proceed at low temperatures, but it proceeded rapidly at higher temperatures without a curing accelerator. The properties of the cured resin both from neat resins and from reinforced resins with fused silica were evaluated, respectively. The cured resins showed good heat resistance, mechanical properties, electrical insulation, and especially water resistance, compared with the cured resin from bisphenol A type novolac and epoxy resin. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2266–2273, 1999     

Synthesis of rosin‐based flexible anhydride‐type curing agents and properties of the cured epoxy

BACKGROUND: Although rosin acid derivatives have received attention in polymer synthesis in recent years, to the best of our knowledge, they have rarely been employed as epoxy curing agents. The objective of the study reported here was to synthesize rosin‐based flexible anhydride‐type curing agents and demonstrate that the flexibility of a cured epoxy resin can be manipulated by selection of rosin‐based anhydride‐type curing agents with appropriate molecular rigidity/flexibility. RESULTS: Maleopimarate‐terminated low molecular weight polycaprolactones (PCLs) were synthesized and studied as anhydride‐type curing agents for epoxy curing. The chemical structures of the products were confirmed using ¹H NMR spectroscopy and Fourier transform infrared spectroscopy. Mechanical and thermal properties of the cured epoxy resins were studied. The results indicate that both the epoxy/anhydride equivalent ratio and the molecular weight of PCL diol play important roles in the properties of cured resins. CONCLUSION: Rosin‐based anhydride‐terminated polyesters could be used as bio‐based epoxy curing agents. A broad spectrum of mechanical and thermal properties of the cured epoxy resins can be obtained by varying the molecular length of the polyester segment and the epoxy/curing agent ratio. Copyright © 2009 Society of Chemical Industry