Cu(acac)<Subscript>2</Subscript>–PVA composite nanofibers in catalysis of Michael addition of carbon nucleophiles to α,β-unsaturated carbonyl compounds

Copper (II) acetylacetonate containing nanofibers of polyvinyl alcohol (Cu(acac)₂–PVA) were prepared by electrospinning and characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, inductively coupled plasma (ICP) and diffuse reflectance spectroscopy. The obtained nanofibers were almost uniform and uniaxially aligned with their longitudinal axes oriented randomly and no entanglement was observed between them. It was also found that Cu(acac)₂ was embedded as distinct nanoparticles inside and over the walls of the nanofibers. The obtained nanocomposite was successfully used as a recoverable heterogeneous catalyst in the Michael addition reaction of carbon nucleophiles such as malononitrile, indole and 2-methylindole to various α,β-unsaturated carbonyl compounds. The Michael addition reaction proceeded smoothly at room temperature in dry THF. Under very mild reaction conditions, good to excellent yields of the desired products were obtained. Although one favorable feature of the catalyst was ease of recycling, a minor decrease in its efficiency during successive runs was observed. It was found that 7% decrease in efficiency after four successive runs may be due to the slight leaching of Cu(acac)₂ into the solution based on an ICP analysis of the recovered catalyst of the fourth run.     

Construction of S-box based on chaotic Boolean functions and its application in image encryption

In numerous encryption frameworks, the first information is changed into encoded form by applying nonlinear substitutions and affecting diffusion. The goal of the nonlinear change is to accomplish high level of randomness in the image content. The choice of the source of randomness is critical because the success in cryptanalysis is demarked by the characteristics identified in the encrypted data. The chaotic frameworks show random conduct that is suitable for encryption applications where nonlinear transformations are needed in the middle of plaintext and the scrambled information. The application of nonlinear functional chaos-based system with embedded chaotic systems and binary chaotic sequences can prompt randomness and diffusion in the information. In addition to the high state of randomness, the requirement for various round keys is needed in a run of the mill substitution–permutation process. The proposed strategy kills the requirement for different round keys, which is suitable for high-speed communication frameworks. The measurable analyses performed on the proposed nonlinear algorithm which show improvement in encryption quality and safety against numerous brute-force and statistical attacks. Also, the proposed framework demonstrates high safety against differential and linear cryptanalysis.     

Thermal Stability and Mechanical Properties of Organo-Soluble and Processable Polyimides for High-Temperature Materials

A new series of organo-soluble polyimides with pendant groups of methoxy or methyl of azomethine diamine were synthesized through two-step process by chemical imidization. Such polyimides were tested for thermal and mechanical properties. Their thermal stability was studied in terms of temperature at 10% weight loss which ranged between 475 and 498°C with T_g around 240–278°C. Activation energy, enthalpy of the polyimides were calculated and ranged 31.12–43.59?kJmol^?1 and 29.46–41.93?kJmol^?1. Thermal, mechanical, and thermodynamic parameters demonstrated that the resulting polyimides can hold excellent application in the fields of high-performance, advanced composites, and high-temperature microelectronics.