Rheological properties of linear and crosslinked polymer blends: Relation between crosslink density and enhancement of elongational viscosity

Strain‐hardening behavior in the elongational viscosity of binary blends composed of a linear polymer and a crosslinked polymer, in which the molecular chains of the linear polymer were incorporated into the network chains of the crosslinked polymer, was studied. Blending the crosslinked polymer characterized as the gel just beyond the sol–gel transition point greatly enhanced the strain‐hardening behavior in the elongational viscosity, even though the amount of the crosslinked polymer was only 0.3 wt %. However, the crosslinked polymer, which was far beyond or below the sol–gel transition point, had little influence on the elongational viscosity as well as the shear viscosity. The stretching of the chain sections between the crosslink points was responsible for the strain‐hardening behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 228–235, 2001     

Structure and mechanical properties for binary blends of polypropylene and ethylene‐1‐hexene copolymer

The structure and mechanical properties of the injection‐molded products for the binary blends composed of an isotactic polypropylene (PP) and a rubbery ethylene‐1‐hexene copolymer (EHR) were studied. The following two types of blends were employed: one is the incompatible blend of PP and ethylene‐rich EHR; the other is the compatible blend of PP and 1‐hexene‐rich EHR. The incompatible blend shows a phase‐separated morphology, in which EHR domains in the skin layer highly orient to the flow direction. On the other hand, the compatible blend shows fairly homogeneous morphology in the skin and core regions, in which EHR molecules are dissolved into the amorphous PP region. The measurements of birefringence and infrared dichroism revealed that the magnitude of molecular orientation along the flow direction for the compatible blend is larger than that for the incompatible blend. Nevertheless, it was also found that anisotropy of the mechanical properties for the compatible blend is less prominent, which is attributed to lack of the mechanical connection between neighbor crystalline fragments aligned perpendicular to the flow direction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 701–713, 1999     

Structure and properties for binary blends of isotactic-polypropylene with ethylene-α-olefin copolymer. 1. Crystallization and morphology

Morphology and isothermal growth rates of spherulites for the binary blends consisting of an isotactic polypropylene (i-PP) and an ethylene-1-hexene rubber (EHR) were examined as a function of the crystallization temperature ranging from 388 K to 418 K. In this study, two types of EHR's were employed: “ethylene rich” EHR and “1-hexene rich” EHR. The blends of i-PP with the EHR of 51 mol % 1-hexene are miscible in the molten state, whereas the blends with the EHR of 33 mol % 1-hexene are immiscible in the molten state. It is found that the isothermal spherulite growth rate of the miscible i-PP/EHR blends decreases with increasing the EHR fraction, whereas the spherulite growth rate of the immiscible i-PP/EHR blends is independent of the blend composition and is the same as that of the i-PP. Optical microscope observation of the miscible blends crystallized isothermally shows that there are no rubber domains either in the intraspherulitic or in the interspherulitic contact regions. On the other hand, the immiscible i-PP/EHR blends show a phase-separated morphology. Furthermore, the number of tangential lamellae of the miscible i-PP/EHR blends is found to be increased by blending of the EHR, leading to the spherulite with negative birefringence. The sign of birefringence of spherulites is unaffected by the regime transition as well as by the fold surface free energy. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 953–961, 1997     

Biomimetic Oxidation of Aldehyde with NAD+ Models: Glycolysis-Type Hydrogen Transfer in an NAD+/NADH Model System

Just like in biological systems , the GAPDH-catalyzed oxidation of aldehyde to carboxylate proceeds in conjunction with 1,4-selective reduction of NAD⁺ to NADH model compounds [Eq. (1)]. The combination of GAPDH- and LDH-type transfer reactions is also described here as a system mimic for the NAD⁺/NADH redox cycle in anaerobic glycolysis. GAPDH=D -glyceraldehyde-3-phosphate dehydrogenase, LDH=L -lactate dehydrogenase.     

Synthetic Studies on Ciguatoxin: A Convergent Strategy for Construction of the F–M Ring Framework

Exceptional neurotoxicity is associated with ciguatoxin. The ciguatoxin mimic 1 , which contains the F–M framework of the natural product, has been prepared through a convergent synthesis. The two key steps were a Lewis acid mediated intramolecular reaction of a γ-alkoxyallylsilane with an acetal group and an SmI₂-mediated intramolecular Reformatsky reaction that permitted construction of the annelated hexahydrooxonin ring system.     

Measurement of specific surface free energy of ruby and quartz single crystals using contact angle of liquids

The specific surface free energy of ruby and quartz single crystal was experimentally obtained using contact angle of water and formamide droplets on the crystal surfaces, and compared with the morphology of each crystal. The ruby crystals satisfied Wulff's relationship even though their shape were not equilibrium form. The specific surface free energies of the growing faces of synthetic quartz crystal, ‐X, +X, Z, and S faces were obtained as 51.9, 55.6, 57.4, and 58.9 mN/m, respectively. The growth rates of these faces were 0.09, 0.23, 0.28, and 0.33 mm/day, respectively. The growth rate of each face of the quartz crystal can be regarded as a function of the experimentally obtained specific surface free energy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Isolation and analysis of tetraheme-bound-cytochrome from photosynthetic reaction centers of Rhodopseudomonas viridis

A tetraheme cytochrome (BCytc) was isolated from the photosynthetic reaction centers (RC) of Rhodopseudomonas viridis while maintaining the redox activity. BCytc was removed from the H-subunit-detached RC by polyacrylamide electrophoresis using an alkyl ether sulfate mixed with sodium dodecyl sulfate. Redox titration of BCytc showed a simple one-step redox titration curve and a lowered midpoint potential than that of one in RC. Direct electron transfer between BCytc and electrode surfaces, such as indium tin oxide, was successfully performed, indicating a potential for molecular electronic material.     

Gas-phase stability of cluster ions SF m + (SF6) n with m = 0–5 and n = 1–3

The gas-phase stabilities of cluster ions SF⁺_m (SF₆)_n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF⁺_m (SF₆)₁ were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF⁺_m (SF₆)_n with m = 0−4. The structures of SF⁺₅, SF⁺ (SF₆)₁, SF⁺₃ (SF₆)₁, and SF⁺₅ (SF₆)₁ were investigated by ab initio molecular orbital calculations. For SF⁺₅, the D_3h geometry is found to be most stable andC_4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures.