Tertiary‐amine‐free,non‐planar,sulfone‐containing,tetrafunctional epoxy and its application as a high temperature matrix

Non‐amine‐derived tetrafunctional epoxies have several advantages over the amine‐derived N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenyl methane (TGDDM) in high temperature applications. Although two non‐amine‐derived tetrafunctional epoxies were developed in our laboratory, further improvements in toughness using less loading amount is still desirable. Thus, a tertiary‐amine‐free, non‐planar and triphenylmethane‐containing tetrafunctional epoxy (STFE) with a sulfone spacer was synthesized. When it was mixed with diglycidyl ether of bisphenol A (DGEBA) and cured with 4,4′‐diaminodiphenylsulfone (DDS), both thermal and mechanical performances outperformed TGDDM. Moreover, STFE modified system shows the highest toughness (35.7 kJ m^–2) among three amine‐free and triphenylmethane‐containing epoxies at merely 5 wt% loading. Molecular simulation and thermomechanical analysis results suggest that the improved mechanical properties could be related to the geometry of the molecule and larger free volume. Despite a marginal drop in T_g, the thermal degradation temperature is better than that of TGDDM/DDS. In addition, the moisture resistance of STFE/DGEBA/DDS is much better than that of TGDDM/DDS. Thus, STFE modified DGEBA could be a potential replacement for TGDDM in some high temperature applications. © 2020 Society of Chemical Industry     

Fibre reinforced composites of multifunctional epoxy resins

Glass and carbon fibre reinforced epoxy composites were fabricated for N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and its formulated systems with tri- and di-functional reactive epoxy diluents using 30% diaminodiphenyl sulphone (DDS) as a curing agent. The epoxy laminates were evaluated for their physical, chemical and mechanical properties [at room (26°C) and high (100°C) temperatures]. A marginal increase (<20%) in the mechanical properties of CFRP was found compared with GFRP laminates. Incorporation of epoxy diluents altered the mechanical properties of the composites significantly. The incorporation of triglycidyl-4-aminophenol diluent to TGDDM systems resulted in an improvement in mechanical properties of about 2–6%.     

Cure kinetics of multifunctional epoxies with 2,2′‐dichloro‐4,4′‐diaminodiphenylmethane as hardener

The curing behavior of the epoxy resin N,N,N′,N′‐tetraglycidyldiaminodiphenyl methane (TGDDM) with triglycidyl p‐aminophenol as a reactive diluent was investigated using 2,2′‐dichloro‐4,4′‐diaminodiphenylmethane (DCDDM) as the curing agent. The effect of the curing agent on the kinetics of curing, shelf‐life, and thermal stability in comparison with a TGDDM‐diaminodiphenylsulfone (DDS) system was studied. The results showed a lesser activation energy at the lower level of conversion with a broader cure exotherm for the epoxy‐DCDDM system in comparison with the epoxy‐DDS system, although the overall activation energy for the two systems was comparable. TGA studies showed more stability in the epoxy‐DCDDM system than in the epoxy‐DDS system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2097–2103, 2000     

Imidazole and chromium acetylacetonate as additives for the cure and fracture toughness of epoxy resins and their composites

The effects of additives such as 2-undecyl-imidazole (C₁₁Z) and chromium acetylacetonate (Cr(acac)₃) were examined on the curing behavior and fracture toughness of tetraglycidyldiaminodiphenyl methane/diaminodiphenyl sulphone (TGDDM/DDS) epoxy resins and their composites. The C₁₁Z additive alone reacted with TGDDM epoxy resins at about 127°C and increased the resin viscosity, resulting in an acceptable resin content for composite processing. Further addition of Cr(acac)₃ to TGDDM/DDS/C₁₁Z formulation increased the fracture toughness 5.7 times compared to the typical TGDDM/DDS/BF₃MEA epoxy formulation used for the preparation of laminates. The interlaminar fracture toughness of the laminates prepared by TGDDM/DDS/C₁₁Z/Cr(acac)₃ formulation was only twice as much as that prepared by typical TGDDM/DDS/BF₃MEA. This was due to the fiber bridging contribution to the interlaminar fracture toughness. Based on the experiment, this fiber bridging contribution was only dependent on the fiber content. Thus, the interlaminar fracture toughness is approximated by the sum of the fracture toughness of epoxy matrix and the estimated fiber bridging contribution.     

Morphologies and mechanical properties of polyethersulfone modified epoxy blends through multifunctional epoxy composition

Thermoplastic polyethersulfone (PES) modified multifunctional tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) and triglycidyl para‐aminophenol (TGAP) epoxy prepolymers cured with 4,4′‐diaminodiphenylsulfone (44DDS) were prepared using a continuous reactor method and their reaction‐induced phase separated morphologies and mechanical properties were measured and correlated with chemical compositions. ¹H nuclear magnetic resonance (¹H NMR) and near‐infrared spectroscopy (NIR) were used to quantify the chemical network formation. Atomic force microscopy (AFM) with nanomechanical mapping was employed to resolve the nanoscale phase‐separated morphologies. The extent of phase separation in cured networks and resultant domain sizes were determined to be controllable depending upon the multifunctional epoxy compositions. The results obtained from mechanical studies further indicated that tensile modulus was not largely affected by multifunctional epoxy compositions while fracture toughness increased with increase of TGAP content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44775.     

Synthesis,characterization, and properties of low viscosity tetra‐functional epoxy resin N,N,N′,N′‐ tetraglycidyl‐3,3′‐diethyl‐4,4′‐diaminodiphenylmethane

Tetra‐functional epoxy resin N,N,N′,N′‐tetraglycidyl‐3,3′‐diethyl‐4,4′‐diaminodiphenylmethane (TGDEDDM) was synthesized and characterized. The viscosity of TGDEDDM at 25°C was 7.2 Pa·s, much lower than that of N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM). DSC analysis revealed that the reactivity of TGDEDDM with curing agent 4,4′‐diamino diphenylsulfone (DDS) was significantly lower than that of TGDDM. Owing to its lower viscosity and reactivity, TGDEDDM/DDS exhibited a much wider processing temperature window compared to TGDDM/DDS. Trifluoroborane ethylamine complex (BF₃‐MEA) was used to promote the curing of TGDEDDM/DDS to achieve a full cure, and the thermal and mechanical properties of the cured TGDEDDM were investigated and compared with those of the cured TGDDM. It transpired that, due to the introduction of ethyl groups, the heat resistance and flexural strength were reduced, while the modulus was enhanced. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40009.     

Low moisture absorptive epoxy formulations for Gr/Ep laminates

The incorporation of 2-undecyl-imidazole (C₁₁Z) and chromium acetylacetonate (Cr(acac)₃) additives into N, N, N′, N′-tetraglycidyl diaminodiphenylmethane (TGDDM)/diaminodiphenylsulfone (DDS) epoxy formulations was found to significantly decrease the moisture absorption of their prepared graphite/epoxy laminates. However, the same additions did not much affect the moisture absorption of the cured TGDDM/DDS neat resins. Thus, the former case was attributed to the processing effects in view of the fact that C₁₁Z pre-reacting with TGDDM during lay-up process produced the ether-linkage polymer chains in the epoxy networks and raised the viscosity. The following compacting stage of laminates was believed to squeeze the small molecules such as unreacted TGDDM, DDS and Cr(acac)₃, toward the surface of carbon fibers and increase the chance of Cr(acac)₃ to block the hydroxyl groups in the epoxy networks produced by the reactions between TGDDM and DDS. Some evidence was provided to support the above hypothesis in this study.     

Synthesis, curing behavior and properties of siloxane and imide-containing tetrafunctional epoxy

A novel tetrafunctional epoxy resin containing siloxane and imide groups, i.e., N,N,N′,N′-tetraglycidyl-bis(4-aminophenyl)-5,5′ (1,1,3,3-tetramethyl-1,1,3,3-disiloxane-bisnorbornane-2,3-dicaroximide, was synthesized and characterized. The curing behavior of this resin and the properties of its cocured material with commercial tetraglycidyl meta-xylene (GA-240) was studied. Functional group changes during cocuring reactions were investigated with FTIR. Kinetic parameters were analyzed with dynamic DSC. Thermal properties were measured with TGA, TMA and DMA. Curing kinetics revealed that this novel tetrafuctinal epoxy indicated a lower activation energy and lower curing temperature than GA-240. The cocured materials, due to the presence of siloxane and imide groups in the polymer matrix, show higher glass transition temperature, better dimensional stability and toughness, and also enhanced properties than pure GA-240.     

