Properties of Natural Rubber/Recycled Chloroprene Rubber Blend: Effects of Blend Ratio and Matrix

The present study investigated the effects of two types of natural rubber and different blend ratios on the cure, tensile properties and morphology of natural rubber/recycled chloroprene rubber blends. The blends of natural rubber/recycled chloroprene rubber were prepared by using laboratory two-roll mill. The result showed that the cure time prolonged with the addition of recycled chloroprene rubber (rCR). Comparability, natural rubber/recycled chloroprene rubber (SMR L/rCR) blendcured rapidly than epoxidized natural rubber/recycled chloroprene rubber (ENR 50/rCR) blend. The addition of rCRalso caused a decrement in the tensile strength and elongation at break for both rubber blends. The SMR L/rCR blendsshowed higher tensile strength and elongation at break compared to those of ENR 50/rCR blends at any blend ratios.     

Antioxidative and anticarcinogenic activities of methylpheophorbide a,isolated from wheat grass (Triticum aestivum Linn.)

Methylphophorbide a (MPa) has been isolated from the ethanol extract of the wheat grass plant. Its antioxidative efficacy is evaluated by hydroxyl radical scavenging activities and reducing capacity which are significantly up regulated in comparison with aqueous extract of the plant. The compound shows iron-binding capacity where the Fe²⁺ binds with MPa by two types of binding patterns with dissociation constants 157.17 and 27.89. It has antioxidative and cytotoxic effects on HeLa and Hep G2 cells. The cancerous cell survivability decreases with increasing concentration of MPa. These findings have provided evidence for the traditional use of the wheat grass plant in the treatment of cancers, oxidative stress and iron overloaded disorders.     

Effect of limonene on the frontal ring opening metathesis polymerization of dicyclopentadiene

The frontal ring opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) in the presence of limonene, using second generation Grubbs’ catalysts, is reported. The effect of limonene on the amount of catalyst and the typical frontal polymerization parameters, as maximum temperature (T_max) and velocity of the front (V_f), is studied. In addition, the influence of limonene on the mechanical properties of the polymeric samples is reported. Finally, a deep study on the swelling properties of polymers is done. It has been demonstrated that limonene acts as both inhibitor and solvent of the catalyst. The T_max, V_f, T_g, and Young modulus values decrease as the amount of limonene increases, and the polymer samples swell in THF depending on the amount of limonene. All results indicate that the limonene addition on FROMP of results in advantages on the polymerization reaction and its parameters and on the final polymer properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 63–68     

Elevation of modulus and elongation of semicrystalline polyurethanes

Polyurethanes were synthesized based on an amorphous polyester polyol, and different chain extenders, comparing the universally accepted symmetric chain extender (1,4‐butanediol) with an asymmetric (1,2‐propanediol) chain extender. The effect of incorporating a crystalline polyester polyol polyhexamethylene adipate (PHMA) was investigated. The resulting morphologies and tensile properties are dramatically different. Based on the thermal and infrared data obtained, the sample with the symmetric chain extender exhibits a phase‐separated morphology, which can change as a function of time and temperature. Conversely, the polyurethane with the asymmetric chain extender has a phase mixed morphology that remains stable under the same experimental conditions. Incorporating crystalline PHMA resulted in a substantial change in the mechanical properties of the materials, especially for the copolymer comprising asymmetric chain extender. The rate of crystallization and the degree of crystallization achieved depended on the type of chain extender used. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018     

Competing energy scales in high‐temperature superconductors: Ultrafast pump–probe studies

We present a review of photoexcited quasiparticle dynamics of cuprate and pnictide high‐temperature superconductors in regimes (temperature, doping) where different phases such as superconductivity, spin‐density‐wave (SDW) and pseudogap phases coexist or compete with one another. We start with the overdoped cuprate superconductor Y_1–xCa_x Ba₂Cu₃O_7–δ, where the superconducting gap and pseudogap coexist in the superconducting state. In another cuprate Tl₂Ba₂Ca₂Cu₃O_y, we ob‐ serve a competition between SDW and superconducting orders deep in the superconducting state. Finally, in the underdoped iron pnictide superconductor (Ba,K)Fe₂As₂, SDW order forms at 85 K, followed by superconductivity at 28 K. We also find the emergence of a normal‐state order that suppresses SDW at a temperature T * ～ 60 K and argue that this normal‐state order is a precursor to superconductivity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enantioselective Self‐Assembly of Triangular Dy3 Clusters with Single‐Molecule Magnet Behavior

