Kinetics and mechanism of the epoxide-amine polyaddition

The mechanism and kinetics of the epoxide-amine polyaddition reaction have been studied by isothermal and scanning DSC measurements. The initial concentrations of the reactants (epoxides: bisphenol-A-diglycidyl ether (DGEBA) and phenyl glycidyl ether (PGE), amines: N,N′-dibenzylethylenediamine (DBED) and aniline) in our model systems have been strongly varied. The suggested kinetic model describes the reaction behavior of mixtures with any initial epoxide/amine ratios over the whole range of cure by a single parameter set. To find the optimum kinetic parameters, we have solved the set of differential equations numerically by the technique of multivariate non-linear regression (Mult-NLR). Excellent agreement was obtained between calculated and experimental curves.     

Synthesis and characterization of an epoxy based thermoset containing a fluorinated thermoplastic

A novel fluorinated thermoplastic (FT) was synthesized from diglycidyl ether of bisphenol A (DGEBA), and 3‐(trifluoromethyl)aniline. FT was found to be miscible with DGEBA as shown by the existence of a single glass transition temperature (T_g) within the whole composition range. On the basis of several experimental techniques, it was found that upon heating etherification reaction takes place between FT and DGEBA. A DGEBA‐aromatic diamine (4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) formulation was modified with the FT. The influence of FT on the epoxy‐amine kinetics was investigated. Both structural parameters, gelation, and vitrification, were found to be affected by etherification reaction between epoxy and hydroxyls groups belonging to FT. The presence of ether linkages induced system stoichiometry modification. In addition, the curing conditions influence on FT migration towards the surface was studied on samples prepared with 20 wt % of modifier. SEM–EDX analysis confirmed that modified systems exhibits notable fluorine enrichment within the uppermost 200 μm. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2781–2792, 2007     

Effect of stoichiometry and diffusion on an epoxy/amine reaction mechanism

The bulk phase kinetics of an epoxy (DGEBA) /amine (DDS) thermoset have been studied using DSC, FTIR, and ¹³C-NMR. In the absence of catalyst, the reaction was found to involve a main exothermic reaction between epoxide and amine hydrogen and a side reaction between tertiary amine formed in the main reaction and epoxide. The main reaction was exothermic while the side reaction had no discernable exotherm. Etherification did not occur to any significant extent. Since only the main reaction is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydrogen were consumed at different rates as a way of following the side reaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above mechanism by identifying the formation of a quaternary ammonium ion/alkoxide ion pair as a reaction product of tertiary amine and epoxide. This mechanism has been successfully fit to a rate law valid over the entire extent of reaction. The rate constant for the epoxy/amine addition reaction was found to depend on hydroxide concentration (extent), reaction temperature, and glass transition temperature and included contributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not affect the overall system T_g. Both reactions were second order. The rate constants for the main reaction first increase with increasing extent due to autocatalysis by hydroxide before decreasing due to the diffusion limit caused by gelation and vitrification. © 1995 John Wiley & Sons, Inc.     

High resolution solid‐state 13C‐NMR study of as‐cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the physico‐chemical modifications of aliphatic or aromatic amine‐cured epoxy resins based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins have a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid‐state ¹³C‐NMR spectroscopy we show that the aliphatic amine‐cured resin (DGEBA‐TETA) appears much more sensitive to gamma rays than the aromatic amine‐cured one (DGEBA‐DDM). On the one hand, qualitative analyses of the high resolution solid‐state ¹³C‐NMR spectra of both epoxy resins, irradiated under similar conditions (8.5 MGy), reveal almost no change in the aromatic amine‐cured resin whereas new resonances are observed for the aliphatic amine‐cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acids and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are investigated by measuring the relaxation times, T_CH, T_1ρH and T_1C , before and after irradiation. The study of relaxation data shows the formation, under irradiation, of a more rigid network, especially for the aliphatic amine‐cured system and confirms that aromatic amine‐cured resin [DGEBA‐4,4′‐diaminodiphenylmethane(DDM)] is much less affected by ionizing radiations than the aliphatic amine‐cured resin [DGEBA‐triethylenetetramine(TETA)]. Moreover, it has been shown that the molecular modifications generated by irradiation on the powder of the aliphatic‐amine‐cured resin appear to be homogeneously distributed inside the polymers as no phase separations can be deduced from the above analyses. Copyright © 2001 John Wiley & Sons, Ltd.     

Fluorescence probe-label methodology for in situ monitoring network forming reactions

The curing of the stoichiometric reaction mixture diglycidyl ether bisphenol A (DGEBA) with N-methylethylenediamine (MEDA) and BEPOX 1268 formulation was monitored by FTIR (in the near IR region) and by fluorescence spectroscopy. 5-Dimethylamino-1-naphthalenesulfonamide derivatives and 4-dialkylamino-4^′-nitrostilbene structural units were used as labels and/or probes. It has been proved that hardener in BEPOX 1268 formulation consists of amine containing the primary and secondary amino group. The rate constant for the addition reaction of the secondary amino hydrogen to epoxide is approximately two times larger than that of the primary amino group hydrogen in MEDA and several times (∼seven times) lower in the amine component of BEPOX 1268 formulation. The changes in the integrated fluorescence intensity of the label during the epoxy groups conversion indicate the most important changes in chemical transformations of the reaction mixture, i.e. primary reaction of the secondary amino groups, the gel point (DGEBA-MEDA) and entry of the system to the glassy state (for DGEBA-MEDA and BEPOX 1268). The change in slope of the fluorescence half bandwidth dependence on the epoxy groups conversion indicates the maximum concentration of the secondary amino groups in the reaction mixture (BEPOX 1268). It has been shown that the dependence of the first moment of the emission band vs. epoxy groups conversion can be used to determine the epoxy groups conversion in situ and in real time.     

Curing properties of novel curing agent based on phenyl bisthiourea for an epoxy resin system

Phenyl bisthioureas: 4,4′-(bisthiourea)diphenylmethane (DTM), 4,4′-(bisthiourea)diphenyl ether (DTE), and 4,4′-(bisthiourea)diphenyl sulfone (DTS) were synthesized and used as curing agents for the epoxy resin diglydicyl ether bisphenol A (DGEBA). Synthesized phenyl bisthioureas were characterized using FT-IR and ¹H-NMR analysis. For comparison studies the epoxy system was also cured using the conventional aromatic amine 4,4′-diaminodiphenyl ether (DDE). Curing kinetics of epoxy/amine system was studied by dynamic and isothermal differential scanning calorimeter (DSC). Curing kinetic was evaluated based on model-free kinetics (MFK) and ASTM E 698 model, and the activation energy was compared with DDE. Curing system of phenyl bisthiourea link (DGEBA/DTM, DGEBA/DTE, and DGEBA/DTS) shows two exothermic peaks, while that of the conventional aromatic amines showed only a single peak. The initial exothermic peak is due to the primary nitrogen of the thiourea group, and the exotherm at higher temperature is due to the presence of thiourea groups. Glass transition temperature (T _g) of DGEBA/DTM, DGEBA/DTE, and DGEBA/DTS cured resins were lowered by 323 K when compared to the widely used diaminodiphenyl ether (DDE) cured resin. Oxidation induction temperature measurement performed on DSC suggests that the DGEBA/DTM, DGEBA/DTE, and DGEBA/DTS system cured resins has better oxidative stability when compared to cured DGEBA/DDE resin system.     

