Synthesis of Tri‐Aryl Methane Epoxy Resin Isomers and Their Cure with Aromatic Amines

In this work, two tri‐aryl and one bi‐aryl epoxy resin, bis[(glycidyloxy)phenyl)]‐m‐xylene (BGOPmX), bis[(glycidyloxy)phenyl)]‐p‐xylene (BGOPpX), and bis(glycidyloxy) biphenyl (BGOBP) are synthesized and cured with methylene dianiline and 4,4′‐diamino diphenyl sulfone. Structure, property, and processing relationships are investigated and compared against diglycidyl ether of bis‐phenol F epoxy resin to better understand the impact of rigid and flexible subunits within the network structure. The rigid BGOBP epoxy network has a higher yield strain, and displays the highest glass transition temperature and a higher coefficient of thermal expansion (CTE) regardless of amine. Conversely, the more flexible tri‐aryl epoxy resins, BGOPmX and BGOPpX, have higher moduli and lower CTE. Properties such as yield stress and thermal degradation are relatively unaffected by structure. Results where possible are discussed in terms of the likely equilibrium packing density of the network and short range and segmental motions of the polymer networks determined from sub‐ambient dynamic mechanical analysis. Differences between BGOPmX and BGOPpX highlight the effect of minor variations in structure on reactivity, glass transition temperature, and compressive properties. This work clearly illustrates how fine control of chemical structure can tune the mechanical and thermal properties and reaction kinetics of network polymers.     

Subtle variations in the structure of crosslinked epoxy networks and the impact upon mechanical and thermal properties

Presented here is an investigation of the structure–property relationships of crosslinked networks using three bi-functional glycidyl ether aromatic epoxy resins, two bi-aryl and one tri-aryl, cured with bi- and tri-aryl amines. Subtle changes to the monomer chemistry including changing aromatic substitution patterns from meta to para, methylene to isopropyl and isopropyl to ether were explored. Changing an epoxy resin backbone from methylene to isopropyl enhances backbone rigidity thus increasing glass transition temperature (T_g), yield strength, and strain despite reducing modulus. Changing meta-substitution to para increases T_g and yield strain while leaving strength unaffected and reducing modulus. Changing isopropyl linkages to ether reduces modulus, strength, T_g, and yield strain reflecting increased molecular flexibility. Using three instead of two aromatic rings increases the molecular weight between crosslinks thereby decreasing T_g and yield strain while increasing modulus and strength. Despite the complexities of multiple systems for varying epoxy resins and amine hardeners, the effect upon network properties is explained in terms of short- and long-range molecular and segmental mobility, crosslink density, and equilibrium packing density. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48874.     

Synthesis and reactivity of Mannich-derived polyoxyethylene amines as epoxy curing agents

The facile Mannich reaction of phenol, formaldehyde, and polyoxyalkylene polyamines at various molar ratios afforded a family of polyetheramines containing functionalities of phenol, primary amines, secondary amines, and polyoxyethylene or polyoxypropylene block copolymers in the same molecule. The synthesis can be generalized by using various polyoxyethylene or polyoxypropylene diamines (and triamines) of molecular weights ranging from 104 to 430 to prepare a family of Mannich amines, with exception of certain gel products such as phenol/formaldehyde/bis(aminoethyl)ether adduct at 1 : 3 : 3 molar ratio. The series of Mannich amines were evaluated for their epoxy curing reactivities by comparing their gel time and drying time. The Mannich amines prepared from polyoxyethylene amines exhibited higher reactivities than those of polyoxypropylene amine derivatives. The trend of their relative reactivities is explained by the molecular size, the multiplicity of amines in the molecule, and the steric hindrance of amine structure. The physical properties of cured epoxy materials, such as impact, tensile, flexural strength, and hardness properties were also measured and correlated with the amine molecular weight, crosslinking density, and the presence of phenol group. The structure–property relationship is discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2339–2346, 1997     

Influence of amine-terminated additives on thermal and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) cured epoxy

The present work accounts for the influence of aromatic amide oligomers on the inherent brittleness of cured epoxy. Aromatic and aliphatic amine-terminated amide oligomers have been prepared by condensation polymerization using isophthaloyl dichloride and two different amines. The oligomers have been characterized using Fourier transform infrared spectroscopy and wide angle X-ray diffraction analysis. Diglycidyl ether of bisphenol A (DGEBA) is cured with a diamine (4,4′-oxydianiline) by using different weight ratio of oligomers. The FTIR of cured epoxy shows ring opening by the disappearance of oxirane ring peak at 913 cm⁻¹, whereas X-ray diffraction shows its amorphous phase in the cured state. The thermogravimetric analysis of the resultant composites shows that the thermal stability slightly decreases (467–454 °C) with increasing the oligomer content from 5 to 25 wt %, whereas the mechanical parameters (Young's modulus, tensile strength, impact strength, and elongation at break) increase with increase in the oligomer content. DMA shows lower tanδ values for aliphatic amine-terminated oligomers for cured epoxy. Two-phase surface morphology is observed through scanning electron microscopy. Owing to their high mechanical and thermal properties, aromatic amides have observed to greatly influence the mechanical properties of cured epoxy, particularly its brittleness. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48404.     

