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     

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     

Cure kinetic study of carbon nanofibers/epoxy composites by isothermal DSC

An investigation was carried out into the cure kinetics of carbon nanofibers (CNF)/epoxy composites, composed of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) resin and 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent. The experimental data for both neat system and CNF/epoxy composites revealed an autocatalytic behavior. Analysis of DSC data indicated that the presence of carbon nanofibers had only a negligible effect on the cure kinetics of the epoxy. Kinetic analysis was performed using the phenomenological model of Kamal and two diffusion factors were introduced to describe the cure reaction in the latter stage. Activation energies and kinetic parameters were determined by fitting experimental data. Comparison between the two diffusion factors was performed, showing that the modified factor was successfully applied to the experimental data over the whole curing temperature range. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 329–335, 2005     

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     

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.     

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.     

Thermal characterization of carbon‐nanofiber‐reinforced tetraglycidyl‐4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone epoxy composites

The thermal properties of carbon nanofibers (CNF)/epoxy composites, composed of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) resin and 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent, were investigated with differential scanning calorimetry (DSC), thermogravimetric analysis, and dynamic mechanical thermal analysis. DSC results showed that the presence of CNF had no pronounced influence on the heat of the cure reaction. However, the incorporation of CNF slightly improved the thermal stability of the epoxy. Furthermore, the storage modulus of the TGDDM/DDS epoxy was significantly enhanced, whereas the glass‐transition temperature was not significantly affected, upon the incorporation of CNFs. The storage modulus of 5 wt % CNF/epoxy composites at 25°C was increased by 35% in comparison with that of the pure epoxy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 295–298, 2006     

Curing,compatibility, and fracture toughness for blends of bismaleimide and a tetrafunctional epoxy resin

The curing, compatibility, and fracture toughness of blends of 4,4 ′-bismaleimidodiphenylmethane (BDM)/tetraglycidyl diamino-diphenyl methane (TGDDM) were investigated. Diamino-diphenyl sulfone (DDS) was used as a curing agent. BDM alone could be both homopolymerized (at a lower temperature) and could also undergo Michael addition reactions with the primary amine of DDS. The secondary amine of DDS did not react with BDM. However, the network produced by homopolymerization was not miscible with that produced by the latter reactions. Curing of TGDDM with DDS took place almost at the same temperature as that of the homopolymerization of BDM, but well below the temperature of the Michael addition reaction. When a BDM/TGDDM mixture was cured with DDS in the stoichiometric ratio, the miscibility of the cured system increased with the amount of TGDDM. This was attributed to the fact that the network produced by Michael addition reactions was diminished. When DDS reacted entirely with TGDDM, the BDM/TGDDM/DDS cure yielded only a TGDDM/DDS network and a BDM homopolymerized network, which were not only miscible, but are also interpenetrating. The superior interpenetrated network, as indicated by the highest fracture toughness, was found at BDM/TGDDM = 40/60 weight ratio in the BDM/TGDDM/DDS curing systems.     

Thermal and microwave‐assisted oxidative degradation of poly(ethylene oxide)

The kinetics of the thermal and microwave‐assisted oxidative degradation of poly(ethylene oxide) were determined with potassium persulfate as the oxidizing agent. Gel permeation chromatography was used to determine the variation of the molecular weight with time. The degradation was studied as a function of the temperature and persulfate concentration, and it was found that the degradation rate increased with the temperature and concentration of persulfate. Continuous distribution kinetics were used to determine the rate coefficients for the degradation process, and the activation energies were obtained. The results indicated that the microwave‐assisted process had a lower activation energy of 10.3 kcal/mol, whereas that of the thermal degradation was 25.2 kcal/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2090–2096, 2005     

Thermokinetics and chemorheology of the cure reactions of the tetraglycidyl diamino diphenyl methane–diamino diphenyl sulfone epoxy systems

