Synthesis and curing behavior of novel multifunctional hybrid oligomers

Novel multifunctional hybrid vinylized epoxide oligomers (MVEOs) containing two different reactive groups were synthesized through the esterification of tetraglycidyl 4,4′‐diaminodiphenylmethane (TGDDM) with acrylic acid (AA) at various molar ratios. The changes of vinyl ester and epoxy groups in MVEOs were studied by Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance, and Gel permeation chromatograph. It was found that more amount of AA in the reactant would increase the contents of vinyl ester and molecular weight. The curing behavior of MVEOs has been studied by scanning differential scanning calorimetry (DSC). Two distinct exothermic peaks were observed in the MVEOs which can be attributed to the radical polymerization of vinyl ester/styrene and condensation polymerization of epoxy/MeTHPA, respectively. Two different kinds of curing programs have influenced each other which makes the exothermic peaks overlapped. The DSC scan of MVEO‐2 indicated that the radical initiated curing reaction of vinyl ester won't notably affect the curing of epoxy without MeTHPA. However, the thermal curing of vinyl ester in MVEO‐2 without MEKP/Co would be occurred with the temperature rising. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42276.     

Preparation and nonisothermal cure kinetics of DGEBA‐nanosilica particles composites

Nanocomposites from nanoscale silica particles (NS), diglycidylether of bisphenol‐A based epoxy (DGEBA), and 4,4′‐diaminobiphenyl benzidine (DAPB) as curing agent were obtained from direct blending of these materials. This homogenous mixture was cured in the oven at a particular temperature for a certain time or scanned from room temperature up to 300°C in differential scanning calorimeter (DSC). Mechanism and kinetic of the cure reaction of nanocomposite and thermal stability of the cured sample were studied with FTIR, DSC, and thermogravimetric analysis, respectively. The effect of amount of nanosilica (NS) particles as catalyst on the cure reaction of DGEBA/DAPB system was studied by the Kissinger and Ozawa equations. The existence of NS particles with hydroxyl groups in the structure catalyzes the cure reaction of DGEBA/DAPB system, increased the rate constant, and shifted the exothermic peak toward lower temperatures with increasing amount of NS particles. The activation energies of cure reaction of pure DGEBA/DAPB system obtained from two methods were in good agreement and decreased when NS particles were present in the mixture. The isothermal cure reaction at 145°C in an oven was followed by measuring the disappearance peak of epoxide group at 916 cm⁻¹ using FTIR. The diffusive behavior of cured samples was investigated during water sorption at 25°C and the experimental results fitted well according to Fick's law. Diffusion coefficient of cured sample containing 10% NS decreased in comparison to the sample without NS particles. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

Cure behavior and properties of an epoxy resin modified with a bismaleimide resin

A bismaleimide (BMI) resin was added to an epoxy system composed of N,N′-tetraglycidyldiaminodiphenyl methane (TGDDM) and diaminodiphenyl methane (DDM). Cure behavior of the BMI modified epoxy resins was studied by a dynamic differential scanning calorimetry (DSC) method. Dynamic DSC thermograms of the BMI modified epoxy resins indicated unimodal reaction exothermic peaks. The overall heat of reaction per unit mass decreased with BMI composition. The residual heat of reactions of the epoxy blends cured at 180°C for 3 h increased with BMI composition. Thermal stability of the epoxy system improved by incorporating BMI resin. Flexural strength and modulus increased with BMI composition.     

