Kinetic Method by Using Calorimetry to Mechanism of Epoxy-Amine Cure Reaction

The thermokinetic behavior of the reaction between phenyl glycidyl ether and aniline closely resembles the analogous diepoxy diamine cure reaction in that the reactants are assembled before bond-breaking step occurs, and does not proceed through free reacting groups. The mechanism of the reaction between phenyl glycidyl ether and aniline in solventless system involves in addition to mechanism of the epoxy ring opening, structure changes accompanied by phase separation related to the self-aggregation. In an attempt to obtain further information about the reaction mechanism, the DSC heating runs of the reacted samples have been examined. These results suggest that the observed endothermic peaks are associated with additional ordering. The latter takes place only at lower temperature than reaction temperature. Since the rate constant k ₂ values for autocatalysed reaction follow of Arrhenius behavior, it is possible to calculate the activation energy, which is E=51 kJ mol^-1. Analysis of the kinetic experiments demonstrates that the heat of reaction that are detected in kinetic measurements provide correct information about the mechanism of the process. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermokinetics of the reaction of phenyl glycidyl ether with aniline

The thermokinetic curves in the reaction of phenyl glycidyl ether with aniline were calculated for various compositions of the reaction mixture and temperatures. In addition to the main exothermic effect related to the epoxide ring opening, another exothermic effect of unknown nature was observed. The kinetic data obtained are explained in terms of structural changes caused by the self-aggregation of the reaction product molecules. The “kinetic investigation” approach provides a quantitative analysis of calorimetric data.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 371–375, February, 2005     

Capacites calorifiques de durcisseurs amines et resines epoxydes

Heat capacities of some amines (aniline, N-methyl aniline, meta-phenylene diamine, diamino diphenyl methane, diamino diphenyl sulfone and diamino diphenyl oxide) and two epoxy resins (phenyl glycidyl ether and diglycidyl ether of bisphenol A) have been determined in the solid and liquid states versus temperature. The heat capacity increments related to the functional groups have been evaluated compared to references like benzene, aniline and phenyl glycidyl ether.     

Curing of epoxy-anhydride formulations in the presence of imidazoles

Differential scanning calorimetry was used to study the reaction of isomethyltetrahydrophthalic anhydride with phenyl glycidyl ether and the curing kinetics of diglycidyl ether of diphenylolpropane in the presence of imidazoles. The deformation-strength characteristics of cured epoxy polymers were determined.     

Calorimetric investigation of polymerization reactions. III. Curing reaction of epoxides with amines

The curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine as a model for the curing reactions were investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of reaction of phenyl glycidyl ether with butylamine is equal to 24.5 ± 0.6 kcal/mole. The rate of reaction was followed over the whole range of conversion for both model and curing reactions. The reactions are accelerated by the hydrogen-bond donor produced in the system. The rate constants based on the third-order kinetics were determined and discussed for the model reaction and for the chemically controlled region of curing reactions. The activation energies for these rate constants are 13-14 kcal/mole. At a later stage of conversion, the curing reactions become controlled by diffusion of functional groups. The final extent of conversion is short of completion for most isothermally cured and even for postcured samples because of crosslinking. It was quantitatively indicated that the final conversion of isothermal cure corresponds to the transition of the system from a viscous liquid to a glass on the basis of the theory of glass transition temperature of crosslinked polymer systems.     

Mechanism of the tertiary amine-catalyzed dicyandiamide cure of epoxy resins

Infrared and NMR data on tertiary amine-catalyzed, dicyandiamide—epoxy resin (and model compound) systems have been utilized to elucidate the mechanism of the curing process. The early exothermic curing reaction is shown to be ring opening of the resin epoxy groups by dicyandiamide imino and amino anionic species, giving rise to N-alkyl cyanoguanidines; a minor amount of polyether formation also occurs at this time. After the exothermic reaction is essentially complete at <90°C., a slow, high temperature (110–200°C.) addition of hydroxyl hydrogen across the nitrile triple bond occurs, giving rise to an imino ether which then rearranges to the guanyl urea.     

New facts concerning the reaction of K, K(15-crown-5)2 with phenyl glycidyl ether: unexpected formation of potassium cyclopropoxide

A new mechanism of the reaction of K⁻, K⁺(15-crown-5)₂ with phenyl glycidyl ether is presented. The linear ether bond is attacked only to a small extent, if at all. As the main reaction path the oxirane bond in the β-position is cleaved, followed by the γ-elimination of potassium phenoxide and the formation of potassium cyclopropoxide. Crown ether ring opening also occurs in reactions with organometallic intermediates.     