Effect of structure of aromatic diamines on curing characteristics,thermal stability,and mechanical properties of epoxy resins. I

The curing behavior of diglycidyl ether of bisphenol-A (DGEBA) with aromatic diamines having aryl–ether, aryl–ether–carbonyl, and aryl–ether–sulfone linkages was studied using differential scanning calorimetry (DSC). Aromatic diaminessuch as 1,3-bis(aminophenoxy)benzene (R), 1,4-bis(aminophenoxy)benzene (H),2,2′-bis[4-(4-aminophenoxy)phenyl]propane (B), 4,4′-bis(4-aminophenoxy)benzo-phenone (P), and bis[4-(4-aminophenoxy)phenyl]sulfone (S) were synthesized and characterized in the laboratory. Curing of DGEBA was done using both stoichiometric and nonstoichiometric amounts of diamines and the reaction was monitored using DSC. The reactivity of the diamines depended on the structure. The presence of electron withdrawing groups, even though significantly apart from the reaction site, reduced the nucleophilicity. No significant change was observed in the activation energy for curing, which was around 56 ± 2 kJ/mol. The glass transition temperature of the epoxy network depended on the structure and was higher when diamines P and S were used in comparison to diamines R, H, and B. The cured resins were stable up to 300°C, and maximum char yield (i.e., 32% at 600°C) was obtained in DGEBA cured with diamine P. The room temperature mechanical properties only changed marginally with the structure of the diamines. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1759–1766, 1998     

Development of epoxy-cyanate ester-clay nanocomposites offering enhanced thermally stability

The preparation and characterization of blends of a series of dicyanate monomers such as 2,2′-bis(4-cyanatophenyl) propane (DCDPP), bis-4-cyanato-biphenyl (DCBP), bis-4-cyanatonaphthalene (DCN), 3,3′-bis(4-cyanatophenyl)sulphide (DCTDP), 3,3′-bis(4-cyanatophenyl)sulphone (DCDPS), and the diglycidyl ether of bisphenol A are reported. These copolymers are combined with a montmorillionite nanoclay and both epoxy-cyanate blends and epoxy-cyanate blends-nanoclay composites are all analyzed for thermal stability, thermal degradation kinetics, flame retardancy, and impact strength. The nanocomposites are further characterized by X-ray diffraction and SEM to determine morphological features, from which structure–property relationships are determined. Dispersion of the nanoclay is of paramount importance, but its inclusion serves to improve char yield and impact strength, when this is achieved. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47754.     

Toughened cycloaliphatic epoxy resin for demanding thermal applications and surface coatings

An epoxy resin based on nonglycidyl ether and varying content of carboxyl‐terminated (poly)butadiene acrylonitrile copolymer was cured using an aromatic amine hardener. The ultimate aim of the study was to modify the brittle epoxy matrix by the liquid rubber to improve toughness characteristics. Fourier transform infrared spectroscopic analysis of the modified was performed to understand the structural transformations taking place during the uncured and cured stage of the modified systems. The decreasing trend in exothermal heat of reaction with increasing rubber content in the epoxy resin can be explained by the fact that the increase of carboxyl‐terminated butadiene acrylonitrile copolymer (CTBN) modifier might induce a high reactivity of the end groups with the epoxide ring and resulting shorter curing times and, hence, the faster curing process than the unmodified resin. Tensile strength, impact strength, and elongation‐at‐break behaviors of neat as well as modified networks have been studied to observe the effect of rubber modification. Blends sample exhibits better properties as compared to pure epoxy resin in terms of increase in impact strength and elongation‐at‐break of the casting and gloss, scratch hardness, adhesion, and flexibility of the film. The improvement in these properties indicate that the rubber‐modified resin would be more durable than the epoxy based on di glycidyl ether of bis‐phenol‐A and other epoxies. The films of coating based on epoxy with 15 wt % CTBN offered the maximum resistance toward different concentrations of acids, alkalies, and solvents as compared to the cured films of other blend samples. The thermal stability of the cycloaliphatic‐based epoxy resin was increased with the addition of 15 wt % CTBN in epoxy matrix. Cycloaliphatic‐based epoxy network modified with CTBN displayed two phase separated morphology with dispersed rubber globules in the matrix resin, i.e., they revealed the presence of two phase morphological features. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Curing kinetics and mechanical properties of fast curing epoxy resins with isophorone diamine and N-(3-aminopropyl)-imidazole