Cure and reaction kinetics of an anhydride‐cured epoxy resin catalyzed by N‐benzylpyrazinium salts using near‐infrared spectroscopy

The cure behavior and the reaction kinetics of an anhydride‐cured epoxy resin catalyzed by cationic thermal latent initiator, N‐benzylpyrazinium salts, have been investigated by a near‐infrared (NIR) spectroscopy. The spectral changes are interpreted in terms of the mechanism of cure. NIR absorption bands are due to protons connected to carbon, nitrogen, and oxygen. In this work, the homogeneous model system involves a simple addition reaction mechanism leading to an exothermic reaction between epoxide and anhydride activated groups. A comprehensive account of the origin, location, and shifts during reaction of all major NIR absorption peaks in the spectral range from 4000 to 7100 cm^?1 is provided. The extent of reaction is calculated from NIR absorption band at 4530 cm^?1, which depends on epoxide concentration. The utility of NIR spectroscopy to study the kinetics of epoxy cure reaction has been established. Consequently, absorbencies in the NIR spectra suitable for quantitative studies of epoxy resin reaction kinetics have been identified.     

Cure kinetics of epoxy/anhydride nanocomposite systems with added reactive flame retardants

Montmorillonite nanocomposite systems obtained from epoxy cured using anhydride and the addition of a reacting flame retardant are studied in this paper. In particular, a thermokinetic analysis of the behavior of five different compounds was performed, using a differential scanning calorimeter. The isothermal tests showed double reaction peaks, due to the cure reactions of DGEBA/acid anhydride systems. The comparisons between dynamic thermograms (and between isothermal ones, too) for the different mixtures also showed that the addition of other active substances (such as a nanofiller or a flame retardant additive) does not change the mechanism of crosslinking from a qualitative point of view, but both the nanoreinforcement and the flame retardant seemed to exert an evident catalytic action on the cure reactions. A model describing the cure behavior of the aforementioned materials is proposed in this work. This model takes into account the fact that the reaction mechanism of each analyzed system is composed of a couple of parallel phenomena: the fast opening of anhydride ring (corresponding to a first exothermic peak and characterized by “n‐th order” kinetics) and resin networking (corresponding to a second exothermic peak and characterized by an “auto‐catalytic with zero initial velocity” behavior). The verification of the proposed model was performed by means of a comparison between experimental data (normalized curves derived from DSC thermograms) and theoretical data (derived from a numerical integration—using the second order Runge–Kutta method—of the model‐representative equation) and provided very good results. This allows one to apply such a model to any engineering process problem concerning the cure of DGEBA/acid anhydride/phyllosilicate nanocomposite systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1676–1689, 2004     

Cure kinetics of a low epoxide/hydroxyl group-ratio bisphenol a epoxy resin–anhydride system by infrared absorption spectroscopy

An infrared absorption spectroscopy study of the curing kinetics of a low (1.12) epoxide/hydroxyl-group ratio bisphenol A epoxy resin—phthalic anhydride system is reported. A full infrared peak assignment to molecular vibrational modes is given for the range 400 to 4000 cm^?1, and the optical density behavior of all peaks during reaction is discussed in detail. Proposed rival reaction mechanisms are considered and their respective kinetic behavior discussed. The reaction was found to follow consecutive-step addition esterification and simultaneous addition etherification, and epoxide—hydroxyl group and carboxylic acid dimer hydrogen bonding was found to occur. The reaction behavior supports a proposed hydroxyl group-limited inhomogeneous bulk reaction mechanism of a colloid type.     

Multifunctional formaldehyde resins as curing agent for epoxy resins

Formaldehyde resins (FR) at 1/1/2 molar ratios of monomers (Cl‐phenol/amino monomers/p‐formaldehyde) were synthesized under acid catalysis. The obtained resins were characterized using elemental analysis, FTIR and RMN spectroscopic methods, being used as crosslinking agents for epoxy resin formulations. The curing of epoxy resins with FR were investigated. The glass transition temperature (T_g) and decomposition behavior of crosslinked resins were studied by differential scanning calorimetry (DSC) and thermogravimetric (TGA) techniques. All DSC scans show two exothermic peaks, which implied the occurrence of cure reactions between epoxy ring and amine or carboxylic protons, in function of chemical structures of FR. The crosslinked products showed good thermal properties, high glass transitions, and low water absorption. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Intra‐ and extra‐gallery reactions in tri‐functional epoxy polymer layered silicate nanocomposites

Achieving a high degree of exfoliation in epoxy‐based polymer layered silicate (PLS) nanocomposites is crucial to their successful industrial application, but has hitherto proved elusive. In this work, a system is presented which shows significant promise in this respect. The isothermal cure of PLS nanocomposites based upon a tri‐functional epoxy resin (TGAP) has been studied by DSC, and displays two exothermic peaks. The first peak, very rapid, relates to a homopolymerization reaction within the intra‐gallery regions, while the second peak reflects the bulk crosslinking reaction. The occurrence of the intra‐gallery reaction before the bulk reaction enhances the degree of exfoliation in the cured nanocomposite. Furthermore, pre‐conditioning the resin/clay mixture before adding the curing agent and effecting the isothermal cure also allows a greater extent of intra‐gallery reaction to occur before the extra‐gallery epoxy‐amine reaction. Consequently, this system results in a high degree of exfoliation, as revealed by transmission electron microscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Studies on Cure Kinetics of Diglycidyl Ether of 4,4′-Bisphenol/4,4′-Diaminobiphenyl Using the Advanced Isoconversional Method

The cure kinetics of a rigid-rod epoxy monomer, diglycidyl ether of 4,4′-bisphenol (DGEBP), and the curing agent with the similar rigid-rod group, 4,4′-diaminebiphenyl (DABP), was studied using an advanced isoconversional method (AICM). DGEBP/DABP curing system was carried out by means of differential scanning calorimetry (DSC). Three exothermic peaks were depicted by nonisothermal DSC studies: the first two peaks were attributed to the curing reaction, and the last peak was attributed to the decomposition of the cured epoxy resin. The LC phase transformation of the curing process was observed by PLM. Using AICM, the largest activation energy of the curing reaction of DGEBP/DABP system was obtained as 108 kJ/mol. It can also be learned that LC phase transformation of the curing process affects the reaction significantly.     

Curing Characterization of the Bis-salicylaldehyde-triethylenetetramine Nickel (II)/Epoxy System

The curing reaction of epoxy resin and bis-salicylaldehyde-triethylenetetramine nickel (II) (Ni(sal)₂trien) was investigated using differential scanning calorimetry (DSC), UV-vis spectrometer and FT-IR. DSC measurement showed two distinct exothermic peaks on the curing curves, indicating that the reaction consisted of two reactive species. The first peak at low temperature corresponded to the amine-epoxy reaction with the activation energy of 46.85 kJ · mol^?1 and the second peak corresponded to the hydroxyl-epoxy reaction with the activation energy of 74.23 kJ · mol^?1. As the concentration of Ni(sal)₂trien increased, the amine–epoxy reaction was favored, and the temperature of the hydroxyl-epoxy reaction decreased at the same time.     

Comparative cure behavior of DGEBA and DGEBP with 4-nitro-1,2-phenylenediamine

Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and advanced isoconversional kinetic analysis were used to study the curing reaction of diglycidyl ether of 4,4′-bisphenol A (DGEBA) epoxy monomer with an aromatic amine, 4-nitro-1,2-phenylenediamine (4-NPDA). The first DSC exothermic peak was assigned to the curing process of DGEBA with 4-NPDA. Kinetic analysis suggested that the effective activation energy for the cure process decreases from ≈120 to a practically constant value ≈60 kJ mol⁻¹. This system was compared with diglycidyl ether of 4,4′-bisphenol (DGEBP)/4-NPDA. DGEBA/4-NPDA system shows higher reaction temperature, lower reaction rate and lower glass transition temperature under the same cure condition. This can be explained by stereochemical structure of epoxy monomer and the effect of conjugation.     

