Asymmetric Allylation Polymerization of Bis(allylsilane) and Dialdehyde

The enantioselective addition of an allylsilane to an aldehyde is an excellent method to give optically active homoallyl alcohols. Applying this reaction to the asymmetric polymerization of bis(allylsilane) and dialdehyde, the synthesis of a new optically active polymer having chirality on the main chain was possible. Chiral acyloxyborane (CAB) was effective as a catalyst in this asymmetric allylation polymerization.     

A computational study of base‐catalyzed reactions between isocyanates and epoxides affording 2‐oxazolidones and isocyanurates

Title reactions were investigated with ab initio calculations. Methyl isocyanate and ethylene oxide were adopted as model reactants. The products, 2‐oxazolidones and isocyanurates, cannot be yielded without a base catalyst. The 2‐oxazolidone may be produced by a dual S_N2 reaction, where the catalyst base (e.g., Cl⁻) is a nucleophile and a leaving group on the ethylene–oxide carbon. Isocyanurate is generated by the stepwise association of three isocyanate molecules, where one of the molecules is initially linked with a base. The six‐membered ring isocyanurate is isomerized stepwise into the components isocyanate and 2‐oxazolidone. A tetrahedral type of complex between the isocyanurate and a base‐catalyzed ethylene oxide is the key intermediate for the isomerization. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 316–326, 2001     

Storage Modulus and Surface Morphology of Poly(vinyl alcohol)/Alumina Hybrid Hydrogels

The storage moduli, shear moduli and surface morphologies of poly(vinyl alcohol) (PVA) and alumina hybrid hydrogels were investigated. The storage moduli of hybrid hydrogels with higher alumina contents were found to be 1.5 times higher than those of PVA gels. This increase in modulus might be attributed to the cohesion of alumina to the PVA network.

SEM photograph of Al7 PVA/alumina hybrid hydrogel. The photograph was taken with a magnification of × 220.     

Gravitational Effects on Mixing and Growth Morphology of an In0.5Ga0.5 System

A mixing experiment of multicomponents melts was performed using a uniform temperature furnace in the Second International Microgravity Laboratories (IML-2) mission. Growth morphologies and Ga concentration profiles were analyzed for the samples with the compositional ratio of 0.5 In–0.5 Ga–1.0 Sb grown under microgravity and on earth. The sample with free surface grown under microgravity was nearly spherical in shape, except some parts with projections. Ga was dispersed homogeneously in the bulk because the mixing was enhanced by Marangoni convection due to the concentration gradient. On the other hand, the sample grown on earth was a double cylindrical shape with different diameters, and Ga concentration decreased from top to bottom, showing clearly the effect of gravity. Many needle crystals were formed in both space and earth samples due to rapid cooling. The average size of the needle crystals grown in space was larger than that of the earth sample.