Curing of linear and crosslinked epoxy systems: A fluorescence study with dansyl derivatives

The curing of diglycidyl ether of bisphenol A (DGEBA) with N,N′-dimethylethylenediamine (N,N′-DMEDA) or ethylenediamine (EDA) was monitored by fluorescence spectroscopy and Fourier transform infrared (in the near-infrared region). 5-Dimethylamino-naphthalene-1-sulfonamide (DNS) derivatives were used as probes (fluorophores added to the reaction mixture) and labels (fluorophores attached by covalent bonds to diglycidyl reactants). The term containing the ratio of the reaction rate constants for the addition of the secondary and primary amine hydrogens to the epoxide was included in the reduced reaction rate term for the autocatalyzed and catalyzed epoxide curing reactions. The changes in the integrated fluorescence intensities of the labels during the epoxy group conversion indicated, in some cases, the most important changes in the chemical transformations of the reaction mixture: the epoxy group conversion, during which a rapid increase in the tertiary amino group concentration was first observed; the gel point (for EDA); and the entry of the system into the glassy state (for N,N′-DMEDA and EDA). The fluorescence probes monitored neither the gel point nor the threshold of the glassy state. For the DGEBA–N,N′-DMEDA system, a wavy dependence of the integrated fluorescence intensities of the DNS labels on the epoxy group conversion might reflect the molar concentrations of polymer homologues (referred to the initial number of moles in the system) in the reaction mixtures of the diepoxide and secondary diamine. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 64–78, 2004     

Curing kinetics and thermal stability of diglycidyl ether of bisphenol

Curing kinetics of diglycidyl ether of bisphenol-A (DGEBA) in the presence of varying molar ratios of aromatic imide-amines and 4,4′-diaminodiphenylsulfone (DDS) were investigated by the dynamic differential scanning calorimetry. The imide-amines were prepared by reacting 1 mole of benzophenone 3,3′,4,4′-tetracarboxylic acid dianhydride (B) with 2.5 moles of 4,4′-diaminodiphenyl ether (E)/ or 4,4′-diaminodiphenyl methane (M)/ or 4,4′-diaminodiphenylsulfone (S) and designated as BE/ or BM/ or BS. The mixture of imide-amines and DDS at ratio of 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25 and 1:0 were used to investigate the curing behaviour of DGEBA. The multiple heating rate method (5, 10, 15 and 20°C min⁻¹) was used to study the curing kinetics of epoxy resins. The peak exotherm temperature was found to be dependent on the heating rate, structure of imide-amines as well as on the ratio of imide-amine: DDS used. A broad exotherm was observed in the temperature range of 180–230°C on curing with mixture of imide-amines and DDS. Curing of DGEBA with mixture of imide-amines and/or DDS resulted in a decrease in characteristic curing temperatures. Activation energy of curing reaction as determined in accordance to the Ozawa’s method was found to be dependent on the structure of amine. The thermal stability of the isothermally cured resins was also evaluated using dynamic thermogravimetry in a nitrogen atmosphere. The char yield was highest in case of resins cured using mixture of DDS: BS (0.25:0.75; EBS-3), DDS: BM (0.5: 0.5; EBM-2) and DDS: BE (0.5: 0.5; EBE-2).     

Controlled shrinkage polymers: Characterization of epoxy resins cured with spirobislactones

The diglycidyl ether of bisphenol A (DGEBA) was cured with either an aliphatic or an aromatic spirobislactone using a tertiary amine catalyst. The products were characterized by FTIR, TGA, DSC, dilatometry, and single-fiber adhesion measurements, and their performance was compared to that of DGEBA cured with acid anhydrides. Both aliphatic and aromatic bislactones are effective curing agents for DGEBA. FTIR and dilatometry confirm that both lactone rings open early in the curing reaction and initially offset shrinkage caused by polymerization. After the bislactone has been consumed, oxirane reactions proceed in a normal fashion. The final shrinkage of cured DGEBA polymers, with or without addition of bislactones, is 3.0–3.5%. Bislactone-modified materials possess superior thermal properties, when compared to those of anhydride-cured materials.     