Effects of DICY content and metal oxide on the curing behavior of a brominated epoxy resin

The curing characteristics of a brominated epoxy resin/dicyandiamide (DICY) system in the presence of different DICY contents and metal oxides are studied using isothermal differential scanning calorimetry (DSC). From the exotherms obtained, it is found that the reaction heats increase with increasing DICY content and curing temperature because of greater amounts of DICY reacted. The amine–epoxy-related reaction dominates the major curing behavior and the T_g especially at the high curing temperature, while the etherification is more significant at low temperature and conversion and plays an important role in determining the rate of liquid-to-solid transition during the cure. The addition of metal oxides, Fe₂O₃, and ZnO, results in changes in the initial transition rate, T_g, activation energy, reaction heat, reaction rate, and reaction order. Three fillers respond differently because of a difference in the surface-activated reaction. Regardless of the complex curing mechanisms involved in the specimens, a simple kinetic expression can describe the curing extent at 180°C with good accuracy. © 1996 John Wiley & Sons, Inc.     

Preparation and properties of high performance phthalide‐containing bismaleimide modified epoxy matrices

A series of intercrosslinked networks formed by diglycidyl ether of bisphenol A epoxy resin (DGEBA) and novel bismaleimide containing phthalide cardo structure (BMIPP), with 4,4′‐diamino diphenyl sulfone (DDS) as hardener, have been investigated in detail. The curing behavior, thermal, mechanical and physical properties and compatibility of the blends were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), notched Izod impact test, scanning electron microscopy (SEM) and water absorption test. DSC investigations showed that the exothermic transition temperature (T_p) of the blend systems shifted slightly to the higher temperature with increasing BMIPP content and there appeared a shoulder on the high‐temperature side of the exothermic peak when BMIPP content was above 15 wt %. TGA and DMA results indicated that the introduction of BMIPP into epoxy resin improved the thermal stability and the storage modulus (G′) in the glassy region while glass transition temperature (T_g) decreased. Compared with the unmodified epoxy resin, there was a moderate increase in the fracture toughness for modified resins and the blend containing 5 wt % of BMIPP had the maximum of impact strength. SEM suggested the formation of homogeneous networks and rougher fracture surface with an increase in BMIPP content. In addition, the equilibrium water uptake of the modified resins was reduced as BMIPP content increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

用DSC研究选择聚丙烯腈原丝的共聚单体

本文主要利用差示扫描量热分析(DSC)研究了聚丙烯腈的共聚物及其原丝的热性能，研究结果发现国产原丝具有相似的放热单峰，而日本某公司的原丝具有两个峰，分峰使聚丙烯腈原丝放热峰宽化，避免了在预氧化、碳化时放热集中产生熔化、断丝现象．聚丙烯腈原丝的纺丝、溶解、氨改性等加工过程不能明显改变其放热峰的形状，而共聚单体的种类和组成配比才是最重要的因素，通过适当的共聚单体选择、配比设计可以制得具有与日本原丝放热峰相似的聚丙烯腈聚合物或原丝。     

Thermosetting cure diagrams: Calculation and application

The time–temperature–transformation (TTT) isothermal cure diagram and the continuous-heating-transformation (CHT) cure diagram are calculated from a reaction model for a high-T_g epoxy/amine system that has been developed to describe both epoxy/amine and etherification reactions in kinetically and diffusion-controlled reaction regimes. The cure diagrams are applied to various processing operations. The optimization of processing and of material properties by exploiting gelation and/or vitrification during cure is discussed. © 1994 John Wiley & Sons, Inc.     

The effect of kevlar fiber reinforcement on the curing,thermal, and dynamic‐mechanical properties of an epoxy/anhydride system

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.     

Etherification versus amine addition during epoxy resin/amine cure: An in situ study using near-infrared spectroscopy

The reactions between a multifunctional epoxy resin, tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) and a monofunctional amine, methylaniline (mAnil) are studied. Due to the existence of a tertiary amine catalytic center within the TGDDM molecule, the etherification reaction during cure of TGDDM is usually more significant than in other epoxide systems. The importance of this reaction relative to the amine addition reactions is investigated. In situ near-infrared spectroscopy is used to obtain kinetic data during the cure reactions. The reaction rate constants are calculated from linear regression analysis for both amine addition and etherification reactions based on the reaction mechanisms proposed. Arrhenius relationships are observed for all the reaction rate constants involved. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:895–901, 1998     