Fast curing epoxy resins were prepared by the reactions of diglycidyl ether of bisphenol A with isophorone diamine (IPD) and N-(3-aminopropyl)-imidazole (API), and their curing kinetics and mechanical properties influenced by IPD content were also investigated. The analysis of curing kinetics was based on the nonisothermal differential scanning calorimetry (DSC) data with the typical Kissinger, Ozawa, and Flynn–Wall–Ozawa models, respectively. The glass-transition temperature was also measured by the same technique. Additionally, the mechanical properties including flexural, impact, and tensile performances were tested, and the curing time was estimated by isothermal DSC. The degree of cure (α) dependency of activation energy (E_a ) revealed the complexity of curing reaction. Detailed analysis of the curing kinetics at the molecular level indicated that the dependence of E_a on the α was a combined effect of addition reaction, autocatalytic reaction, viscosity, and steric hindrance. From the nonisothermal curves, the curing reaction mechanism could be proposed according to the increasingly obvious low temperature peaks generated by the addition reaction of epoxy group with the primary amines in API and IPD molecules. Using the preferred resin formulation, the resin system could be cured within 10 min at 120 °C with a relatively good mechanical performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47950.     

Thermoplastic and moisture-dependent behavior of lignin phenol formaldehyde resins

Bonding kinetics of thermosetting adhesives is influenced by a variety of factors such as temperature, humidity, and resin properties. A comparison of lignin-based phenol formaldehyde (LPF) and phenol formaldehyde (PF) adhesive in terms of reactivity and mechanical properties referring to testing conditions (temperature, moisture of specimen) were investigated. For this purpose, two resins were manufactured aiming for similar technological resin properties. The reactivity was evaluated by B-time measurements at different temperatures and the development of bonding strength at three different conditions, testing immediately after hot pressing, after applying a cooling phase after hot pressing, or sample conditioning at standard climate. In addition, the moisture stability of the two fully cured resins was examined. The calculated reactivity index demonstrated that LPF requires more energy for curing than PF. Further results indicate that lignin as substituent for phenol in PF resin has a negative impact on its moisture resistance. Additionally, the known thermoplastic behavior of lignin could also be detected in the behavior of the cured resin. This behavior is relevant for the adhesive in use and necessitates a cooling phase before testing the bonding strength development of lignin-based adhesive systems. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48011.     

Effect of structure of aromatic imide–amines on curing behavior and thermal stability of diglycidyl ether of bisphenol‐A

The curing behavior of diglycidyl ether of bisphenol‐A (DGEBA) with aromatic imide–amines having aryl ether, sulfone, and methylene linkages was studied using differential scanning calorimetry (DSC). Six imide–amines of varying structure were synthesized by reacting 1 mol of naphthalene 1,4,5,8‐tetracarboxylic dianhydride (N) or 4,4′‐oxodiphthalic anhydride (O) with excess (>2 mol) of 4,4′‐diaminodiphenylether [E] or 4,4′‐diaminodiphenyl methane [M] or 4,4′‐diaminodiphenyl sulfone [S]. The imide–amines prepared by reacting O or N with S, M, and E have been designated as OS/NS; OM/NM, and OE/NE, respectively. Structural characterization of imide–amines was done using FTIR, ¹H NMR, ¹³C NMR, and elemental analysis. The curing behavior of DGEBA in the presence of stoichiometric amount of imide–amines was investigated by recording DSC scans. A broad exothermic transition was observed and the peak exotherm temperature was found to be dependent on the structure of imide–amines. The peak exotherm temperature (T_p) was lowest in case of imide–amines OE and highest in case of imide–amines NS/OS. Thermal stability of isothermally cured DGEBA in the presence of imide–amines was evaluated by dynamic thermogravimetry. The char yield was highest for resin cured with imide–amines NE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fourier transform infrared and 13C-NMR spectroscopic characterization of model epoxy networks

Model epoxy networks based on a diglycidylether of bisphenol A (DGEBA) or of butanediol (DGEBU) and cured with different mixtures of monoamines and diamines were prepared to allow changes in cross-link density. The choice of aliphatic or aromatic amines permitted assessment of the influence of network chain flexibility. Solid state ¹³C-NMR spectra showed that no secondary reactions leading to the creation of ether linkage occur during the condensation reaction. Glass transition temperatures (T_g) and the temperatures of the maximum of the exothermic cross-linking reaction (T_exo) were determined. A rectilinear increase of T_g as a function of the density of cross-links was observed for all the systems under study. Similarly, an increase in the stiffness of the backbone units resulted in an increase in T_g. Time-temperature-transformation (TTT) isothermal cure diagrams were constructed and infrared kinetics were performed at 90°C. Gelation and vitrification times were shown to be dependent on the nature of the amines used to create the network structure. © 1993 John Wiley & Sons, Inc.     