The cure behavior of commercial grade TGDDM–DDS mixtures of compositions ranging from 10 to 100 phr of hardener and the thermal polymerization of the epoxy component are analyzed by means of differential scanning calorimetry. The kinetic parameters and heats of reaction determined in isothermal and dynamic scans suggest that DDS primary amine addition and epoxide etherification dominate the cure reactions. The primary amine epoxide addition is characterized by overall heat of reaction (referred to the weight of the epoxy component) of 255 cal/g and by an activation energy of 16.6 kcal/mol. The corresponding values for the etherification reaction are, respectively, 170 cal/g and 41 kcal/mol. A method of derivation of the epoxide conversion from the heat evolved in DSC thermal scans of these systems is presented. The results are in good agreement with independent IR determinations. The steady shear and oscillatory viscosity measurements and the calorimetric analysis of the isothermal cure at 140°C, 160°C, and 180°C of a TGDDM–DDS mixture containing 35 phr of hardener indicate that gelation is principally governed by the primary amine addition. The gelation limits calculated in isothermal tests by combining the calorimetric analysis and the theory describing the nonlinear copolymerization of the tetrafunctional TGDDM with an essentially difunctional DDS were in good agreement with the values experimentally determined through rheological measurements.     

Evaluating the thermal stability of high performance fibers by TGA

The thermal degradation of eight types of high performance fibers (HPFs) was measured under nitrogen and air atmosphere. The degree of degradation, as measured by weight loss using thermogravimetric analysis (TGA), and the characteristic degradation temperatures were obtained. The kinetics of the thermal degradation has also been analyzed according to the Freeman–carroll method and the activation energies of the HPFs were estimated. The experimental results show that para‐aramids (Kevlar® 29, 49, 129, and Twaron®2000) have similar thermal stability, but their thermal degradation temperatures and activation energies in air are different from those in nitrogen, which means that the thermostability of the fiber depends not only on its intrinsic structure but also on the atmosphere and temperature of testing environment. Terlon® fiber shows higher degradation temperature as a copolymer of para‐aramid, and its initial degradation temperature is 476.4°C in air. It can also be found that the PBO (poly(p‐phenylene benzobisoxazole)) fiber has the highest thermal degradation temperature among the samples tested, but its activation energy is not the highest in both air and nitrogen atmosphere. And the UHMW‐PE (ultra high molecular weight polyethylene) fiber has the lowest thermal degradation temperature, and it begins to degrade when the temperature reaches 321.8°C under air atmosphere. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 937–944, 2006     

Thermal degradation kinetics of polyesters containing mesogenic aromatic diols

A series of polyesters were synthesized by reacting structurally differing aromatic diols with either saturated (flexible) or unsaturated (rigid) dicarboxylic acid halide by a stirred interfacial polycondensation technique. Thermal degradation kinetics of these polyesters were investigated by applying Coats–Redfern and Horowitz–Metzger nonisothermal procedures. The dynamic thermogravimetry experiments were conducted in nitrogen to obtain differential thermogravimetric plots. Thermal stability of these polyesters was discussed on the basis of semiquantitative methods such as differential procedural decomposition temperature, integral procedural decomposition temperature, and fraction decomposition temperature (e.g., 10% DT). Degradation proceeded in multiple stages. The thermal degradation patterns and activation energies in these stages were discussed in relation to central bridging moieties of aromatic diol. The activation energies of these polyesters were found to be in the range of 100 to 200 kJ/mol. The effect of spacer type on activation energy was also reported. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 784–792, 2005     

Cure kinetics of neat and graphite-fiber-reinforced epoxy formulations

An investigation was carried out into the cure kinetics of neat and graphite fiber-reinforced epoxy formulation, composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) resin and diaminodiphenyl sulfone (DDS) curing agent. Two experimental techniques were employed: isothermal differential scanning calorimetry (IDSC) and dynamic differential scanning calorimetry (DDSC). An autocatalytic mechanism with the overall reaction rate order of 2 was found to describe adequately the cure kinetics, of the neat resin and the composite. All kinetic parameters, including reaction rate constants, activation energies and preexponential factors, were calculated and reported. The presence of graphite fibers in the composite had only a very small initial effect on the kinetics of cure.     

Dielectric studies of the cure of epoxy matrix systems

Dielectric spectroscopy was used to monitor the curing process of two epoxy resin systems. The basic system (system I) consisted of DGEBA (a difunctional epoxy) and a polyamide in a 50–phr mixture. In addition, a comparative analysis was performed on a high–performance resin system (system II) used primarily in unidirectional composite applications. This system contained TGDDM (a tetrafunctional epoxy) and DDS (a tetrafunctional amine) in a 25–phr mixture. The dielectric data were obtained using a simple yet functional sample cell electrode designed and constructed in the laboratory. For system I, isothermal dielectric data were used to determine apparent activation energies for the temperature range from 22 to 70°C. The data showed that the activation energy was a function of temperature and increased as the temperature of the cure increased. This indicated that the reaction mechanism was also a function of temperature. For system II, data were collected between 140 and 190°C and an overall activation energy for that temperature range was determined. The overall activation energies for both systems, calculated using dielectric spectroscopy, compared favorably to those obtained using differential scanning calorimetry. Also, using a wider frequency range (240 Hz to 2 MHz), Argand diagrams were constructed and modeled with the Cole–Cole empirical equation for systems with a distribution of relaxation times. This justified the calculation of average relaxation times, which could then be related to the bulk physical properties of the polymer, such as viscosity. Modified Argand diagrams, where ε″ is plotted against ε′ at one frequency as a function of time, were also constructed, which aided in the understanding of the curing processes for these thermosetting systems.     

Effect of zeolite filler on the thermal degradation kinetics of polypropylene

In this study, the thermal degradation behavior of polypropylene (PP) and PP–zeolite composites was investigated. Clinoptilolite, a natural zeolitic tuff, was used as the filler material in composites. The effects of both pure clinoptilolite and silver‐ion‐exchanged clinoptilolite on the thermal degradation kinetics of the PP composites was studied with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Polymer degradation was evaluated with DSC at heating rates of 5, 10, and 20°C/min from room temperature to 500°C. The silver concentration (4.36, 27.85, and 183.8 mg of Ag/g of zeolite) was the selected parameter under consideration. From the DSC curves, we observed that the heat of degradation values of the composites containing 2–6% silver‐exchanged zeolite (321–390 kJ/kg) were larger than that of the pure PP (258 kJ/kg). From the DSC results, we confirmed that the PP–zeolite composites can be used at higher temperatures than the pure PP polymer because of its higher thermal stability. The thermal decomposition activation energies of the composites were calculated with both the Kissinger and Ozawa models. The values predicted from these two equations were in close agreement. From the TGA curves, we found that zeolite addition into the PP matrix slowed the decomposition reaction; however, silver‐exchanged zeolite addition into the matrix accelerated the reaction. The higher the silver concentration was, the lower were the thermal decomposition activation energies we obtained. As a result, PP was much more susceptible to thermal decomposition in the presence of silver‐exchanged zeolite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 143–148, 2006     

Studies on the curing kinetics and thermal stability of diglycidyl ether of bisphenol‐A using mixture of novel,environment friendly sulphur containing amino acids and 4,4′‐diaminodiphenylsulfone

This article describes the curing behavior of diglycidyl ether of bisphenol‐A using Cysteine (A)/ Methionine (B)/Cystine (C)/ mixture of 4,4′‐diaminodiphenyl sulfone (DDS) and Cysteine/DDS and Methionine/DDS and Cystine in various molar ratios as curing agent. Differential scanning calorimetry was used to study the cure kinetics by recording the DSC scans at heating rates of 5, 10, 15, and 20°C/min. The peak exotherm temperature was found to be dependent on the heating rate, structure of the amino acids and on the DDS/amino acids molar ratio. A broad exotherm was observed in the temperature range of 150–245°C (EA), 155–240°C (EB), and 190–250°C (EC). Curing of DGEBA with mixture of amino acids and 4, 4′‐diaminodiphenyl sulfone (DDS) resulted in a decrease in characteristic curing temperatures. Activation energy of curing reaction is determined in accordance to Ozawa's method and was found to be dependent on the structure of the amino acids and on the ratio of 4,4′‐diaminodiphenyl sulfone (DDS) to amino acid. Thermal stability of the isothermally cured resins was evaluated using dynamic thermogravimetry in nitrogen atmosphere. No significant change has been observed in the char yield of all the samples, but it was highest in the system cured using either Cystine alone (EC‐1) or a mixture of DDS/Cystine (EC‐2, EC‐3, and EC‐4). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

An investigation of cure and thermal stability of poly(amide‐amidic acid) modified tetraglycidyl 4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone

In this work, poly(amide‐amidic acid) (PAA) was used to modify tetraglycidyl 4,4′‐diaminodiphenylmethane (TGDDM)/4,4′‐diaminodiphenylsulfone (DDS) system. Results of non‐isothermal differential scanning calorimetry analysis indicated that PAA played a role of catalyst during the process of the curing reaction. The curing mechanism was studied by Fourier transform infrared spectroscopy, showing that the PAA acted as a co‐curing agent in the system. The glass transition temperature decreased firstly and then increased with the increase of the PAA content. PAA equally rendered TGDDM more fire resistant with higher char yield. On examining the fracture surface morphology using scanning electron microscopy, it was observed that there was no obvious phase separation when the content of PAA was less than 20 phr (per hundred weight of TGDDM/DDS resin), however, phase separation was observed when the content of PAA was 25 and 30 phr. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Studies on the thermal stability and degradation kinetics of Pd/PC nanocomposites

Effect of heating rate, Pd content, and synthesis method on the thermal stability of the ex situ and in situ Palladium/polycarbonate (Pd/PC) nanocomposites was investigated. TEM images revealed discrete Pd nanoclusters of about 5 and 15 nm sizes for 1 and 2 vol % ex situ nanocomposites, respectively. However, agglomerated Pd nanoclusters were noticed in the in situ samples, irrespective of the Pd content. The ex situ Pd/PC nanocomposites showed high onset temperature (Ti) for thermal degradation of PC than the in situ and pure PC samples. Pd content and heating rates were found to have a positive influence on the Ti and Tm (temperature at the maximum degradation rate occurs) of the Pd/PC nanocomposites. Thermal degradation of the PC was found to follow the first‐order kinetics in the Pd/PC nanocomposites. The activation energies associated with the degradation were determined by using the Kissinger method. These activation energies are used to construct the Master decomposition curve (MDC) and weight–time–temperature (α–t–T) plots that describe the time‐temperature dependence of the PC pyrolysis in the Pd/PC nanocomposites. These constructed α–t–T plots were validated with the data from isothermal measurements. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Kinetics of Curing and Thermal Degradation of POSS Epoxy Resin/DDS System

Polyhedral oligomeric silsesquioxanes epoxy resin (POSSER) was prepared from 3-glycidypropyl-trimethoxysilane (GTMS) and tetramethylammonium hydroxide (TMAH) by hydrolytic condensation. POSSER was characterized using Fourier-transformed infrared spectroscopy (FTIR), ¹H-NMR, and liquid chromagraphy/mass spectrometry (LC/MS). The epoxy value of POSSER is 0.50 mol/100 g. The LC/MS analysis indicated that T₁₀ is the majority and contain some amount of T₈, besides, a trace T₉ also exists. The curing kinetics of POSSER with 4,4′-diaminodipheny sulfone (DDS) as a curing agent was investigated by means of differential scanning calorimetry (DSC). The curing reaction order n is 0.8841 and the activation energy Ea is 61.06 kJ/mol from dynamic DSC analysis. Thermal stability and kinetics of thermal degradation were also studied by thermal gravimetric analysis (TGA). TGA results indicated that the temperature of POSSE/DDS system 5% weight loss is approximately 377.0°C, which is higher by 12.6°C than that of pure POSSER, and the primary degradation reaction (300–465°C) followed first order kinetics; the activation energy of degradation reaction is 75.81 kJ/mol.     

Cure kinetics of epoxy formulations of the type used in advanced composites

An analysis of the cure kinetics of three different formulations composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) epoxy resin and diaminodiphenyl sulfone (DDS) was performed. A series of isothermal tests was run, and the experimentally obtained results were checked against the proposed kinetic model. An autocatalyzed mechanism with the overall reaction order of 2 was found to adequately describe the cure kinetics. An increase in reaction rate was observed at higher temperature and higher DDS concentration. For a given formulation, the extent of reaction corresponding to the maximum reaction rate was independent of temperature. A secondary exotherm was detected, particularly in formulations with low DDS concentration, at approximately 40% conversion. At that point, the rate of primary amine–epoxide reaction decreases, and other reactions dominate the curing process. Such a mechanism is likely to cause a formation of an inhomogeneous thermoset morphology.