A logistic kinetic model for isothermal and nonisothermal cure reactions of thermosetting polymers

A model describing the low‐temperature crystallization kinetics observed for thermoplastic polymers from the melt by differential scanning calorimetry (DSC) was shown to accurately predict the cooling curves as a function of time and temperature. The model was successful for treating data for several cooling rates as well as for isothermal DSC data. In this article, we extended the model to cure reactions of thermosetting polymers. The parameters representing lower and upper exotherm reference temperatures in crystallization events have a different meaning for curing events. Thus, the model was modified to account for this change of context. The new model was tested for exothermic reactions of a Hysol® FP4527 epoxy adhesive system using data from DSC ramp heating experiments at several heating rates and also from isothermal experiments. Good fits were obtained for all the varied experimental conditions. The model made use of three fitting parameters with physical significance: a lower critical temperature (T_c) an activation energy (E_b), and a reaction order (τ + 1). Additionally, to complete the kinetic fitting, the dependence of the time to reach the reaction peak maximum for isothermal cure was considered. That dependence was found to follow a more simple model which is formally equivalent to that observed in isothermal crystallization, and which makes use of two parameters related to the limits of the temperature range in which the polymerization may occur. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40670.     

The effect of epoxy excess on the kinetics of an epoxy–anhydride system

The uncatalyzed cure of a commercial tetrafunctional epoxy monomer TGDDM (N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenylmethane) with hexahydrophthalic anhydride (HHPA), using variable stoichiometric ratios is reported. The reaction was followed by differential scanning calorimetry (DSC). Two kinds of experiments were performed: (1) fresh samples were run at several heating rates, and (2) samples, precured a certain time in an oil bath at constant temperature (i.e., 80 to 120°C), were run at 10°C/min. Two peaks were observed in the case of the epoxy excess but only one for the stoichiometric formulation: the peak at low temperature was attributed to the epoxy copolymerization with the anhydride while the peak at high temperature was attributed to the epoxy homopolymerization. The catalytic effect of the OH groups present in the epoxy monomer on the copolymerization reaction was demonstrated by the decrease in the activation energy of the propagation step when increasing the epoxy excess. There is a catalytic effect of the copolymerization product on the homopolymerization reaction. Our simplest model, proposed previously for a catalyzed epoxy/anhydride system [J. Polym. Sci. Part B: Polym. Phys. Ed., 37, 2799 (1999)], can be used to fit both isothermal and dynamical kinetic data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2342–2349, 2002     

Synthesis and properties of a novel bismaleimide resin containing 1,3,4‐oxadiazole moiety and the blend systems thereof with epoxy resin

A new bismaleimide monomer, 2‐((4‐maleimidophenoxy)methyl)‐5‐(4‐maleimidophenyl)‐1,3,4‐oxadiazole (Mioxd), was designed and synthesized. The chemical structure of the monomer was confirmed by means of Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹H NMR) spectroscopy and elemental analysis, and its thermal properties were characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Mioxd as a reactive modifier was blended with epoxy resin based on bisphenol A diglycidyl ether (DGEBA) in weight ratio of 5, 10, and 15%, using 4,4′‐diaminodiphenyl sulfone (DDS) as hardener. The effect of Mioxd addition on the cure behavior and thermal properties of the blend resins was studied by DSC, TGA, and dynamic mechanical analysis (DMA). DSC investigations showed that the main exothermic peak temperature (T_p) of the blend systems did not obviously shift with increasing Mioxd content whereas a new shoulder appeared and gradually grew on the high temperature side of the exothermic peak. The results of DMA measurements exhibited the glassy storage modulus (G') and glass transition temperatures (T_g) increased as the Mioxd content was increased, the cured blends investigated were miscible and no phase separation occurred. Further, the thermal decomposition temperature first decreased and then increased, but the char yield at 600°C increased with an increase in Mioxd content. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers