Multifunctional epoxy resins

The curing behavior of epoxy resins prepared by reacting epichlorohydrin with 4,4′-diaminodiphenyl methane (DADPM)/4,4′-diaminodiphenyl ether (DADPE) or 4,4′-diaminodiphenyl sulfone (DDS) was investigated using DDS and tris-(m-aminophenyl)phosphine oxide (TAP) as curing agents. A broad exothermic transition with two maxima were observed in the temperature range of 100–315°C when TAP was used as the curing agent. The effect of varying DDS concentration on curing behavior of epoxy resin was also investigated. Peak exotherm temperature (T_exo) decreased with increasing concentration of DDS, whereas heat of curing (ΔH) increased with an increase in amine concentration up to an optimum value and then decreased. Thermal stability of the resins, cured isothermally at 200°C for 3 h, was investigated using thermogravimetric analysis in a nitrogen atmosphere. Glass fiber-reinforced multifunctional epoxy resin laminates were fabricated and the mechanical properties were evaluated. © 1993 John Wiley & Sons, Inc.     

Dynamic mechanical experiments for probing process-structure-property relations in amine-cured epoxies

Dynamic mechanical experiments were performed on an amine-cured high performance epoxy system containing two types of epoxies and one amine. The system approximates a commercial resin system used widely as matrix material for graphite composites and whose main ingredients and composition are 88.5 percent of tetraglycidyl 4,4′-diamino diphenyl methane (TGDDM) and 11.5 percent of polyglycidyl ether of Bisphenol A Novalac epoxy with varying compositions of 4,4′-diaminodiphenyl sulfone (DDS), ranging from 19 to 40 PHR. Specifically, the effects of DDS and Novalac content as well as processing conditions including the particle size of solid components, the mixing speed, mixing temperature, and the mixing duration of the components on the dynamic mechanical properties of the epoxy polymer were investigated. A viscoelastic transition in the dynamic spectrum which was observed to be quite sensitive to the sample's T_g in conjunction with incomplete crosslinking reactions allowed for interrelating the composition and processing variables to the structure and bulk properties of this epoxy system.     

Modification and compatibility of epoxy resin with hydroxyl-terminated or amine-terminated polyurethanes

Phenolic hydroxyl-terminated (HTPU) and aromatic amine-terminated (ATPU) PU modifiers were prepared by reacting two different macroglycols (PTMG, polytetramethylene glycol, M_n = 2000, and PBA, Polybutylene adpate, M_n = 2000) with 4,4′-diphenylmethane diisocyanate (MDI), then further coupling with two different coupling agents, bisphenol A or 4,4′-diaminodiphenyl sulfone (DDS). These four types of PU prepolymers were used to modify the epoxy resin with 4,4′-diamino-diphenyl sulfone as a curing agent. From the experimental results, it was shown that the values of fracture energy, G_IC, for PU-modified epoxy were dependent on the macroglycols and the coupling agents. Scanning electron microscopy (SEM) revealed that the ether type (PTMG) of PU-modified epoxy showed the presence of an aggregated separated phase, which varied between 0.5 μm and 4 μm in the ATPU (PTMG) and between 1 μm and 1.5 μm in HTPU (PTMG) modified system. On the contrary, the ester type (PBA) PU-modified epoxy resin showed a homogeneous morphology and consequently a much smaller effect on toughening for its good compatibility with the epoxy network. In addition, it was found that the hydroxyl-terminated bisphenol A as a coupling agent improved fracture toughness more than the amine-terminated DDS because of effective molecular weight buildup by a chain extension reaction. The glass transition temperature (T_g) of modified epoxy resin as measured by dynamic mechanical analysis (DMA) was lower in PTMG-based PU than in a PBA-based PU series with the same weight of modifier.     

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.     

