The quality of polymer composite materials depends on the distribution of the filler in the polymer matrix. Due to the presence of the oxygen functional groups, graphene oxide (GO) has a strong affinity to epoxy resins, providing potential opportunity for the uniform distribution of GO sheets in the matrix. Another advantage of GO over its nonoxidized counterpart is its ability to exfoliate to single-atomic-layer sheets in water and in some organic solvents. However, these advantages of GO have not yet been fully realized due to the lack of the methods efficiently introducing GO into the epoxy resin. Here we develop a novel homogeneous liquid phase transfer method that affords uniform distribution, and fully exfoliated condition of GO in the polymer matrix. The most pronounced alteration of properties of the cured composites is registered at the 0.10%-0.15% GO content. Addition of as little as 0.10% GO leads to the increase of the Young's modulus by 48%. Moreover, we demonstrate successful introduction of GO into the epoxy matrix containing an active diluent-modifier; this opens new venues for fabrication of improved GO-epoxy-modifier composites with a broad range of predesigned properties. The experiments done on reproducing the two literature methods, using alternative GO introduction techniques, lead to either decrease or insignificant increase of the Young's modulus of the resulting GO-epoxy composites.
Previously we have demonstrated that 4-quinolinecarboxylic acid amides and hydrazides, substituted at position 2, exhibit pronounced antiinflammatory and analgesic activity at a quite low toxicity [1 -5]. It was established that the charaeter and strength of the pharmacological action depend on the type of substituents at positions 2 and 4 of the quinoline cycle.As is known, introduction of the aroylpyruvoyl fragment into amides and hydrazides imparts to them a high antiinflammatory and analgesic activity [6,7]. In this connection, we have synthesized cinehoninie acid hydrazides containing aroylpyruvoyl fragments at the 15-nitrogen atom. The new compounds, namely, 13-aroylpyruvoyl hydrazides of 2-methyl-(I) and 2-phenyl-4-quinolinecarboxylic (II) acids were obtained using a reaction of 5-aryl-2,3-dihydro-2,3-furandiones with 2-methyl-and 2-phenyl-4-quinolinecarboxylic acids according to the scheme.Compounds I and II appear as white crystalline substances (except for Ih) poorly soluble in ethanol, benzene, chloroform, and acetonitrile, and soluble in DMSO and DMF. Their structures were established using the data of elemental analyses and the results of IR and IH NMR spectroscopic measurements. Similarly to the other pyruvic acid derivatives, the synthesized compounds provide red coloration of an ethanol solution of iron(Ill) chloride, which is evidence for the presence ofenolic hydroxyl [9,10].The IH NMR spectra of compounds Ia-Ih, IIb, and IIe contain signals attributed to the protons of methyl group (2.28-2.71 ppm), methoxy group (3.65-3.75ppm), and methine group (6.83-7.21 ppm), and a group of signals belonging to the protons of benzene ring and quinoline cycle I For the previous communication of this series see [1].
Mechanism and curing kinetics of bisphenol A epoxy resin-iso-methyltetrahydrophthalic anhydride compositions using quaternary phosphonium salts as accelerators were investigated by differential scanning calorimetry (DSC) and electrospray mass-spectrometry (ESI-MS). The DSC method was applied to investigate curing kinetics and apparent activation energy values for the overall curing process. The DSC results showed that some of the phosphonium salts lead to a lower activation energy, that means they are more effective accelerators for the curing of epoxy-anhydride systems. The mechanism of curing was studied by ESI-MS using the model reaction of epichlorohydrin (E) with phthalic anhydride (PA) in the presence of phosphonium salts or 2-methylimidazole. Products containing the alkyl moiety of the phosphonium salt in form of alkyl esters could be identified. This suggests that the phosphonium salts activate the anhydride by electrophilic attack.
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