Curing and thermal behavior of epoxy resin in the presence of silicon‐containing amide amines

The article describes the synthesis and characterization of silicon‐containing amide amines obtained by the reaction of bis(4‐chlorobenzoyl)dimethylsilane with 4,4′‐diaminodiphenyl ether, 4,4′‐diaminodiphenyl methane, 4,4′‐diaminodiphenyl sulfone/3,3′‐diaminodiphenyl sulfone, bis(3‐aminophenyl)methyl phosphine oxide, and tris(3‐aminophenyl)phosphine oxide with dimethyl acetamide as a solvent. Structural characterization of amide amines was done with Fourier transform infrared and ¹H‐NMR spectroscopy. We used these aromatic amide amines as curing agents to investigate the effect of structure and molecular size on the curing and thermal behavior of diglycidyl ether of bisphenol A (DGEBA). The curing behavior of DGEBA in the presence of stoichiometric amounts of silicon‐containing aromatic amide amines was investigated by differential canning calorimetry. A broad exothermic transition in the temperature range of 200–300°C was observed in all the samples. The peak exotherm temperature was lowest in the case of phosphorus‐containing amides and was highest in the case of ether‐containing amides. Thermal stability of the isothermally cured resins was evaluated with dynamic thermogravimetry in a nitrogen atmosphere. A significant improvement in the char yield was observed with silicon‐containing amines, and it was highest in case of samples with both silicon and phosphorus as flame‐retarding elements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1345–1353, 2003     

Glass fiber‐reinforced composites of diglycidyl ether of 2,7‐dihydroxy naphthalene

The curing reactions of epoxy resin diglycidyl ether of 2,7‐dihydroxy naphthalene (DGEDHN) with different aliphatic and aromatic amines have been studied by differential scanning calorimetry (DSC). The thermal stability of the cured products was also studied by thermogravimetric analysis (TGA). Using these data, different glass fiber‐reinforced composites were fabricated, and their mechanical, electrical properties and resistance to chemicals were studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1345–1349, 2000     

Influence of chemical structure of hardener on mechanical and adhesive properties of epoxy polymers

The mechanical and adhesive properties of epoxy formulations based on diglycidyl ether of bisphenol A cured with various aliphatic amines were evaluated in the glass state. Impact and uniaxial compression tests were used to determine the impact energy, elastic modulus and yield stress, respectively. The adhesion tests were carried out in steel–steel joints using single‐lap shear, T‐peel, and impact adhesive joints geometry. The better mechanical and adhesive behavior of the networks is obtained when exists high flexibility of chain between crosslink and/or high elastic modulus. The 1‐(2‐aminoethyl)piperazine epoxy network presents the best adhesive properties, high flexibility, and the largest impact energy. However, it possesses low elastic modulus and yield stress. Also, exhibits increases in peel strength and impact energy while reductions in lap shear strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on curing kinetics and thermal behavior of phosphorylated epoxy resin in the presence of aromatic amide‐amines

This article describes the synthesis of some novel aromatic amide‐amine curing agents by reacting 1 mole of p‐amino benzoic acid with 1 mole of each of 1,4‐phenylene diamine (P), 1,5‐diamino naphthalene (N), 4,4′‐(9‐fluorenyllidene)‐dianiline (F), 3,4′‐oxydianiline (O), and 4,4′‐diaminodiphenyl sulphide (DS) and were designated as PA, NA, FA, OA, and SA, respectively. The aromatic amide‐amines so synthesized were characterized with the help of spectroscopic techniques, viz., Fourier Transform Infrared, proton nuclear magnetic resonance, and carbon nuclear magnetic resonance. The curing kinetics of the epoxy resins obtained by reacting amines with diglycidyl ether of bisphenol‐A blended with tris(glycidyloxy)phosphine oxide in a ratio of 3 : 2, respectively, were investigated by DSC technique using multiple heating rate method (5, 10, 15, 20°C/min). Activation energies were determined by fitting the experimental data into Kissinger and Flynn‐Wall‐Ozawa Kinetic models. The activation energies obtained through Flynn‐Wall‐Ozawa method were slightly higher than Kissinger method but were comparable. However, both the energies were found to be dependent on the structure of amines. The thermal stability and weight loss behavior of isothermally cured thermosets were also investigated using thermogravimetric analysis in nitrogen atmosphere. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects on Dielectric Properties of Modified Bismaleimide Resins

Abstract

Six modified bismaleimide (BMI) resin systems are developed. The modifier is diallyl bisphenol A, diallyl bisphenol A ether. TDE-85 epoxy/MNA anhydride, and styrene. respectively. In view of structure of those cured resins, relationships between structure and dielectric properties have been studied emphatically, while effects of postcure temperature and catalysts on dielectric properties were also shown. Results indicate that dielectric properties lie on structure of cured resin and postcure temperature; catalysts can strikingly improve the heat-resistance of materials, but has little effect on the dielectric properties. In addition, mechanical and thermal properties of neat resins were also shown.     

Structural heterogeneity in epoxies

The effects of different cure procedures on the structure and properties of epoxy samples made from diglycidyl ether of bisphenol A (DGEBA) and mixtures of two linear aliphatic diamines were studied. The elastic modulus, fracture toughness, impact resistance, and glass transition temperature were determined for various cure schemes. The morphologies of the cured resins were characterized with small angle X-ray scattering. The results show that samples with the same average morphology (molecular network structure) have similar elastic moduli and glass transition temperatures. If some heterogeneity is introduced in the molecular network structure without changing the average structure, however, the experiments indicate that the toughness can be increased without significantly sacrificing other properties.     

Processing–morphology–property relationships in epoxy resins

An investigation was conducted into processing–morphology–property relationships of a series of epoxy resin formulations. Diglycidyl ether of bisphenol A (DGEBA) epoxy resin was cured with diethylene triamine (DETA) and 2,5-dimethyl 2,5-hexane diamine (DMHDA). The two systems were compared by electron microscopic investigation and thermomechanical and fracture property measurements. Transmission electron microscopy has revealed a difference in the morphology of fracture surfaces. On the other hand, thermomechanical and fracture properties of DETA- and DMHDA-cured formulations were found to be very similar. Three different processing (curing) conditions were used for DMHDA-cured formulations, without an apparent effect on their properties. The previously reported improvement in impact energy of DMHDA-cured formulations is unfounded.     

Curing kinetics and properties of epoxy resin-fluorenyl diamine systems

Diglycidyl ether of bisphenol fluorene (DGEBF), 9,9-bis-(4-aminophenyl)-fluorene (BPF) and 9,9-bis-(3-methyl-4-aminophenyl)-fluorene (BMAPF) were synthesized to introduce more aromatic structures into the epoxy systems, and their chemical structures were characterized with FTIR, NMR and MS analyses. The curing kinetics of fluorenyl diamines with different epoxy resins including DGEBF, cycloaliphatic epoxy resin (TDE-85) and diglycidyl ether of bisphenol A (DGEBA) was investigated using non-isothermal differential scanning calorimetry (DSC), and determined by Kissinger, Ozawa and Crane methods. The thermal properties of obtained polymers were evaluated with dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results show that the values of activation energy (E_a) are strongly dependent on the structures of epoxy resin and curing agent. The curing reactivity of epoxy system is restrained by the introduction of rigid fluorene into chain backbone and flexible methyl into side groups. The cured DGEBF/fluorenyl diamine systems exhibit remarkably higher glass transition temperature, better thermal stability and lower moisture absorption compared to those of DGEBA/fluorenyl diamine systems, and display approximate heat resistance and much better moisture resistance relative to those of TDE-85/fluorenyl diamine systems.     

糠醇缩水甘油醚稀释的环氧体系的性能研究

通过力学性能和热性能测试研究了糠醇缩水甘油醚(FGE)稀释的双酚A环氧树脂(DGEBA)体系的固化性能和固化反应动力学。通过Málek自催化机理模型求得添加10%FGE的DGEBA与脂肪族聚酰胺固化剂的固化反应平均活化能为64.66kJ/mol,低于苄基缩水甘油醚(BGE)稀释体系。以FGE稀释的固化产物的拉伸强度达到62.93MPa,比BGE体系高出20%左右。拉伸伸长率达4.66%,是BGE体系的4倍左右。添加FGE的固化物冲击强度达36.17MPa,比BGE体系高出约70%左右。使用FGE和BGE的环氧固化物的玻璃化转变温度分别为46.32℃和52.36℃。FGE和BGE体系固化物的5%的热失重温度分别为260.79℃和194.59℃。FGE是1种良好的环氧树脂稀释剂。