Properties of epoxy nanoclay system based on diaminodiphenyl sulfone and diglycidyl ether of bisphenol F: influence of post cure and structure of amine and epoxy

Materials were prepared with Cloisite 30B, diglycidyl ether of bisphenol F and diaminodiphenyl sulfone (DDS) to investigate the relationship between exfoliation and property enhancement. A higher level of exfoliation was found with 4,4′‐DDS than in the material cured with 3,3′‐DDS. The material with 4,4′‐DDS that exhibited a higher degree of exfoliation also resulted in larger improvements in physical properties with nanoclay. Increasing the ratio of trifunctional to difunctional epoxy led to a significant decrease in the level of clay dispersion. Increasing the ratio of trifunctional epoxy in the nanocomposite also caused a decrease in T_g with the addition of nanoclay. However, an increase in T_g with increasing clay loadings was detected in samples with a higher degree of exfoliation, with only difunctional epoxy. Similar behaviour was found for samples with and without a post cure. Excessive post cure led to a decrease in thermal stability in Cloisite 30B‐containing samples. Copyright © 2007 Society of Chemical Industry     

Synthesis, characterization and properties of tetramethyl stilbene-based epoxy resins for electronic encapsulation

Two novel tetramethyl stilbene-based novolac (II and IV) were synthesized from 2,6-dimethyl phenol and chloroacetaldehyde dimethylacetal or chloroacetone, and then the resulted novolacs were epoxidized to tetramethyl stilbene-based epoxy resins (III and V). The proposed structures were confirmed by FTIR, elemental analysis, mass spectra, NMR spectra and epoxy equivalent weight titration. The synthesized tetramethyl stilbene-based epoxy resins were cured with 4,4-diaminodiphenyl methane (DDM) and 4,4-diaminodiphenyl sulfone (DDS). Thermal properties of cured epoxy resins were studied using dynamic mechanical analyzer, differential scanning calorimeter, thermal expansion analyzer and thermal gravimetric analyzer (TGA). These data were compared with that of the commercial tetramethyl biphenol (TMBP) epoxy system. According to the experimental data, the order of T_g for cured epoxy system is III>TMBP>V. The order of moisture absorption for cured epoxy system is V<III<TMBP. According to TGA, the 5% degradation temperatures in nitrogen atmosphere were in the range 370-377 and 397-412 °C for DDM and DDS curing systems, respectively. In air atmosphere, the 5% degradation temperatures were in the range 372-385 and 410-411 °C for DDM and DDS curing systems, respectively. The CTE is in inverse order with T_g, therefore, III/DDS<TMBP/DDS<V/DDS.     

High performance epoxy resins cured in the presence of BF3 catalyst

Dynamic mechanical experiments have been conducted on an epoxy system made with tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) and polyglycidyl ether of Bisphenol A Novalac that were cured with 4,4′-diaminodiphenyl sulfone (DDS) in the presence of Boron trifluoride monoethylamine catalyst (BF₃:EtNH₂). As the concentration of BF₃:EtNH₂ increased, the low temperature β-transition magnitude increased slightly. The α₁-transition observed in the uncatalyzed system decreased significantly with the addition of BF₃:EtNH₂ catalyst. The α₂ or glass transition temperature of this system increased with increasing catalyst concentration. Both the catalyzed and uncatalyzed epoxy formulations studied in this work are important due to their similarity to systems used commercially in epoxy matrix composites.     

CURING KINETICS AND THERMAL PROPERTY CHARACTERIZATION OF BISPHENOL-F EPOXY RESIN AND DDS SYSTEM

The curing kinetics of bisphenol-F epoxy resin (BPFER)/4,4′-diaminodiphenyl sulfone (DDS) system were studied by isothermal experiments using a differential scanning calorimeter (DSC). Autocatalytic behavior was shown in the first stages of the cure for the system, which could be well described by the model proposed by Kamal that includes two rate constants, k ₁ and k ₂, and two reaction orders, m and n. The curing reaction at the later stages was practically diffusion-controlled due to the onset of gelation and vitrification. To consider the diffusion effect more precisely, diffusion factor, f(α), was introduced into Kamal's equation. Thus, the curing kinetics could be predicted well over the whole range of conversion covering both pre- and postvitrification stages. The glass transition temperatures (T_gs) of the BPFER/DDS system isothermally cured partially were determined by means of torsional braid analysis (TBA), and the results showed that T_gs increased with conversion up to a constant value. The highest T_g was 406.2 K. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis (TGA), revealing two decomposition steps.     

