The glass transition temperature,Tg is a sensitive and practical parameter for following cure of reactive thermosetting systems. A new equation was developed for predicting theTg-conversion relationship based on the Dillman-Seferis viscoelastic compliance model. It assumes that the changes inTg are primarily due to changes in relaxation time as chain extension and crosslinking reduce the mobility of a polymer network. Such information is essential in combining kinetic and viscoelastic measurements, which monitor transformations of thermosets during cure. The equation derived from the viscoelastic model was shown to be applicable for a variety of experimental data. The success of the methodology was further demonstrated by comparing well-established relations, such as the Fox equation and the Di-Benedetto equation, to predictions made possible by adjusting two viscoelastic model parameters. Finally, the fitting power of the proposed equation was shown by fitting published epoxy data from the literature as well as experimental data on a relatively new resin system such as dicyanates used as a model in this study.
The hydrogen-isotope exchange reaction (T-for-H exchange reaction) between each solid material having two different kinds of functional groups and HTO vapor has been observed at several temperatures. Solid materials used were monosubstituted aminobenzenes. The rate constant (k) for each functional group was obtained by applying both the A"-McKay plot and the date obtained. Comparing these k values quantitatively leads to the followings: (1) the A"-McKay plot is useful in obtaining the reactivity of the compounds having two different kinds of functional groups; (2) as to m-aminobenzenesulfonic acid, the reactivity of the SO3H group is about 6.6-8 times larger than that of the NH2 group, and the temperature dependence of the reactivity of the SO3H group is also larger than the dependence of that of the NH2 one; (3) the reactivity of the NH2 group of some kinds of monosubstituted aminobenzenes may follow the Hammett rule; (4) the substituent constant (s) of SO3H group is estimated as follows: sm is 0.38, and sp is 0.64; (5) the substituent-effect of SO3H group is generally larger than that of other substituents; and (6) the subsutituent-effect unknown can be estimated by applying both the Hammett rule and A"-McKay plot.
The formation of benzynes derivatives from ortho-trimethylsilyl triflates using tetra-n-butylammonium fluoride (TBAF) as the benzyne-forming trigger was achieved in a straightforward flow reactor at room temperature. These benzynes were immediately trapped in Diels—Alder reactions to deliver the desired cycloadducts.
Authors:Robert Ianoş, Ioan Lazău, and Cornelia Păcurariu
The reactivity of LiNO3 and Al(NO3)3 with respect to urea and β-alanine was investigated. Experimental results proved that β-alanine is a more suitable fuel for
LiNO3, whereas urea seems to be more adequate for Al(NO3)3. Based on the different metal nitrate/fuel mixture reactivity, nanocrystalline γ-LiAlO2 powders were prepared by solution combustion synthesis using a fuel mixture of urea and β-alanine. This fuel mixture yielded
single-phase nanocrystalline γ-LiAlO2 (32.6 nm) directly from the combustion reaction. The resulted powder had a specific surface area of 3.2 m2/g and no supplementary annealing was required. On the other hand, pure γ-LiAlO2 could not be obtained by using a single fuel (urea, β-alanine) unless annealing at 900 °C for 1 h was performed.
Authors:Celestyna Mila-Kierzenkowska, Alina Woźniak, B. Woźniak, G. Drewa, Bogumiła Chęsy, T. Drewa, Ewa Krzyżyńska-Malinowska, and R. Ceraficki
In this study we examined superoxide dismutase (SOD) activity and thiobarbituric acid reactive substances (TBARS) concentration in liver and muscles of four fish species: the carp, the brown trout, the white cod and the flounder. Higher SOD activity and higher TBARS concentration was revealed in the tissues of marine fish in comparison to freshwater fish. The highest SOD activity was observed in the cod while the highest TBARS concentration was in the flounder. The observed differences are probably an effect of the different living mode of the compared fish.
Authors:M. Villanueva, I. Fraga, J. Rodríguez-Añón, and J. Proupín-Castiñeiras
The rheological behaviour of the materials diglycidil ether of bisphenol A (n = 0), 1, 2 diamine-cyclohexane and the epoxy reactive diluent vinylcyclohexane dioxide have been studied both separately
and mixed before the beginning of the curing reaction. Different kinds of tests such as: preshear and time sweep, flow curve
and stress sweep experiments were carried out. From these experiments, interesting information about: viscosity-shear stress
and viscosity-shear rate dependences, storage modulus and the linear viscoelastic region were found out. Relationships between
concentration of diluent and the final viscosity of the mixed sample and also between percentage of diluent and storage modulus
The effect of dissociation on the reactivity and inhibition capacity of p-nitro-phenol /p-NPH/ towards orthopositronium atom has been investigated by performing positron lifetime measurements in methanol and methanol containing 0.5M NaOH solutions, respectively. In the latter case the solute exists in anionic form /p-NP–/. It has been found that as a result of dissociation, both the rate constant /k/ and the inhibition coefficient // decrease significantly. Their values are k=/7.5±0.4/×108 s–1 M–1 and =6.8±0.2 M–1 for p-NPH and kd=/0.6±0.2/×108 s–1 M–1 and
d=4.0±0.2 M–1 for p-NP–. The possible reasons for these effects are discussed.
The present study deals with the radiolysis of tetracycline hydrochloride dissolved in aerated alkaline aqueous solutions containing 0.1, 0.5 and 1M NaOH, at 77 K, as followed by ESR. The rate constants for the reactions between the electron and physical and chemical traps which are present in these solutions are calculated. These values are kph= =9.6·1015 l·mol–1·s–1 and kch=1.3·1010 l·mol–1·s–1. The reactivity of electrons that are formed in the radiolysis of water decreases in the following proportions: physical traps: chemical traps: molecules of water: 4.8·1014: 6.5·108: 1.0. The electrons react preferentially with the solute instead of the solvent.