Anhydride System Research Articles

Input Multiplicity Analysis in a Non‐Isothermal CSTR for Acid‐Catalyzed Hydrolysis of Acetic Anhydride

AbstractMultiplicity analysis gives practical guidance for process design to eliminate difficult operating regions associated with input and output multiplicities. Continuous stirred tank reactors (CSTRs) present challenging operational problems due to complex behavior such as input and output multiplicities, ignition/extinction, parametric sensitivity, and nonlinear oscillations. In the absence of a unified mathematical theory for representing various nonlinear system characteristics, the present study was aimed at understanding the dynamic behavior of CSTRs by means of experiments and to link the experimental data to theoretical considerations for further detection and elimination of operating problems. Theoretical modeling and analysis of a non‐isothermal CSTR with acid‐catalyzed hydrolysis of an acetic anhydride system for input multiplicity are discussed. Theoretical modeling of a non‐isothermal CSTR using a root‐finding technique was carried out for predicting steady‐state temperatures. Alternatively, a mathematical model for a non‐isothermal CSTR using unsteady‐state mass and energy balance equations is proposed. Computer‐based simulation was carried out using a program developed in MATLAB for final transient temperature and time‐temperature data of the CSTR system under investigation. The results of a theoretical analysis conducted for confirming the existence of input multiplicity in non‐isothermal CSTRs with acid‐catalyzed hydrolysis of acetic anhydride were compared with experimental investigations for validation.

Synthesis of Liquid Crystalline Epoxy Resin p-BDEPB and Cure Kinetics with 3-MeTHPA

A liquid crystalline epoxy resin of p-biphenylene di-4-(2,3-epoxypropyloxy)benzoate (p-BDEPB) was synthesized from allyl bromide, 4-hydroxy ethyl benzoate and 4,4-dihydroxybiphenyl. Its structure and liquid crystalline behavior were characterized by DSC, 1H-NMR, FTIR, POM and XRD. The results are shown that this compound is smectic liquid crystalline.The melting point of p-BDEPB is 210 oC and clearing point is over 300 oC, the epoxy value is 0.312 mol/100g. The average curing Ea of p-BDEPB/3-methyl-tetrahydrophthalic anhydride (MeTHPA) system is 97.2kJ/mol. The gel point of cured-system Tgel is 89.0 oC, curing temperature Tcu is 132.5 oC and finishing temperature Tf is 146.5 oC. The curing reaction can be described by the autocatalytic Šesták-Berggren (S-B) equation, the two reaction orders m and n is 0.23 and 0.74, respectively.

Effect of polysulfide modifier on mechanical and morphological properties of epoxy/phthalic anhydride system

Blend samples were prepared by physical mixing of epoxy resin with varying concentration of liquid polysulfide. The blend samples were cured with aromatic acid anhydride. A comparative study of Fourier transform infrared spectra (FTIR) showed the modification as a result of chemical reaction between epoxide group, curing agent and polysulfide. The tensile strength of cured samples decreased slightly, whereas the elongation at break showed an increasing trend with increase in polysulfide content i.e. up to 50 gm. phr, in the blend samples. Appreciable improvements in impact strength were also observed in the prepared blend systems. The cured resin blend showed two phase morphology where the rubber domains were dispersed in the epoxy matrix.

Morphology and thermal and dielectric behavior of cycloaliphatic epoxy/trimethacrylate interpenetrating polymer networks for vacuum‐pressure‐impregnation electrical insulation

AbstractVacuum pressure impregnation has been known as the most advanced impregnation technology that has ever been developed for large and medium high‐voltage electric machines and apparatuses. We developed one new type of vacuum‐pressure‐impregnation resin with excellent properties by means of a novel approach based on in situ sequential interpenetrating polymer networks resulting from the curing of trimethacrylate monomer [trimethylol‐1,1,1‐propane trimethacrylate (TMPTMA)] and cycloaliphatic epoxy resin (CER). In this study, the influence of the concentrations of the components and their microstructures on their thermal and dielectric behaviors were investigated for the cured CER/TMPTMA systems via atomic force microscopy, dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis. The investigation results show that the addition of TMPTMA to the CER–anhydride system resulted in the formation of a uniform and compact microstructure in the cured epoxy system. This led the cured CER/TMPTMA systems to show much higher moduli in comparison with the pure CER–anhydride system. The thermogravimetric analysis results show that there existed a decreasing tendency in the maximum thermal decomposition rates of the cured CER/TMPTMA systems, which implies that the thermal stability properties improved to some extent. The dielectric analysis results show that the cured CER/TMPTMA systems displayed quite different dielectric behaviors in the wide frequency range 0.01 Hz–1 MHz and in the wide temperature range 27–250°C compared with the cured CER–anhydride system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

2H‐Pyrrole Derivatives from an Aza‐Nazarov Reaction Cascade Involving Indole as the Neutral Leaving Group

AbstractTrifluoromethyl‐substituted N‐indolinyl‐1‐aza‐1,4‐dien‐3‐ones 4, which are accessible in good yields from indolinylimino esters 6 in a two‐step procedure, undergo a novel type of aza‐Nazarov cyclization if treated with strong acids to give the hitherto unknown 3‐hydroxy‐5H‐pyrrole derivatives 8a–p. The solvent‐free polyphosphoric acid/acyl anhydride system as the acidic reaction medium is especially efficient and requires only short reaction times. According to quantum chemical calculations the key step in the reaction cascade is the cleavage of the N–N bond of the hydrazone fragment of a protonated N‐(indolin‐1‐yl)‐1‐aza‐1,4‐dien‐3‐one intermediate such as 10. This intermediate releases 3H‐indole as an unusual, but very efficient neutral leaving group. Several 1‐aza‐1,4‐dien‐3‐ones 4 and some 3‐hydroxy‐5H‐pyrrole derivatives 8 were characterized by X‐ray diffraction.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis and Glycosylation of a Series of 6-Mono-, Di-, and Trifluoro S-Phenyl 2,3,4-Tri-O-benzyl-thiorhamnopyranosides. Effect of the Fluorine Substituents on Glycosylation Stereoselectivity

A series of 6-mono-, di-, and trifluoro analogs of S-phenyl 2,3,4-tri-O-benzyl-D- or L-thiorhamnopyranoside has been synthesized and used as donors in glycosylation reactions, with activation by the 1-benzenesulfinyl piperidine/triflic anhydride system. The stereochemical outcome of the glycosylation reactions was found to depend on the electron-withdrawing capability of the disarming substituent at the 6-position, i.e., on the number of fluorine atoms present. The results are explained with regard to the increased stability of the glycosyl triflates, shown to be intermediates in the reaction by low-temperature 1H NMR experiments, with increased fluorine content.

The kinetic study of the curing reaction of mono- and di-epoxides obtained during the reaction of divinylbenzene and hydrogen peroxide with acid anhydrides

In this paper, the non-isothermal differential scanning calorimetry (DSC) was employed to investigate the cure process and to determine the kinetic parameters of the curing reactions of mono- and di-epoxides with maleic and glutaric anhydrides. The epoxides were obtained during the epoxidation process of commercially available divinylbenzene by using 60% hydrogen peroxide as the oxidant in the presence of organic solvents and magnesium oxide as the catalyst. It was found that the cure process of epoxides with maleic anhydride was described through higher values of enthalpy of polymerization (Δ H R) and lower temperatures of the cure initiation ( T onset), the peak maximum temperature ( T max) and the final cure temperature ( T end). It can be considered to accelerate the rate of reaction and lead to an excellent network structure when maleic anhydride was used as curing agent. The kinetic analysis was firstly computed using a model free-estimation of the activation energy (Friedman, Ozawa–Flynn–Wall methods) and then the multivariate non-linear regression with a 6th degree Runge–Kutta process in a modified Marquardt procedure was employed to calculate the corresponding kinetic parameters ( E i , n i , A i ) using the nth-order reaction f( α). The unbranched three-step process of the nth-order reaction f( α) for each step was the best to describe the cure process of mono- and di-epoxide with acid anhydrides. The determined values of the activation energies were in the range 64.7–105.2 kJ/mol for epoxides/glutaric anhydride system and 64.7–82.7 kJ/mol when maleic anhydride was used as hardening agent.

Use of Fourier Transform Infrared Spectroscopy to Follow the Heterocumulene Aided Thermal Dehydration of Phthalic and Naphthalic Acids

Fourier transform infrared (FT-IR) spectroscopy has been successfully employed to follow the formation of phthalic anhydride and 1,8-naphthalic anhydride on heating their corresponding acids. The effects of three heterocumulenes, cyanamide, dicyandiamide, and sodium cyanate, on the temperature of formation of the anhydrides were also investigated using this method. It was found that the carbodiimides cyanamide and dicyandiamide dramatically lowered the temperature at which thermal dehydration of the acid led to anhydride formation. It was noted that cyanamide had a stronger catalytic effect than dicyandiamide, presumably due to the electron-withdrawing effect of the amidine group. Sodium cyanate was also found to promote the thermal dehydration of the acids to form the corresponding anhydrides. Under more severe conditions, phthalic acid anhydride formed is seen to react further, leading to the formation of phthalimide. The discrepancy between the products obtained with cyanamide and sodium cyanate leads to the conclusion that, unlike earlier claims, imide formation is not due to the reaction of the anhydride with the urea formed but with sodium cyanate itself. However, only the phthalic anhydride five-membered ring system is sufficiently reactive towards the CNO- nucleophile to form the imide; the six-membered 1,8-naphthalic anhydride system does not react in this way.

Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system

Curing kinetics and mechanism of liquid lignin based epoxy resin (LEPL)–maleic anhydride (MA) system accelerated with benzyldimethylamine (BDMA) were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). In order to investigate the difference in the curing process, heating FTIR was used to study the change of the functional group. Complete consumption of the epoxides has been observed after the heating temperature was higher than 110°C. E constant method and E variable method, to study the dynamic DSC curves, were deduced by assuming a constant and a variable activation energy, respectively. With E constant method, the cure reaction activation energy E, the frequency factor A and overall order of reaction n+m are calculated to be 59.68kJmol−1, e20.6 and 1.462, respectively. With E variable method, E is proved to decrease initially, and then increases as the cure reaction proceeds. The value of E spans from 60.16 to 87.80kJmol−1. With the E constant method, E variable method and heating FTIR spectra used together, we can have a comprehensive and profound understanding of the cure reactions of the LEPL–MA system.

Curing Kinetics of o-Cresol Formaldehyde Epoxy Resin and Succinic Anhydride System Catalyzed by Tertiary Amine

The kinetics of the cure reaction for system of o-cresol formaldehyde epoxy resin (o-CFER)/succinic anhydride (SA) and tertiary amine as a catalyst was investigated with a differential scanning calorimeter (DSC). Autocatalytic behavior was shown in the first stages of the cure for the system, which was well described by the model proposed by Kamal that includes two rate constants, k1 and k2, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2.1-2.6, and the activation energy for k1 and k2 was 109 and 72.0 kJ/mol, respectively. In the later stages, a cross-linked network was formed and the cure reaction is mainly controlled by diffusion. Diffusion factor, f(alpha), was introduced into Kamal's equation, then the calculated values agree very well with the experimental data. The molecular mechanism of this curing reaction was discussed.

Further investigation of polyaminoamide‐epichlorohydrin/stearic anhydride compatibilizer system for wood‐polyethylene composites

AbstractThe combination of a polyaminoamide‐epichlorohydrin (PAE) resin (a paper wet strength agent) and stearic anhydride was recently reported as an effective compatibilizer system for wood‐polyethylene composites. Further investigation of this new compatibilizer system revealed that the pH value of a PAE solution, dosages of PAE and stearic anhydride, and the weight ratio of PAE to stearic anhydride had significant impacts on the compatibilization effects of the compatibilizer system. Adjusting the pH value of the PAE solution from 5.0 to 10.4 increased the strength of the resulting wood‐polyethylene composites. The highest strength of the resulting wood‐polyethylene composites was obtained at 3 wt % PAE and 3 wt % stearic anhydride. At 4 wt % or 6 wt % of a compatibilizer, this PAE‐stearic anhydride system was superior to maleic anhydride‐grafted polyethylene (MAPE), one of the most effective compatibilizers, in terms of enhancing the strength of the resulting wood‐polyethylene composites. Fourier transform infrared spectroscopy (FTIR) analysis revealed that PAE and stearic anhydride formed covalent bonding with wood flour. The compatibilization mechanisms of this PAE‐stearic anhydride compatibilizer system were investigated in detail. Water‐resistance tests indicated that the PAE‐stearic anhydride compatibilizer system increased the water‐resistance of the resulting composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 712–718, 2006

Phosphoric Acid-Promoted Synthesis of 4-Acylpyrrole-2-carboxylic Esters and Dipyrryl Ketones from Mixed Anhydrides

[reaction: see text] An efficient synthesis of 4-acylpyrrole-2-carboxylic esters utilizing a phosphoric acid-catalyzed mixed anhydride system is described. The new route also enables the preparation of dipyrryl ketones and N-confused dipyrryl ketones.

A combination of poly(diphenylmethane diisocyanate) and stearic anhydride as a novel compatibilizer for wood–polyethylene composites

A combination of poly(diphenylmethane diisocyanate) (PMDI) and stearic anhydride was investigated as a new compatibilizer system for improving the interfacial adhesion between wood and polyethylene (PE). The treatment of wood flour with PMDI increased both the modulus-of-rupture (MOR) and the modulus-of-elasticity (MOE) of the resulting wood–PE composites. The combination of stearic anhydride and PMDI further increased both MOR and MOE of the resulting composites. Compared with the commercially used compatibilizer maleic-anhydride-grafted polyethylene (MAPE), the PMDI-stearic anhydride compatibilizer system resulted in significantly higher MOR and MOE. The moisture content of wood flour affected the compatibilization of both the PMDI-stearic anhydride compatibilizer system and MAPE. The compatibilization mechanisms of PMDI-stearic anhydride system were investigated in detail. Water-resistance tests indicated that the composites with the PMDI-stearic anhydride system were statistically more water-resistant than those with MAPE.

Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo-montmorillonite (O-MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The dispersion state of the MMT in the matrix was investigated by X-ray diffraction and scanning electronic microscopy. The thermal stability of the epoxy nanocomposites was examined by TGA. Thermal stability of the epoxy nanocomposite is dependent upon the dispersion state of the OMMT in the epoxy matrix although all the epoxy nanocomposites had enhanced thermal stability compared with the neat epoxy resin. The thermal stability of the epoxy resin nanocomposites was correlated with the dispersion state of the MMT in the epoxy resin matrix.

Exploitation of introducing of catalytic centers into layer galleries of layered silicates and related epoxy nanocomposites. I. Epoxy nanocomposites derived from montmorillonite modified with catalytic surfactant‐bearing carboxyl groups

AbstractMontmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo‐montmorillonite (O‐MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X‐ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O‐MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O‐MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass‐transition temperatures (Tg's) of the exfoliated nanocomposite were 20 °C higher than that of the neat resin. At higher O‐MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher Tg's as compared with the neat resin. O‐MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O‐MMT loading. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1192–1198, 2004

Use of temperature‐modulated DSC in kinetic analysis of a catalysed epoxy–anhydride system

AbstractThe curing kinetics of a catalysed epoxy‐anhydride system was studied by temperature‐modulated differential scanning calorimetry. The chemical‐controlled regime was analysed by empirical kinetic equations. The diffusion‐controlled regime was detected by the diffusion factor, DF(α,T), which was calculated from the ratio of the experimental rate to the chemical reaction rate. DF(α,T) was compared with a mobility factor, MF(α,T), which was obtained by measuring the modulus of the complex heat capacity |Cp*|. The equivalence of the two factors allowed the diffusion‐controlled regime to be studied using the |Cp*| signal. However, the results obtained in the epoxy–anhydride system showed a limitation to the method, and this is discussed in terms of the modulation period necessary for the variation in MF(α,T) to occur in the same conversion interval as does DF(α,T). Copyright © 2004 Society of Chemical Industry

Electrically conductive composites based on epoxy resin containing polyaniline–DBSA‐ and polyaniline–DBSA‐coated glass fibers

AbstractFour kinds of polyaniline (PANI)‐coated glass fibers (GF–PANI) combined with bulk PANI particles were synthesized. GF–PANI fillers containing different PANI contents were incorporated into an epoxy–anhydride system. The best conductivity behavior of the epoxy/GF–PANI composites was obtained with a GF–PANI filler containing 80% PANI. Such a composite shows the lowest percolation threshold at about 20% GF–PANI or 16% PANI (glass fiber‐free basis). The PANI‐coated glass fibers act as conductive bridges, interconnecting PANI particles in the epoxy matrix, thus contributing to the improvement of the conductivity of the composite and the lower percolation threshold, compared with that of a epoxy/PANI–powder composite. Particularly, the presence of glass fibers significantly improves the mechanical properties, for example, the modulus and strength of the conductive epoxy composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1329–1334, 2004

Processing and characterization of epoxy–anhydride‐based intercalated nanocomposites

AbstractA study of the kinetic and thermal characterization of an epoxy resin (DGEBA) polymerized with a methyl tetrahydrophthalic anhydride reinforced with montmorillonite‐layered silicates is presented. The nanoreinforcement used was compatibilized by exchanging the cations between the silicate layers with alkylammonium salts, containing long hydrocarbon chains. The aim of this study was to develop new nanocomposites based on thermoset resins with improved thermal stability, suitable for electronic applications. Differential scanning calorimetry was used here to produce the polymerization kinetics data, while thermogravimetric analysis was used to evaluate the effects of the nanoreinforcements on the thermal stability and to analyze the degradation kinetics. Unexpected strong effects of the nanocomposite on the polymerization kinetics of the epoxy–anhydride system were detected and evaluated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2532–2539, 2003

Curing kinetics and thermal property characterization of the bisphenol‐F epoxy resin and phthalic anhydride system

AbstractThe curing kinetics of bisphenol‐F epoxy resin (BPFER) and curing agent phthalic anhydride, with N,N‐dimethylbenzylamine as an accelerator, were studied by differential scanning calorimetry (DSC). Analysis of DSC data indicated autocatalytic behaviour in the first stages of the cure for the system, and that this, could be well described by the model proposed by Kamal, which includes two rate constants, k1 and k2, and two reaction orders, m and n. The curing reaction in the later stages was practically diffusion‐controlled. To consider the diffusion effect more precisely, a diffusion factor, 𝒻(α), was introduced into Kamal's equation. The glass transition temperatures (Tgs) of the BPFER/phthalic anhydride samples were determined by means of torsional braid analysis. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis.© 2002 Society of Chemical Industry

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

AbstractThe 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