Characterization of the cure of TGDDM/DDS epoxy resins by chemiluminescence I. Spectral and thermal analysis

The emission of weak visible chemiluminescence (CL) during the cure of a tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM)-based epoxy resin, with three different concentrations of 4,4′-diaminodiphenylsulfone (DDS) has been studied at 135°C. Spectral analysis indicates that the CL originates from trace oxidation of the TGDDM resin and the emission intensity is sensitive to the viscosity changes during cure. From thermal analysis data, sharp discontinuities in CL intensity are shown to occur at the gel point. The temperature dependence of CL from a cured resin also shows a sharp discontinuity at T_g. These results indicate that CL provides a sensitive monitor of both the kinetics of gelation and the network formation in this epoxy resin.     

Chemical reactions,thermal and mechanical properties of epoxy — Polycarbonate blends cured with aromatic amines

Bisphenol-A polycarbonate (PC) has been incorporated into epoxy resin cured with 4,4-diaminodiphenyl sulphone (DDS) and 4,4'-diaminodiphenyl methane (DDM). IR spectra reveal that transesterification and transamidation occur between the carbonate group of PC and the hydroxyl group of cured epoxy resin for the DDM-cured system, and that only transesterification occurs for the DDS-cured system. Scanning electron micrographs (SEM) show no evidence of phase separation in these cured systems, which is an indication of full miscibility between the bisphenol-A monomers and PC-oligomers with the copolymer network. The mechanical strength and glass transition temperature (T_g) fluctuate with PC content, whereas the flexural modulus shows a steadily increasing tendency.     

Synthesis, characterization, and properties of novel novolac epoxy resin containing naphthalene moiety

A series of novel novolac epoxy resins containing naphthalene moiety with different molecular weights were synthesized via condensation of bisphenol A and 1-naphthaldehyde, followed by epoxidation with epichlorohydrin. The chemical structure of the naphthalene epoxy thus obtained was characterized using FTIR, ¹H NMR spectra and GPC analyses. The naphthalene epoxy was cured with 4,4′-diaminodiphenyl sulfone (DDS) and the cured products were characterized with thermogravimetric analysis, dynamic mechanical analysis, and X-ray diffraction. Compared with the diglycidyl ether of bisphenol A (DGEBA), the cured naphthalene epoxy resin showed remarkably higher glass transition temperatures (T_gs), enhanced thermal stability and better moisture resistance. When the molar ratio of 1-naphthaldehyde to bisphenol A was 0.67, the optimal thermal resistance was observed.     

Epoxy thermosetting systems: Dynamic mechanical analysis of the reactions of aromatic diamines with the diglycidyl ether of bisphenol A

Dynamic mechanical behavior during the reactions of four aromatic diamines (m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfone, and benzidine) with the diglycidyl ether of bisphenol A was studied by torsional braid analysis under isothermal conditions. Depending on the cure temperature, three types of behavior were observed: (I) below T_gg (the glass transition temperature of the reactive systems at the gel point); (II) between T_gg and T_g∞ (the glass transition temperature of the ultimately cured polymers); (III) above T_g∞. Overall activation energies and apparent overall rate constants of the cure reactions based on third-order overall kinetics were determined before gelation, after gelation but before vitrification, and after vitrification, using gelation time, relative rigidity, and glass transition temperature T_g(t) of the polymers as kinetic terms. The influence of cure temperature and structure of the diamines on the kinetic parameters is discussed.     