Novel,environmentally friendly crosslinking system of an epoxy using an amino acid: Tryptophan‐cured diglycidyl ether of bisphenol A epoxy

Tryptophan, an amino acid, has been used as a novel, environmentally friendly curing agent instead of toxic curing agents to crosslink the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The curing reaction of tryptophan/DGEBA mixtures of different ratios and the effect of the imidazole catalyst on the reaction have been evaluated. The optimum reaction ratio of DGEBA to tryptophan has been determined to be 3:1 with 1 wt % catalyst, and the curing mechanism of the novel reaction system has been studied and elucidated. In situ Fourier transform infrared spectra indicate that with the extraction of a hydrogen from NH₃⁺ in zwitterions from tryptophan, the formed nucleophilic primary amine and carboxylate anions of the tryptophan can readily participate in the ring‐opening reaction with epoxy. The secondary amine, formed from the primary amine, can further participate in the ring‐opening reaction with epoxy and form the crosslinked network. The crosslinked structure exhibits a reasonably high glass‐transition temperature and thermal stability. A catalyst‐initiated chain reaction mechanism is proposed for the curing reaction of the epoxy with zwitterion amino acid hardeners. The replacement of toxic curing agents with this novel, environmentally friendly curing agent is an important step toward a next‐generation green electronics industry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 181–190, 2007     

Optically clear simulataneous interpenetrating polymer networks based on poly(ethylene glycol) diacrylate and epoxy. II. Kinetic study

Simultaneous interpenetrating polymer networks (SINs) based on diglycidyl ether of bis-phenol A (DGEBA) and poly(ethylene glycol) diacrylate (PEGDA) in weight ratios of 100/0, 50/50, and 0/100 were blended and cured simultaneously by using benzoyl peroxide (BPO) and m-xylenediamine (MXDA) as curing agents. A kinetic study during SIN formation was carried out at 45, 55, 63, and 70°C. Concentration changes for both the epoxide and C?C bond were monitored with FTIR. A rate expression for DGEBA cure kinetics was established with a model reaction of phenyl glycidyl ether (PGE) and benzylamine. Experimental results revealed that lower rate constants and higher activation energy for the SIN were found, compared with those for the constituent DGEBA and PEGDA network formation. A model of network interlock was proposed to account for this phenomenon. During simultaneous cure of DGEBA and PEGDA, the interlock (mutual entanglement) between DGEBA and PEGDA networks provided a sterically hindered environment, which subsequently increased the activation energy and reduced cure rates for both DGEBA and PEGDA. © 1993 John Wiley & Sons, Inc.     

Effect of aromatic substitution on the cure reaction and network properties of anhydride cured triphenyl ether tetraglycidyl epoxy resins

A systemic study of the impact of aromatic substitution on the reaction rate and network properties of the isomers of a tetraglycidylaniline triphenyl ether epoxy resin cured with anhydride hardeners is presented here. The epoxy resins synthesized in this work were based upon N,N,N,N‐tetraglycidyl bis(aminophenoxy)benzene (TGAPB), where the glycidyl aniline and ether groups change from being all meta (133 TGAPB), to meta and para (134 TGAPB), and finally to an all para substituted epoxy resin (144 TGAPB). Increasing para substitution increased reaction rate, promoted the onset of vitrification and increased epoxide conversion. Thermal properties such as glass transition temperatures (T_g) and coefficients of thermal expansion (CTE) both increased consistently with increasing para substitution, although thermal stability as measured via thermogravimetric analysis decreased. Mechanical properties also varied systematically with flexural strength and ductility increasing with increased para substitution, while the modulus decreased. Indeed, the ductility almost doubled, as measured by the work of fracture and displacement at failure highlighting the importance of substitution on properties.     