Structure characterization,reactivity, and thermal properties of new cyclic phosphine oxide epoxy resin containing tetra-oxirane rings

A new type of epoxy resin, which contained cyclic phosphine oxide and tetra-oxirane rings in the main chain, was synthesized. The structure of the new type of epoxy resin was confirmed by elemental analyses (EA), infrared (IR) spectroscopy, and ¹H nuclear magnetic resonance (NMR) and ¹³C-NMR spectroscopies. In addition, compositions of the new synthesized cyclic phosphine oxide epoxy resin (TGCAO) with three curing agents, for example, bis(3-aminophenyl)ethylphosphine oxide (BEMP), 4,4′-diaminodiphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS) were used for making a comparison of its curing reactivity, heat, and flame retardancy with those of Epon 828 and DEN438. The reactivities were measured by differential scanning calorimetry. Through the evaluation of thermal gravimetric analysis, those polymers, which were obtained through the curing reactions between the new epoxy resin and three curing agents (BEMP, DDM, and DDS), also demonstrated adequate thermal propeties, as well as a high char yield. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1397–1409, 1998     

A study on the effect of new cyanate and phenoxy polymer on TGDDM/DDS/GMP formulations

An attempt was made on the modification of the tetraglycidyl‐4,4′‐diaminodiphenyl methane/diaminodiphenyl sulfone (TGDDM/DDS) system to improve properties for several industrial applications. Epoxy resins [TGDDM and 1‐glycidyloxy‐4‐methoxy phenol (GMP)] were synthesized in the laboratory. Also, a new cyanate ester and phenoxy polymer were synthesized and characterized by FTIR, ¹H‐/¹³C‐NMR, and thermal studies. GMP was added as a diluent and a new cyanate ester (DCDPT) was introduced to reduce the tight crosslinking density. Further, a new phenoxy polymer was added to improve the toughness property. A variety of neat resin casts using different compositions of the blends were made and their physical, chemical, thermal, and mechanical properties were evaluated to study the effect of GMP as a diluent, cyanate ester as a comonomer, and phenoxy polymer as a toughener. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2963–2973, 2003     

Effects of Fortifier on Glass/Carbon Fiber Reinforced Tetrafunotional Epoxy Resin

Glass fiber reinforced epoxy composites were prepared using tetra-N-glycidyl-p,p′-diaminodiphenyl methane (TGDDM) as a resin matrix with/without fortifier PGEHA/VCDRC (at 20 phr level) using DDM/DDS as curing agent; the composites were evaluated for their various physical, mechanical, chemical, and electrical properties. Carbon fiber (i.e., unidirectional, bidirectional, and chopped) reinforced composites of TGDDM with/without epoxy fortifier PGEHA/VCDRC (at 20 phr level) were also prepared and evaluated for their physical and some mechanical and chemical properties. It is observed that incorporation of fortifier (at 20 phr level) improves these properties significantly.     

Toughening of epoxy resins with thermoplastics. Ii. Tetrafunctional epoxy resin-polyetherimide blends

A series of blends has been prepared by adding a polyetherimide (PEI), in varying proportions, to a tetrafunctional epoxy resin, tetraglycidyl-diaminodiphenylmethane (TGDDM), cured with 4,4′-diaminodiphenylsulphone (DDS). All the materials exhibited two-phase morphologies which were characterised by dynamic mechanical thermal analysis and scanning electron microscopy. Addition of the thermoplastic gave a modest improvement in fracture properties (K_1c and G_1c), as determined by three-point bending experiments, although no obvious correlation with the marked morphological changes was observed.     

Fluid uptake behavior of multifunctional epoxy blends

Profound changes in network architecture from blending trifunctional (m-triglycidylaminophenol, mTGAP) or tetrafunctional (tetraglycidyldiaminodiphenylmethane, TGDDM) epoxides with diglycidyl ether of bisphenol-A (DGEBA) and a curative amine (3,3′-diaminodiphenylsulfone, 3,3′-DDS) were observed using PVT, DMA, and PALS analyses. Increasing multifunctional content, which increased the crosslink density (with the expected increase in T_g), produced a decrease in the average free volume hole size (V_h) accompanied by a counterintuitive increase in fractional free volume (FFV). This unusual inverse relationship between FFV and V_h allowed clear resolution of their respective roles in equilibrium moisture uptake vs. the rate of uptake (diffusivity). Equilibrium water uptake increased with increasing multifunctional content, concomitant with the increase in FFV. Water diffusivity, on the other hand, decreased with increasing multifunctional content, concomitant with the decrease in V_h. The decreasing V_h in the epoxy blends also had interesting consequences for organic solvent sensitivity. MEK ingress was substantial in the binary DGEBA/DDS epoxy and completely inhibited for most of the blends, implying hole size selectivity was responsible for the MEK uptake inhibition. MEK uptake was precluded in epoxies whose V_h was below a critical threshold value of ～68 Å³. A small amount of mTGAP or TGDDM was sufficient to reduce the V_h of DGEBA/DDS epoxy below the threshold and prevent MEK uptake.     