Phase separation of poly(ether sulfone imide) modified epoxy resin

Poly(ether sulfone imide)s (PEI) with molecular weight M_n ∼ 10⁴ were synthesized from 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and amine terminated poly(ether sulfone) having molecular weights ranging from M_n ∼ 400 to M_n ∼ 4000. Thus, the PEIs had the same molecular weight but various imide and ether sulfone contents. The PEIs were mixed with a stoichiometric mixture of diglycidyl ether bis-phenol-A (DGEBA)/diamino diphenyl sulfone (DDS). The effect of PEI on the curing reaction of DGEBA/DDS and the morphology of the polymer blend were studied by differential scanning calorimetry (DSC) and optical microscopy. In the DGEBA/DDS/PEI blend with a fixed PEI molecular weight and PEI concentration but with various imide content, the experimental data revealed the PEI with a higher content of ether sulfone had a lower T_g and a better compatibility with solvents and epoxy resins; the curing reaction rate of DGEBA/DDS/PEI was faster for PEI with a higher imide content; the DSC data of cured DGEBA/DDS/PEI showed two T_gs, indicating phase separation between PEI and cured epoxy resins; and the data of optical microscopy showed that the compatibility of PEI with epoxy resins increased with the content of ether sulfone in PEI. © 1996 John Wiley & Sons, Inc.     

Morphology,thermal and mechanical performance of epoxy/polysulfone composites improved by curing with two different aromatic diamines

Epoxy/polysufone (PSF) composites cured with 4,4'-diaminodiphenyl sulfone (DDS) and 4,4'-diaminodiphenyl methane (DDM) were fabricated, and the effect of dual curing reaction of diamines with epoxy on morphology, mechanical, and thermal performance was investigated. DSC results indicated that DDM was more reactive than DDS and the activation energy decreased with the rising of DDM content. Structures with small domain size at the early stage of phase separation were fixed by the fast epoxy-DDM reaction. When the DDM content was elevated to a high level, large dual structures were changed to fine bicontinuous structures, which was favorable to improve the mechanical property. The mechanical performance of epoxy composites was enhanced and the maximum values were achieved when the DDM/DDS ratio was located at 75/25 (PSF/DDS0.25-DDM0.75). The flexural and tensile strength relative to epoxy/DDM system were enhanced more than those relative to epoxy/DDS, while the increase in toughness was the opposite. TGA measurement showed that thermal stability of epoxy/PSF composites was improved because of the restricting effect of continuous PSF domains on thermal motion of epoxy. DMA analysis exhibited two relaxation peaks for PSF/DDS0.25-DDM0.75, which could be attributed to the formation of phase separated morphology and epoxy network with different cross-link density.     

Toughening of epoxy resin by reacting with functional terminated-polyurethanes

Hydroxyl-, amine-, and anhydride-terminated polyurethane (PU) prepolymer which were synthesized from polyether (PTMG) diol, 4,4′-diphenylmethane diisocyanate (MDI), and a coupling agent bisphenol-A, 4,4′-diaminodiphenyl sulfone (DDS), or benzophenonetetracarboxylic dianhydride (BTDA) were used to modify the toughness of bisphenol-A diglycidyl ether epoxy resin (DGEBA) cured with 4,4′-diaminodiphenyl sulfone. From the experimental results, it was shown that the modified resin displayed a significant improvement in fracture energy (G_IC) and also in its interfacial shear strength with polyaramid fiber. It was more enhanced with increase of the PU modifier wt % content. The hydroxyl-terminated PU was found to be the most effective among those three prepolymers. In addition, the toughening mechanism was discussed based on the morphological and the dynamic mechanical behavior of the modified epoxy resin. Fractography of the specimen observed by transmission (TEM) and scanning electron microscopy (SEM) revealed that the modified resin had a two-phase structure. The existence of an unclean fiber surface after its fiber pullout test suggested that a ductile fracture might have occurred. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of novel phosphorus‐containing bismaleimide/epoxy resins

A novel soluble phosphorus‐containing bismaleimide (BMI) monomer, bis(3‐maleimidophenyl)phenylphosphine oxide (BMIPO), was synthesized by the imidization of bis(3‐aminophenyl) phenylphosphine oxide, in which its structural characterization was identified with ¹H‐NMR, ¹³C‐NMR, and Fourier transform infrared spectra. The BMIPO resin, with five‐membered imide rings and high phenyl density, was an excellent flame retardant with a high glass‐transition temperature (T_g), onset decomposition temperature, and limited oxygen index. In phosphorus‐containing BMI/epoxy/4,4′‐methylene dianiline (DDM)‐cured resins, homogeneous products were obtained from all proportions without phase separation. Because of the higher reactivity of BMIPO/DDM relative to that of 4,4′‐bismaleimidodiphenylmethane (BMIM)/DDM, the increase in the BMIPO/BMIM ratio in this blending resin increased the recrosslinking hazards of the postcuring stage and so lowered the T_g value and thermal stability. The thermal stability of the BMI/epoxy‐cured system was lower than that of the epoxy‐cured system because of the introduction of a phosphide group into BMIPO, whereas for the T_g value and flame retardancy, the former was significantly higher than the latter: the higher the BMIPO content in the blend, the higher the flame retardancy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2080–2089, 2002; DOI 10.1002/app.10607     

Novel effect of barbituric acid on glass transition temperature of bismaleimide–epoxy resin systems

Barbituric acid (BTA) has a novel influence on glass transition temperature (T_g) of bismaleimide (BMI)–epoxy resin systems. It causes the T_g of a BMI–epoxy resin system to rise significantly. The BTA's influence on T_g was investigated by changing the molar ratio of the reactants. In addition, the influence of benzoperoxide (BPO) on T_g was compared with that of BTA. The reaction selectivity of BTA and diamino-diphenyl sulfone (DDS) toward BMI and epoxy individually in the BMI–epoxy blended systems were studied using the DSC and GPC. By controlling the amount of DDS and BTA, epoxy and BMI could form intercrosslinking networks.     

Isothermal Cure of an Epoxy System Containing Tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM), a Multifunctional Novolac Glycidyl Ether and 4,4′-Diaminodiphenylsulphone (DDS): Vitrification and Gelation

Times to gelation and vitrification have been determined at different isothermal curing temperatures between 200 and 240°C for an epoxy/amine system containing both tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and a multifunctional Novolac glycidyl ether with 4,4′-diaminodiphenylsulphone (DDS). The mixture was rich in epoxy, with an amine/epoxide ratio of 0·64. Gelation occurred around 44% conversion. Vitrification was determined from data curves of glass transition temperature, T_g, versus curing time obtained from differential scanning calorimetry experiments. The minimum and maximum values T_g determined for this epoxy system were T_g0=12°C and T_gmax=242°C. Values of activation energy for the cure reaction were obtained from T_g versus time shift factors, a_T, and gel time measurements. These values were, respectively, 76·2kJmol^-1 and 61·0kJmol^-1. The isothermal time–temperature–transformation (TTT) diagram for this system has been established. Vitrification and gelation curves cross at a cure temperature of 102°C, which corresponds to glass transition temperature of the gel. © of SCI.     

Cure and glass transition temperature of the bisphenol S epoxy resin with 4,4′‐diaminodiphenylmethane

The curing reaction of bisphenol S epoxy resin (BPSER) with 4,4′‐diaminodiphenylmethane (DDM) was studied by means of torsional braid analysis (TBA) in the temperature range of 393–433 K. The glass transition temperature (T_g) of the BPSER/DDM system is determined, and the results show that the reaction rate increases with increasing the T_g in terms of the rate constant, but decreases with increasing conversion. 1 The T_g of BPSER/DDM is about 40 K higher than BPAER/DDM. The gelation and vitrification time were assigned by the isothermal TBA under 373 K; in addition, an FTIR spectrum was carried out to describe the change of the molecular structure. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of the BPSER/DDM has n‐order reaction kinetics. 2 © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 794–799, 2000     

Hygrothermal Aging Effects in Cured Epoxies

The effect of relatively severe hygrothermal aging on the sorption and also the diffusion of water at 40°C has been studied for a number of epoxy networks comprising tetraglycidyl 4,4′-diaminodiphenyl methane, and the curing agent 4,4′-diaminodiphenyl sulphone, 4,4′-diaminodiphenyl methane and 2,2′-dichloro-4,4′-diaminodiphenyl methane. Aging at high temperatures is accompanied by a pronounced increase in sorptive capacity at 40°C consistent with a significant expansion of the network. Dry annealing of the aged network at sub- T_g temperatures collapses the expanded structure to recover the sorptive capacity of the unaged network. Preliminary studies of the sorption-desorption kinetics for aged networks indicate that the effective diffusion coefficient is not markedly affected.