Mechanical relaxations in episulfide network polymers

A variety of condensation network polymers have been prepared by the reaction between amine, episulfide, and epoxide monomers. The mechanical relaxations occurring in these systems have been examined using a torsion pendulum and the role of hydrogen bonding in the mechanism of the β relaxation is shown to be insignificant. The chemical reaction between amine and episulfide groups has been investigated by IR spectroscopy and is shown to parallel the reaction between amine and epoxide groups. However, steric and electronic factors are suggested to decrease the extent of reaction when aromatic amines are involved. In the case of networks prepared from blends of episulfide and epoxide monomers, measurements of the gel time, together with the mechanical behavior around the glass transition, indicate that either interpenetrating or two-phase networks are formed. This is postulated to be a consequence of the high reactivity of the episulfide ring compared to the epoxide ring. The blending of small amounts of episulfide monomer with the epoxide monomer prior to curing may provide an effective method for lowering gel times without reducing the crosslink density and its dependent physical properties.     

The relative reactivity of primary and secondary amine hydrogen atoms of aromatic amines with epichlorohydrin and N- and O-glycidyl compounds

The relative value of the rate constants for the reactions between the secondary and primary amine hydrogen atoms of 3-trifluoromethylaniline with epichlorohydrin, and of aniline with phenyl glycidyl ether and with some N-alkyl-N-glycidylanilines were determined by HPLC analysis. Values ranged from 0.14 to 0.24 and are in agreement with the findings of earlier workers for the reactions of aromatic amines with O-glycidyl compounds but in direct conflict with the claim of a recent publication. The value for the reaction between 3-trifluoromethylaniline and epichlorohydrin was unaffected by the nature of the catalyst, which covered a wide range of strengths and steric requirements.     

Epoxy/POSS organic-inorganic hybrids: ATR-FTIR and DSC studies

Organic-inorganic hybrid nanocomposites were prepared by reaction of an octaepoxy-silsesquioxane, OECh, with an epoxy-amine system. OECh was used to partially replace the thermosetting resin, diglycidyl ether of bisphenol A, DGEBA, in its reaction with an aromatic diamine, 4,4′-(1,3-phenylenediisopropylidene) bisaniline, BSA. The OECh was characterized by different techniques. The curing kinetics of ternary systems formed by DGEBA, OECh and BSA, was followed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy, ATR-FTIR. All the mixtures were prepared with a stoichiometric ratio between epoxy and amine groups. The degree of reaction of glycidyl epoxy ring along the curing cycle selected was obtained from the infrared spectra. A peak-height method based on the ratio of the height of the characteristic to reference absorbance peak was used. The curing kinetic of different blends was obtained by differential scanning calorimetry, DSC. Three different methods, the differential of Kissinger, the integral of Flynn-Wall-Ozawa and the phenomenological model of Kamal, were used in order to obtain the kinetic parameters of the cure reaction. It is observed that the presence of POSS accelerates the rate of opening of glycidyl epoxy rings from DGEBA. The behaviour of the mixture during the curing process can be explained with an autocatalytical model, corrected with the contribution of the diffusion of the molecules during the course of the reaction.     

Synthesis and curing of amino‐containing benzoxazine as a novel hardener for diglycidyl ether of bisphenol‐A

Benzoxazines containing various additional functional groups have been extensively reported to improve the properties of polybenzoxazines. In this work, a novel amino‐containing benzoxazine (PDETDA‐NH₂) was conveniently synthesized from diethyltoluenediamine (DETDA), 2‐hydroxybenzaldehyde, and paraformaldehyde and was used as a hardener for diglycidyl ether of bisphenol‐A (DGEBA). The curing behaviors of PDETDA‐NH₂ and PDETDA‐NH₂/DGEBA systems were studied by DSC, FT‐IR, and ¹H NMR. When curing, PDETDA‐NH₂ was firstly polymerized to N,O‐acetal‐type polymer and then rearranged to Mannich‐type polymer at elevated temperature, while the addition reaction between amino and benzoxazine was discouraged because of the steric hindrance of alkyl substituents. During PDETDA‐NH₂/DGEBA curing, it was found that the reactions happened in the order of addition polymerization of amino and epoxide, ring‐opening polymerization of benzoxazine, etherification between phenolic hydroxyl of the polymerized benzoxazine, and epoxide. Compared with DETDA cured DGEBA, PDETDA‐NH₂ cured DGEBA showed higher modulus, higher char yield, and much lower water uptake.     