Study of chemical processes in the modification of epoxide polymers by aluminum oxide

The processes occurring during the modification of epoxy polymers by various polymorphic aluminum oxide modifications (γ-AlO(OH), γ-Al₂O₃, α-Al₂O₃) with epoxy groups were studied by the methods of IR Fourier spectroscopy, chemical analysis, and differential scanning calorimetry (DSC) by an example of a model compound (phenyl glycidyl ether). Two types of interactions were revealed: a direct chemical reaction of phenyl glycidyl ether with the surface hydroxy groups of alyminum oxide, and phenyl glycidyl ether homopolymerization. By processing by graphical method the data of chemical analysis on the diminishing in amount of epoxy groups in the course of the polycondensation reaction the value of activation energy 106–110 kJ mol⁻¹ of the process of phenyl glycidyl ether interaction with aluminum γ-oxide was determined.     

Acceleration mechanisms in curing reactions involving model systems

The mechanisms involving some of the most common accelerators in the curing reactions of epoxy resins have been investigated by use of model systems. Phenyl glycidyl ether was used as a model compound. The characterization of the reaction products was mainly carried out by High-Performance-Liquid-Chromatography and by preparative methods. Special attention was paid to the oligomerization reactions of the oxirane ring in the presence of tertiary amines. Three different types of oligomers depending on phenyl glycidyl ethers are discussed. The mechanisms of multifunctional accelerators such as imidazoles or phenol-MANNICH-base-compounds are much more difficult. The extraordinary interaction of imidazoles depends on the formation of different oligomers. Furthermore, the cleavage of the imidazole ring was observed. It is possible that the glycidyl ether oligomerization plays an important role in understanding the network structure. Some aspects of the accelerating effect of tertiary amines in the curing of glycidyl ethers with acid anhydrides were likewise discussed. The results obtained using these model reactions may be applied to influence the curing process in commercial epoxy resin systems.     

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.     

Kinetic and Quantum-Chemical Study of Oxirane Ring Cleavage with Acids

Kinetic and thermodynamic parameters of the reactions of phenyl glycidyl ether and epichlorohydrin with bis(alkylpolyethylene glycol) ether of orthophosphorus acid (oxyphos KD-6) are established. It is shown that the difference in the reactivity of the oxiranes is caused by the electronic effects of substituents and the protonation by the phenolic oxygen atom of phenyl glycidyl ether. Basic solvents decrease the reactivity of the systems. Based on AM1 semiempirical quantum-chemical calculations, a hydroxycarbocation mechanism of the oxirane ring opening was proposed, involving initial formation of unstable cis- and trans-oxonium structures.     

Reactivity of silicon‐based epoxy monomers as studied by near‐infrared spectroscopy and multivariate curve resolution methods

The reaction of glycidyloxydimethylphenyl silane with aniline was used as a model system to study the reactivity of silicon‐based epoxy monomers. The reaction was monitored online by near‐infrared spectroscopy, and the evolution of the concentration of each species throughout the reaction was determined by the application of multivariate curve resolution/alternating least squares to the set of recorded spectra. The reactivity was evaluated by a comparison of the concentration profiles obtained for the glycidyloxydimethylphenyl silane/aniline system with those of phenylglycidyl ether/aniline as a reference system. The results confirmed that the reactivity of the silicon‐based epoxy monomer was higher and that its ring opening reaction was faster because of electronic effects. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1447–1456, 2006     

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.     

Cleavage of different ether bonds in butyl glycidyl ether and allyl glycidyl ether by K, K(15-crown-5)2

The kind of substituent in alkyl glycidyl ethers affects the course of their reaction with K⁻, K⁺(15-crown-5)₂. The cyclic oxirane ring is exclusively cleaved in the case of butyl glycidyl ether whereas the presence of the unsaturated allyl group in the glycidyl ether molecule unexpectedly prefers the scission of the linear ether bond. In both the systems organometallic intermediates are formed. They react with crown ether causing its ring opening. Allylpotassium formed from allyl glycidyl ether reacts also with another glycidyl ether molecule; the oxirane ring is opened in this case.     

Design and synthesis of multifunctional glycidyl ethers that undergo frontal polymerization

An investigation of the photoactivated cationic ring‐opening frontal polymerizations of a series of alkyl glycidyl ethers has been carried out with the aid of a novel technique, optical pyrometry. With this technique, the effects of the monomer structure on the frontal behavior of these monomers have been examined. Upon irradiation with UV light, the photopolymerizations of many alkyl glycidyl ethers display a prolonged induction period at room temperature as the result of the formation of long‐lived, relatively stable secondary oxonium ions. The input of only a small amount of thermal activation energy is required to induce the further reaction of these species with a consequent autoaccelerated exothermic ring‐opening polymerization. Photoactivated frontal polymerizations have been observed for both mono‐ and polyfunctional alkyl glycidyl ether monomers. The ability of monomers to exhibit frontal behavior has been found to be related to their ability to stabilize the secondary oxonium ion intermediates through multiple hydrogen‐bonding effects to the ether groups present in the molecule. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6435–6448, 2006     

