Study of the epoxy system BADGE (n = 0)/1,2‐DCH/CaCO3 filler by DMA and DSC

The influence of an inorganic filler, CaCO₃, on the curing kinetics of an epoxy system composed of diglycidyl ether of bisphenol A [BADGE (n = 0)], 1,2‐diaminecyclohexane (1,2‐DCH), and CaCO₃ filler was studied by DMA and DSC. Different contents of filler in the range from 10 to 30%, referred to the total weight of the mixture, were tried. It was found that maximum reproducibility of the results and better performance correspond to a filler content of 20%. As usual, the T_g's obtained by DMA and DSC are different at 10–20°C. The results obtained from this study were compared with those corresponding to the system BADGE (n = 0)/1,2‐DCH without filler; the T_g for this last system is higher than that for the system with filler incorporated, whereas E′ and M_c (molecular weight between repetition units) are lower for the system without filler. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 366–370, 2002     

Lifetime predictions for the epoxy system BADGE n=0/m‐XDA using kinetic analysis of thermogravimetry curves

Lifetime of the epoxy system diglycidil ether of Bisphenol A (BADGE n=0)/ m‐xylylenediamine (m‐XDA) was calculated by thermogravimetric analysis. The Flynn‐Wall‐Ozawa method is used to determine the activation energy of the reaction. Experimental lifetimes in the range of 60–300°C vary from 1.41 10⁹ (2682 years) to 3.35 10^?4 min. This isoconversional method is not appropiate to calculate lifetime prediction because of high errors. Scaling factors were determined using the ratio of two reaction rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1692–1696, 2002     

Cationic polymerization behavior of β‐methylglycidyl ether derivatives and physical properties of their cationically cured materials

β‐Methylglycidyl ethers have been applied to Electrical and Electronic adhesives. However, there is no report about the detailed polymerization behavior and physical properties of their cured products. Hence, we investigated cationic polymerization behavior of bisphenol A di(β‐methylglycidyl) ether (Me‐BADGE) and physical properties of the cured products containing Me‐BADGE. DSC analysis suggested that Me‐BADGE could be cured completely at lower temperature than bisphenol A diglycidyl ether (BADGE). Physical properties were analyzed by dynamic viscoelastic analysis. Glass transition temperature (T_g) of BADGE homopolymer was 194°C. In contrast, the copolymer of BADGE (50 wt %) with Me‐BADGE (50 wt %) showed T_g at 124°C. According to the data of E’ and tan δ, crosslink density of the cured products decreased with increasing the Me‐BADGE content. The analysis of cationic polymerization of monofunctional β‐methylglycidyl ether suggested that the cationic polymerization proceeded not only through oxonium cation but also through carbocation formed by ring‐opening reaction of oxonium cation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42377.     

Effects of diffusion on the kinetic study of an epoxy system diglycidyl ether of bisphenol A/1,2‐diamine cyclohexane/calcium carbonate filler

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0), 1,2‐diamine cyclohexane (DCH) with calcium carbonate filler, were studied to determine different kinetic parameters. Two models—one based solely on chemical kinetics and the other accounting for diffusion—were used and compared to experimental data both for systems with and without filler. It was found that 100°C is the optimum service temperature, and also that the presence of the filler has no influence on the optimal service temperature range (60–100°C) of the epoxy system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2285–2295, 2000     

Effects of diffusion on the kinetic study of the system BADGE n = 0/m‐xylylenediamine

The curing reactions of an epoxy system composed of a diglycidyl ether of bisphenol A (BADGE n=0) and m‐xylylenediamine (m‐XDA) were studied. Two models, the first based solely on chemical kinetics and the second accounting for diffusion, were used and compared to the experimental data. The epoxy resin was used as received in a first series of experiments. In a second series of experiments, the resin was purified in vacuo (180°C and 1 mmHg). The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre‐ and postvitrification stages. The investigation was made in the temperature range 50–110°C, which is considered optimum for the isothermal curing of the epoxy system studied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2997–3005, 1999     

Activation energies for the epoxy system BADGE n = 0/m‐XDA obtained using data from thermogravimetric analysis

In this article we study the kinetics of thermal degradation of the epoxy system BADGE n = 0/m‐XDA using different kinetic methods with data from thermogravimetric analysis (TGA) in dynamic conditions. Activation energies obtained using different integral methods (Flynn‐Wall‐Ozawa and Coats‐Redfern Methods) are in good agreement with the value obtained using the Kissinger method (204.44 kJ/mol). The solid‐state decomposition mechanism followed by this epoxy system is a decelerated R_n type (phase boundary controlled reaction). We have also calculated activation energies using the Van Krevelen and the Horowitz‐Metzger methods. These last methods corroborate the decelerated behavior. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 776–782, 2001     

Effects of cure treatment on glass transition temperatures for a BADGE–DDM epoxy resin

The extent of cure for epoxy resin (BADGE) with a small excess of amine hardener (DDM, 4w/o) was determined by assay of the epoxy groups using near infrared spectroscopy. The effect of cure time at 100°C and postcure time at 180°C has been investigated. For the lower temperature cures the room temperature density, ρ_rt, increased with time, reaching a maximum at X_e = 0.37, and then decreased with extended cure times. For postcure, there was a monotonic decrease in ρ_rt that was unrelated to the extent of cure. There was an approximate linear relationship between glass transition temperature and In(t), which increased even when essentially all of the epoxy groups had reacted, that is X_e ∼ 0.99. © 1996 John Wiley & Sons, Inc.     

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO₂/MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H₂ concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H₂ concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H₂ reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H₂ concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H₂. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003     

Thermogravimetric study of degradation process of diglycidyl ether of bisphenol A–1,2‐diaminocyclohexane/calcium carbonate system

The thermal degradation of the epoxy system consisting of diglycidyl ether of bisphenol A (BADGE, n = 0)–1,2‐diaminocyclohexane (DCH) containing calcium carbonate filler is studied by thermogravimetric analysis to determine the reaction mechanism of the degradation process. The value of the activation energy, which is necessary for this study, is calculated using various integral and differential methods. The values obtained using the different methods are compared to the value obtained by Kissinger's method (234.84 ± 15.12 kJ/mol), which does not require knowledge of the n‐order value of the reaction mechanism. All the experimental results are compared to master curves in the range of Doyle's approximation (5–35% of conversion). The analysis of the results suggests that the reaction mechanism is a sigmoidal A₂ type. The thermodegradation mechanism is similar to that found for the same epoxy system without additives. However, for this last system the sigmoidal mechanism is an A₄ type. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1528–1535, 2002     

Synthesis and anticorrosion properties of poly(2,3‐dimethylaniline) doped with phosphoric acid

Poly(2,3‐dimethylaniline) (P(2,3‐DMA)) was synthesized chemically by using phosphoric acid (H₃PO₄) as protonic acid. The optimum ratio for n(H₃PO₄)/n(2,3‐DMA)/n(APS) was 2.5/1/2, and the optimum temperature was 30°C. The spectra of ultraviolet‐visible and infrared demonstrate that the structure of P(2,3‐DMA) was similar with polyaniline (PANI) except for the 2,3‐ortho‐substitute methyl. The result of X‐ray diffraction and solubility analysis indicate that owing to the 2,3‐ortho‐substitute benzene ring, the P(2,3‐DMA) has poorly partial crystallinity and better solubility. In addition, the anticorrosion property of P(2,3‐DMA) was better than PANI. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Curing behavior,thermal, and mechanical properties of epoxy resins cured with a novel liquid crystalline dicarboxylic acid curing agent

A novel di‐carboxylic acid curing agent (DACA) was successfully synthesized and cured with three different epoxy resins: glycidyl end‐capped poly(bisphenol‐A‐co‐epichlorohydrin) (pDGEBA, M_n = 377), N,N‐diglycidyl‐4‐glycidyloxyaniline (TGAP), and 4,4′‐methylenebis(N,N‐diglycidylaniline) (TGDDM). The cured epoxy exhibited excellent thermal stability, which was indicated by high initial degradation temperature (T_id) and char yield. The T_id values of cured epoxy were in the range of 327–338°C, and the char yields increased with increasing epoxy functionality. The char yields of cured DACA/pDGEPA, DACA/TGAP, and DACA/TGDDM samples were 21.1, 60.4, and 66.9%, respectively. In addition, the cured epoxy samples also showed low coefficients of thermal expansion and high storage moduli (E′), which were around 60 ppm/°C and 2800 MPa, respectively. The failure surfaces were ductile and rough, so the cured epoxy samples are expected to have high fracture toughness and impact strength. POLYM. ENG. SCI., 54:695–703, 2014. © 2013 Society of Plastics Engineers     

UV–Vis observation of different F0 → D0 transitions for both isomeric species in Eu(III) DOTA-like complexes

The presence of the two isomeric species (M and m) of Eu(III) (DOTA-like) complexes has been detected in aqueous solution by UV–Vis absorbance spectrophotometry. It shows that the ⁷F₀ → ⁵D₀ transition in Eu(III) complexes does not only depend on the coordinating atoms present in the first coordination sphere but that it may also be influenced by small differences in the coordination geometry. The absorbance spectra could be well fitted with the K=M/m equilibrium constants measured by NMR. The wavelength variation between the two isomers is found to be 0.20 nm (DTMA), 0.14 nm (DOTA) and about 0.25 nm (DOTAM) (DTMA=1,4,7,10-tetrakis-(methylcarbamoylmethyl)-1,4,7,10-tetraazacyclo-dodecane; DOTA=1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)-cyclododecane; DOTAM=1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane). This is small enough not to affect the quantitative determination of water coordination equilibria in solution as hydration equilibria produce differences of about 0.5 nm.     

Kinetic analysis of relaxation process for the epoxy network diglycidyl ether of bisphenol A/m‐xylylenediamine

The relaxation kinetic of the epoxy network diglycidyl ether of bisphenol A (BADGE n = 0) and m‐xylylenediamine (m‐XDA) was analyzed from DSC experimental data, using different theoretical models. Based on a Petrie model, which involved separate contributions of temperature and structure, three characteristic parameters were calculated: a preexponential factor A, an apparent activation energy E_H, and a parameter C, which indicate the dependency of relaxation time on structure. This model allowed us to calculate the relaxation function at different ageing temperatures. Another method used to study a relaxation kinetic was the Kovacs–Hutchinson model, which takes into account the dependency of the relaxation time on temperature and structure. The last model used was a two‐parameter equation from Williams–Watts, where the relaxation time is independent of temperature. Using data of characteristic times a master curve for the relaxation function was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1591–1595, 2005     

Kinetic and thermodynamic studies of an epoxy system diglycidyl ether of bisphenol A/1, 2 diamine cyclohexane/calcium carbonate filler

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0) and 1,2‐diaminecyclohexane (DCH) with a calcium carbonate filler was studied by differential scanning calorimetry (DSC) and using a scanning electronic microscope (SEM). As a first stage, the optimum content of the filler determined was 20%. From a kinetic study, in which two models were used, parameters such as reaction orders, rate constants, and activation energies were determined. A thermodynamic study allowed calculation of enthalpy (ΔH^#), entropy (ΔS^#), and free‐energy ((ΔG^#) changes. The results were compared to those obtained for the same epoxy systems without the filler. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 291–305, 2000     

Fatigue behavior of filament‐wound glass fiber reinforced epoxy composite tubes under tension/torsion biaxial loading

A study of filament‐wound glass fiber/epoxy composite tubes under biaxial fatigue loading is presented. The focus is placed on fatigue lives of tubular specimens under tension/torsion biaxial loading at low cycle up to 100,000 cycles. Filament‐wound glass‐fiber/epoxy tubular specimens with three different lay‐up configurations, namely [±35°]_n, [±55°]_n, and [±70°]_n lay‐ups, are subjected to in‐phase proportional biaxial cyclic loading conditions. The effects of winding angle and biaxiality ratio on the multiaxial fatigue performance of composites are discussed. Specimens are also tested under two cyclic stress ratio: R = 0 and R = −1. The experimental results reveal that both tensile and compressive loading have an influence on the multiaxial fatigue strength, especially for [±35°]_n specimens. A damage model proposed in the literature is applied to predict multiaxial fatigue life of filament‐wound composites and the predictions are compared with the experimental results. It is shown that the model is unsuitable for describing the multiaxial fatigue life under different cyclic stress ratios. POLYM. COMPOS. 28:116–123, 2007. © 2007 Society of Plastics Engineers     

A novel reaction of epoxy resins with polyfunctional active esters

Addition reactions of commercial epoxy resins such as bisphenol-A diglycidylether (BADGE), ethylene glycol diglycidylether (EGGE), and N,N-diglycidylaniline (GAN) with various active esters such as di[S-(benzothizolyl)] thioadipate (BTAD), di(4-nitrophenyl) adipate (NPAD), di(S-phenyl) thioadipate (PTAD), and 4-nitrobenzoyl esters of polyfunctional phenols were carried out in neat using quaternary salts or crown ether-salts complexes as a catalyst at 50–130°C. The rate of addition reaction of BTAD was faster than that with other esters under the same reaction conditions. Furthermore, it was found that the rate of addition reaction of the epoxy resins with some active esters was strongly affected by the kind of epoxy resin, the structural formula of carboxylic acid, and the kind of catalyst. The reaction of epoxy resins with polyfunctional active esters proceeded quantitatively at the elevated temperatures. However, some of the mixtures of epoxy resin, polyfunctional active ester and the catalyst showed excellent storage stability at 30°C.     

Extractive Separation of Lithium Isotopes by Crown Ethers

Abstract

Separative abilities of crown ethers to lithium isotopes were investigated for the number of oxygen atoms composing crown rings and for the substituted groups to 15-crown-5. The separation factors at 0°C were 1.057 for 12-crown-4, 1.042 for benzo-15-crown-5, 1.041 for lauryloxymethyl-15-crown-5, 1.043 for tolyloxymethyl-15-crown-5, and 1.024 for dicyclohexano-18-crown-6. The enthalpy change of the isotopic equilibrium in the absolute value was the greatest for 12-crown-4; ΔH° = ?0.78 kJ/mol. In the substituted 15-crown-5s the separation factor was greatest for tolyloxymethyl-15-crown-5, and ΔH° values decreased in the order: benzo- > tolyloxymethyl- > lauryloxymethyl-15-crown-5. For enthalpy changes, benzo-15-crown-5 has the possibility of giving a larger separation factor than the present one, α = 1.042, by choosing more suitable conditions. In spite of its large distribution coefficient, dicyclohexano-18-crown-6 is not superior for isotopic separation of lithium in regard to the small enthalpy change of isotopic equilibrium; ΔH° = ?0.15 kJ/mol. The addition of DMSO to the initial solution of LiI caused a remarkable increase in the distribution coefficient without changing the isotopic separation factors.     

Study of the physical aging of the epoxy system BADGE n = 0/m‐XDA/CaCO3

The physical aging of the epoxy network consisting of a diglycidyl ether of bisphenol A (BADGE n = 0), m‐xylylenediamine (m‐XDA), and calcium carbonate was studied by differential scanning calorimetry. The glass transition temperature and the variation of the specific heat capacities were calculated using the method based on the intersection of both enthalpy–temperature lines for glassy and liquid states. The apparent activation energy was calculated using a single method that involved separate temperature and excess enthalpy dependency. All calorimetric data were compared with those obtained for the epoxy network without filled calcium carbonate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure–Activity Relationship Studies of Amino Acid Substitutions in Radiolabeled Neurotensin Conjugates

Radiolabeled derivatives of the peptide neurotensin (NT) and its binding sequence NT(8–13) have been studied as potential imaging probes and therapeutics for NT‐1‐receptor‐positive cancer. However, a direct comparison of reported NT analogues, even if radiolabeled with the same radionuclide, is difficult because different techniques and models have been used for preclinical evaluations. In an effort to identify a suitable derivative of NT(8–13) for radiotracer development, we herein report a side‐by‐side in vitro comparison of radiometallated NT derivatives bearing some of the most commonly reported amino acid substitutions in their sequence. Performed investigations include cell internalization experiments, determinations of receptor affinity, measurements of the distribution coefficient, and blood serum stability studies. Of the [¹⁷⁷Lu]‐1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA)‐labeled examples studied, analogues of NT(8–13) containing a short hydrophilic tetraethylene glycol (PEG₄) spacer between the peptide and the radiometal complex, and a minimum number of substitutions of amino acid residues, exhibited the most promising properties in vitro.     

Chemical modification of chitosan: Synthesis and characterization of chitosan‐crown ethers

Four novel Schiff‐type chitosan (CTS)‐crown ethers were synthesized through a reaction between ? NH₂ in CTS or crosslinked chitosan (CCTS) and ? CHO in 4′‐formylbenzo‐crown ethers, and four secondary‐amino‐type CTS‐crown ethers were prepared through the reduced reaction of NaBH₄, respectively. Their structures were characterized by elemental analysis, Fourier transform infrared (FTIR) spectra analysis, solid‐state ¹³C‐NMR analysis, and X‐ray diffraction (XRD) analysis. The elemental analysis results showed that the percentage of nitrogen in all CTS‐crown ethers were lower than that of CTS or CCTS. From the FTIR data of CTS, CCTS, and CTS‐crown ethers I–VIII, we saw that the characteristic peaks of C?N, N? H, and Ar appeared and that the characteristic peaks of pyranoside in the chain of CTS or CCTS were not destroyed. The XRD spectra demonstrated that CTS‐crown ethers I–VIII gave lower crystallinities than CTS or CCTS, which indicated that these compounds were considerably more amorphous than CTS or CCTS. In the solid‐state ¹³C‐NMR spectra, all of these CTS‐crown ethers had a particular peak of aromatic at 128 or 129 ppm, and the greatest difference between Schiff‐type CTS‐crown ethers and secondary‐amino‐type CTS‐crown ethers was that the Schiff‐type CTS‐crown ethers had the particular peak of C?N, which disappeared in secondary‐type CTS‐crown ethers. All these facts confirmed that the structures of CTS‐crown ethers I–VIII were as expected. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2221–2225, 2003