2-(氨基苯基)六氟异丙醇衍生物的合成

以六氟丙酮三水合物和芳香胺为原料,合成了一系列2-芳胺基六氟异丙醇化合物。研究了反应中原料配比、催化剂种类及用量、溶剂种类、反应时间及取代基对反应的影响。结果表明,在六氟丙酮三水合物用量为90 mmol,芳香胺用量为30 mmol,对甲基苯磺酸为催化剂,其用量为苯胺物质量的6%时,回流反应5～35h,反应的转化率和收率分别高达40.1%～100.0%,39.0%～99.0%。同时本文对六氟丙酮三水合物和无水六氟丙酮与苯胺的反应机理进行了比较,推测了六氟丙酮三水合物与苯胺的反应历程,并通过对其中间产物结构的表征进一步确认了该历程。     

Mass spectrometric characterization of telechelic prepolymers and addition polymers of DGEBA–aliphatic amines

Plasma desorption (PD) mass spectra of high molecular weight addition polymers of 2.2-bis-[4-(2.3-epoxypropoxy)phenyl]propane (DGEBA) and benzylamine show protonated molecular ions of the intact polymers and oligomer molecules. In the spectrum of a DGEBA/N,N′-dibenzyl-5-oxanonanediamine-1.9 addition polymer only fragments of the oligomers and a cyclic oligomer are observed. In both polymer spectra there is no indication for side reactions during the addition polymerization such as ether formation. Fast-atom bombardment (FAB) spectra of telechelic prepolymers having amino end groups show the regular oligomers with increasing degree of polymerization and the expected fragmentation products. Only prepolymers with epoxide end groups contain the regular prepolymers as well as side reaction products which are formed by reactions of the telechelics and DGEBA or by reaction of themselves. © 1996 John Wiley & Sons, Inc.     

Differences in structure growth in amine curing of diglycidyl ether of bisphenol a and N,N-diglycidylaniline epoxy resins: Bifunctional models

The reaction of diepoxides, diglycidylaniline (DGA), or diglycidyl ether of Bisphenol A (DGEBA) with aniline was followed using HPLC and SEC. The effect of molar ratio of reagents, dilution of the system, reaction temperature, and the difference between the reaction mechanisms for DGA and DGEBA systems on the reaction kinetics and molecular weight evolution is discussed. Molecular weights of the DGA-aniline polymers were by an order of magnitude lower than those of the DGEBA-aniline polymers due to the formation of small cyclic products in the former case. Also, a reduction in M_n with increasing temperature, dilution, and diluent polarity is brought about by a greater tendency toward cyclization under these conditions. Theoretically calculated molecular weight evolution during the reaction is in satisfactory agreement with the experiment. © 1995 John Wiley & Sons, Inc.     

Relative reactivity of primary and secondary amine hydrogen atoms in the reaction between aniline and phenyl glycidyl ether: The effect of ethanol and other additives and the modifying effect of benzene as solvent

The relative reactivity ratio (k₂/k₁) for the secondary and primary amine hydrogen atoms in the neat reaction between aniline and phenyl glycidyl ether was 0.30. This is significantly lower than a recently reaffirmed random value of 0.5 for this system. The ratio is sensitive to added ethanol and decreased with increasing concentration to a limiting value of about 0.20. With benzene as solvent, the effect of added ethanol was more complex, and a low concentration provided a value of 0.45 which decreased with increasing concentration. Other hydroxy additives behaved similarly, but boron trifluoride appears to have no effect on this ratio.