Three pairs of enantiopure chiral triangular Ln₃ clusters, [Ln₃L_{RRRRRR/SSSSSS}(μ₃‐OH)₂(H₂O)₂(SCN)₄]?xCH₃OH?yH₂O ( R ‐Dy₃ , Ln=Dy, x=6, y=0; S ‐Dy₃ , Ln=Dy, x=6, y=1; R ‐Ho₃ , Ln=Ho, x=6, y=1; S ‐Ho₃ , Ln=Ho, x=6, y=1; R ‐Er₃ , Ln=Er, x=6, y=0; S ‐Er₃ , Ln=Er, x=6, y=1), have been successfully synthesized by a rational enantioselective synthetic strategy. The core of triangular Ln₃ is bound in the central N₆O₃ of the macrocyclic ligand, and the coordination spheres of Ln ions are completed by four SCN^? anions and two H₂O molecules in axial positions of the macrocycle. The circular dichroism (CD) and vibrational circular dichroism (VCD) spectra of the enantiomers demonstrate that the chirality is successfully transferred from the ligands to the resulting Ln₃ clusters. Ac susceptibility measurements reveal that single‐molecule magnet behavior occurs for both enantiopure clusters of R ‐Dy₃ and S ‐Dy₃ . This work is one of the few examples of the successful design of a pair of triangular Dy₃ clusters showing simultaneously slow magnetic relaxation and optical activity, and this might open up new opportunities to develop novel multifunctional materials.     

Bronsted acid-mediated reactions of aldehydes with 2-vinylaniline and biphenyl-2-amine

Herein we report simple Bronsted acid-mediated reactions of aldehydes with 2-vinylaniline and biphenyl-2-amine. Ultimately, the useful nitrogen-containing heterocycle derivatives are obtained. The electronic properties of the substituents on the aldehydes and 2-vinylaniline were investigated. It was found that molecules with both electron-donating and -withdrawing substituents were perfectly suitable substrates for this transformation, and the expected products were obtained in moderate to excellent yields.     

Assessment of nanocomposites based on unsaturated polyester resin/nanoclay under impact loading

The aim of this study is to investigate the performance of nanoclay reinforced unsaturated polyester (UP) resin under impact loads. Nanocomposite specimens containing nanoclay in 0, 1.5, and 3 (wt%) were prepared by melt mixing method. X‐ray diffraction, transmission electron microscopy analysis, scanning electron microscope photographs, and viscosity changes in liquid state resin confirmed exfoliation and intercalation of the nanoclay in the UP resin system used. Tensile modulus showed an increase with increase in nanoclay content. However, the tensile strength and elongation at break exhibited reducing performance with increase in nanoclay content. Izod impact test results indicated better performance for the specimens containing nanoclay reinforcements, with 1.5 (wt%) of nanoclay specimens showing the highest value. High velocity impact tests were carried out using gas gun in velocity range of 20–100 m/sec and harden steel hemispherical tip projectile with diameter of 8.7 mm and weight of 11.54 g. Results for high velocity impact test indicated better performance by the specimens containing nanoclay, with 1.5 (wt%) nanoclay showing the highest attained value. Damage assessments of impact area for all specimens showed spalling type brittle failure with punch out and sever fragmentation pattern. Copyright © 2011 John Wiley & Sons, Ltd.     

On modifying properties of polymeric melts by nanoscopic particles

We study geometric and energetic factors that partake in modifying properties of polymeric melts via inserting well‐dispersed nanoscopic particles (NP). Model systems are cis‐1,4‐polybutadiene melts including a single atomic clusters of size varied in the range 10–150 atoms (3–7 Å in radius; 0.1–1.5% v/v). We modify the interactions between the chains and the particle by tuning attractive van der Waals interactions. Using molecular dynamics, we study equilibrium fluctuations and dynamical properties at the interface. The NPs move in the polymer matrix in two different regimes corresponding to trapped and free diffusion, depending on the NP size. Furthermore, degree of crowding around the NP by the polymer chains is quantified. Effect of NP size and interaction strength both on volume and volumetric fluctuations is manifested in mechanical properties, quantified here by bulk modulus, K. Tuning NP size and nonbonded interactions results in ～15% enhancement in K by addition of a maximum of 1.5% v/v NP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

High‐TC Ferromagnetic Semiconductor‐Like Behavior and Unusual Electrical Properties in Compounds with a 2×2×2 Superstructure of the Half‐Heusler Phase

Heusler phases, including the full‐ and half‐Heusler families, represent an outstanding class of multifunctional materials on account of their great tunability in compositions, valence electron counts (VEC), and properties. Here we demonstrate a systematic design of a series of new compounds with a 2×2×2 superstructure of the half‐Heusler unit cell in X–Y–Z (X=Fe, Ru, Co, Rh, Ir; Y=Zn, Mn; Z=Sn, Sb) systems. Their structures were solved by using both powder and single‐crystal X‐ray diffraction, and also directly observed by using high‐angle annular dark‐field imaging in a scanning transmission electron microscope (HAADF‐STEM). The VEC values of these new compounds span a wide and continuous range comparable to those for the full‐ and half‐Heusler families, thereby implying tunability in compositions and physical properties in the superstructure. In fact, we observed abnormal electrical properties and a ferromagnetic semiconductor‐like behavior with a high and tunable Curie temperature in these superstructures.