Cure monitoring of aerospace epoxy resins and prepregs by Fourier transform infrared emission spectroscopy

Spectral analysis of the infrared radiation emitted from thin films of resin transferred from the surface of high performance aerospace carbon fibreepoxy composite prepregs and heated to the cure temperature allows the cure chemistry and kinetics to be monitored in real time. Quantitative spectra with excellent signal-to-noise ratio are obtained by heating a thin resin film on a platinum hotplate fitted to the external optics of a Fourier transform infrared (FTIR) spectrometer and referencing the resulting emission (with the platinum emission subtracted) to a graphite black body at the same temperature. The resulting spectra are identical to absorption spectra and the quantitative features of the analysis are demonstrated by the appearance of isosbestic points during the curing reactions, so indicating that concentration profiles of the reacting species may be obtained. From the initial rate of amine and epoxy consumption, activation energies of 75kJ mol⁻¹ were obtained for both functional groups in the uncatalysed resin 4,4′-tetraglycidyl diamino diphenyl methane (TGDDM) with 27% 4,4′-diaminodiphenylsulfone (DDS), while values of 74 and 89kJ mol⁻¹ were obtained for amine and epoxy consumption from the TGDDM/DDS prepreg catalysed with boron trifluoride monoethylamine (Hercules 3501–6), consistent with homopolymerization occurring in the prepreg as well as amine–epoxy addition. Analysis of the FTIR emission at 177°C of resin from prepreg aged up to 90h at 23°C and 55% relative humidity shows a lowering of epoxy and amine concentration and a higher rate of cure, consistent with the formation of catalytic species. This technique may be used to monitor changes in surface properties such as tack and resin transfer, in addition to changes in the cure profile of the aged epoxy propreg.     

The synthesis and properties of new epoxy resin containing phosphorus and nitrogen groups for flame retardancy

A new type of epoxy resin, which contained phosphorus oxide and nitrogen groups in the main chain, was synthesized. The structure of the new type of epoxy resin was confirmed by infrared (IR) spectroscopy, ¹H nuclear magnetic resonance (¹H‐NMR), and ¹³C‐NMR spectroscopic techniques. In addition, compositions of the new synthesized epoxy resin (TGDMO) with three curing agents, for example, bis(3‐aminophenyl) methylphosphine oxide (BAMP), 4,4′‐diaminodiphenylmethane (DDM), and 4,4′‐diaminodiphenylsulfone (DDS), were used for making a comparison of its curing reactivity, heat, and flame retardancy with that of Epon 828 and DEN 438. The reactivities were measured by differential scanning calorimetry (DSC). Through the evaluation of thermal gravimetric analysis (TGA), those polymers which were obtained through the curing reactions between the new epoxy resin and three curing agents (BAMP, DDM, and DDS) also demonstrated excellent thermal properties as well as a high char yield. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 413–421, 1999     

Isothermal curing by dynamic mechanical analysis of three epoxy resin systems: Gelation and vitrification

Times to gelation (t_gel) and times to vitrification (t_vit) during isothermal curing for the epoxy systems diglycidyl ether of bisphenol A (DGEBA)/1,3‐bisaminomethylcyclohexane (1,3‐BAC), tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM)/4‐4′‐diaminodiphenylsulfone (DDS), and TGDDM/epoxy novolac (EPN)/DDS were measured at different curing temperatures. This article reports on a method to determine t_gel and t_vit by dynamic mechanical analysis (DMA). Gelation was determined at the onset of the storage modulus or by the peak of the loss factor. Vitrification was defined as the curve of the storage modulus as the curve reached a constant level (endset) in DMA tests. The experimental values obtained for t_gel and t_vit were compared with values obtained by other experimental methods and with theoretical values (t_gel's) or indirect determinations (t_vit's). From kinetic analysis by differential scanning calorimetry, conversions corresponding to gelation were obtained for the three systems; this yielded a constant value for each system that was higher than theoretical value. Values of the apparent activation energies of the DGEBA/1,3‐BAC, TGDDM/DDS, and TGDDM/EPN/DDS epoxy systems were obtained from plots of t_gel's against reciprocal temperatures. They were 53.2, 58.2, and 46.5 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 78–85, 2002     

Novel adamantane‐containing epoxy resin

A novel adamantane‐containing epoxy resin diglycidyl ether of bisphenol‐adamantane (DGEBAda) was successfully synthesized from 1,3‐bis(4‐hydroxyphenyl)adamantane by a one‐step method. The proposed structure of the epoxy resin was confirmed with Fourier transform infrared, ¹H‐NMR, gel permeation chromatography, and epoxy equivalent weight titration. The synthesized adamantane‐containing epoxy resin was cured with 4,4′‐diaminodiphenyl sulfone (DDS) and dicyandiamide (DICY). The thermal properties of the DDS‐cured epoxy were investigated with differential scanning calorimetry and thermogravimetric analysis (TGA). The dielectric properties of the DICY‐cured epoxy were determined from its dielectric spectrum. The obtained results were compared with those of commercially available diglycidyl ether of bisphenol A (DGEBA), a tetramethyl biphenol (TMBP)/epoxy system, and some other associated epoxy resins. According to the measured values, the glass‐transition temperature of the DGEBAda/DDS system (223°C) was higher than that of the DGEBA/DDS system and close to that of the TMBP/DDS system. TGA results showed that the DGEBAda/DDS system had a higher char yield (25.02%) and integral procedure decomposition temperature (850.7°C); however, the 5 wt % degradation temperature was lower than that of DDS‐cured DGEBA and TMBP. Moreover, DGEBAda/DDS had reduced moisture absorption and lower dielectric properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis, characterization, thermal and flame retardant properties of novel aryl phosphinate diglycidyl ether cured with anhydride

A novel aryl phosphinate diglycidyl ether, 10-(2′,5′-diglycidyl ether phenyl)-9,10-dihydro-9-oxa-l0-phosphaphenanthrene-10-oxide (DHQEP), was synthesized. The structure of the diglycidyl ether was characterized by elemental analysis, mass, FTIR, ¹H, ¹³C, ³¹P NMR spectroscopies and X-ray single crystal analysis. In addition, compositions of the diglycidyl ether with three curing agents, e.g. phthalic anhydride (PA), hexahydrophthalic anhydride (HHPA), and aryl phosphinate anhydride (DMSA), were used for making a comparison of its heat and flame retardancy with that of DER331 and DEN438. The resulting aryl phosphinate epoxy-resin composites demonstrated a higher limiting oxygen index (LOT) value as well as a higher char yield, confirming the effectiveness of aryl phosphinate epoxide as a flame retardant for epoxy resins.     

Alkoxysilane oligomer modified epoxide primers

Telechelic resins with reactive end groups (epoxy phosphate and epoxy ester) were synthesized using bisphenol-A (BPA) epoxide. The bisphenol-A based epoxide, the epoxy phosphate, and the epoxy ester were all modified with tetraethylorthosilicate (TEOS) oligomers, which were prepared through the hydrolysis and condensation of TEOS monomer with water under acidic condition. The epoxide/polysilicate (organic/inorganic) hybrid systems were characterized systematically, using FTIR, ¹H, ¹³C, ³¹P, and ²⁹Si NMR, and MALDI-TOF. The modified epoxides were thermally cured with a melamine-formaldehyde resin, cast on steel substrates. The coating performance of the modified epoxides was evaluated by pencil hardness, crosshatch adhesion, reverse and direct impact resistance, mandrel bending, and pull-off adhesion. Viscoelastic properties of the hybrid systems were also evaluated as a function of polysilicate content. Corrosion performance was evaluated via salt spray (fog) test for 264 h. Salt spray analysis revealed that inorganically modified epoxides provided improvement over the unmodified epoxide resins with respect to both corrosion resistance and adhesion to steel substrates.     

Epoxy resin cure. II. FTIR analysis

Fourier transform infrared (FTIR) spectroscopy is used to determine the cure rate of an epoxy resin consisting of Tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and diaminodiphenylsulfone (DDS). Cure rates at 120 and 160°C are shown to increase noticeably when 1% BF₃–MEA is added to either TGDDM to TGDDM plus DDS. Fluoroboric acid is shown to increase the cure rates even more than the BF₃–MEA. These Results combined with the NMR results in the accompanying article indicate that BF₃–MEA is not a catalyst for epoxy resin cure. Instead it is rapidly hydrolyzed to fluoroboric acid which acts as the catalyst.