含环氧基团的聚合物微球固载2,2,6,6-四甲基哌啶氮氧自由基催化剂的制备及其催化分子氧氧化苯甲醇

以甲基丙烯酸缩水甘油酯(GMA)为单体, 以乙二醇二甲基丙烯酸酯(EGDMA)为交联剂, 采用悬浮聚合法制得交联聚甲基丙烯酸缩水甘油酯(CPGMA)微球, 然后以4-羟基-2,2,6,6-四甲基哌啶氮氧自由基(4-OH-TEMPO)为试剂, 使CPGMA微球表面的环氧基团发生开环反应, 从而制得了TEMPO固载化微球TEMPO/CPGMA, 考察了制备条件对固载化反应的影响, 并采用多种方法对微球TEMPO/CPGMA进行了表征. 将微球TEMPO/CPGMA与CuCl组成共催化体系, 用于分子氧氧化苯甲醇, 考察了反应条件对催化体系性能的影响. 结果表明, 以含环氧基团的聚合物微球CPGMA为载体, 通过开环反应, 可成功地实现TEMPO的固载化, 开环反应属S_N2亲核取代反应, 适宜采用溶剂N,N''-二甲基甲酰胺和反应温度85℃. 非均相催化剂TEMPO/CPGMA与助催化剂CuCl构成共催化体系, 在室温、常压O₂条件下可高效地将苯甲醇氧化为苯甲醛, 产物选择性和产率分别为100%和90%. 主催化剂TEMPO与助催化剂CuCl适宜的摩尔比为1:1.2; 主催化剂适宜用量为0.90 g. 此外, TEMPO/CPGMA固体催化剂具有良好的循环使用性能.     

Reaction thermodynamics of amine‐cured epoxy systems: Validation of the enthalpy and heat capacity of reaction as determined by modulated temperature differential scanning calorimetry

The reaction enthalpy and reaction heat capacity of three aromatic epoxy–amine systems have been determined with modulated temperature diffential scanning calorimetry (MTDSC), mostly in quasi‐isothermal conditions, over a wide temperature range (33–140 °C) and for different mixture compositions. The reaction enthalpy is only slightly dependent on the epoxy–amine chemistry, from ?111 to ?98 kJ/mol epoxy functionality. With the model system phenyl glycidyl ether (PGE)+aniline, the reaction enthalpy of the secondary amine–epoxy reaction step is equal to that of the primary amine–epoxy reaction. Group contributions needed to calculate the reaction heat capacity with an additivity approach are evaluated, and a new value of 37.2 J mol^?1 K^?1 for the group N? (H)(C)(CB) is proposed. With this group contribution, the additivity method predicts almost equal values for the reaction heat capacity of both amine–epoxy reaction steps at 298.15 K (Δ_rC_p,prim = 15.7 J mol^?1 K^?1 and Δ_rC_p,sec = 14.6 J mol^?1 K^?1), whereas the experimental value of Δ_rC_p,sec is about three times larger than that of Δ_rC_p,prim at 100 °C. These results are confirmed experimentally for PGE+aniline as a different temperature dependence of both reaction heat capacities. MTDSC therefore is potentially interesting for differentiating between reactive species in an epoxy–amine reaction, a benefit previously assigned to spectroscopic methods only. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 594–608, 2003     

Anhydride curing of epoxy resins via chain reaction

In contrast to common curing reactions, the anhydride curing of epoxies follows a living anionic chain growth. The resulting consequences of this mechanism, i.e. (1) DP_n = a[M_o]/[I_o], (2) first-order kinetics and (3) Poisson chain-length distribution were tested with the phenyl glycidyl ether/phthalic acid anhydride system, using l-methyl imidazole. Overall agreement was found and the observed deviations could be explained with a modified Poisson process. Conformational properties of the resins were measured by static and dynamic light scattering and by viscometry. These were compared with the quantities of a corresponding branched system prepared with a mixture of phenyl glycidyl ether and bisphenol-A diglycidyl ether. Typical deviations to smaller dimensions were observed at high molar masses as a result of increasing branching.     

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.     

Cationic photopolymerization of alkyl glycidyl ethers

An investigation of the photoactivated cationic ring‐opening frontal polymerizations of a series of alkyl glycidyl ethers was carried out with the aid of a novel technique, optical pyrometry. With this technique, the effects of various experimental parameters, such as the photoinitiator type and concentration, as well as the effects of the monomer structure on the frontal behavior of these monomers were examined. Upon irradiation with UV light, the photopolymerizations of many alkyl glycidyl ethers displayed a prominent induction period at room temperature as the result of the formation of long‐lived, relatively stable secondary oxonium ions. The input of only a small amount of thermal activation energy was required to induce the further reaction of these species with the consequent autoaccelerated exothermic ring‐opening polymerization. Photoactivated frontal polymerizations were observed for both mono‐ and polyfunctional alkyl glycidyl ether monomers. The ability of monomers to exhibit frontal behavior was found to be related to their ability to stabilize the secondary oxonium ion intermediates through hydrogen‐bonding effects. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3036–3052, 2006