Evidence for atomic recondensation on ion-bombarded solid surfaces

Direct evidence is presented that vapor-phase crystal growth is induced on solid surfaces bombarded with inert-gas ions. Surface cones formed on AlGaAs/GaAs superlattice targets exposed to a few keV Ar⁺ ions were characterized as polycrystalline cone tips protruding beyond the original target surface. Fine particles were also found to grow in close vicinity to the cone evolution sites, thus demonstrating that target atoms ejected from the impact area condensed into polycrystalline cone tips and particles, as a result of an enhanced particle supply to the projected areas. Since this finding is not within the current knowledge of ion-solid interactions, a new theoretical approach is required for its interpretation.     

New approach to block copolymerization of ethylene with polar monomers by the unique catalytic function of organolanthanide complexes

This paper describes the first examples of ABA‐ and AB‐type block copolymerizations of a nonpolar monomer, in this case ethylene, with polar monomers, such as methyl methacrylate (MMA), ϵ‐caprolactone (CL), and 2,2‐dimethyltrimethylene carbonate (DTC), initiated by the unique catalytic function of rare earth metal complexes [Sm(II) and Ln(III) (Ln = Y, Sm)] as initiators. The Sm(II) species conducts the ABA‐type triblock copolymerization, leading to poly(MMA‐co‐ethylene‐co‐MMA), poly(CL‐co‐ethylene‐co‐CL), or poly(DTC‐co‐ethylene‐co‐DTC) by the efficient catalysis of racemic Me₂Si(C₅H₂‐2‐Me₃Si‐4‐tBu)₂Sm(THF)₂ ( 1 ) or meso Me₂Si(Me₂SiOSiMe₂)(C₅H₂‐3‐tBu)Sm(THF) ( 2b ). The resulting block copolymers are completely insoluble in THF and CHCl₃, but the homopolymers of MMA, CL, and DTC are freely soluble in these solvents. TEM profiles provide direct evidence for the block copolymerizations, where the spheric morphology of homogeneously dispersed polar polymers was observed. Ln(III) species, such as racemic Me₂Si(C₅H₂‐2‐Me₃Si‐4‐tBuMe₂Si)YH ( 5 ) and Me₂Si(C₅H₂‐2‐Me₃Si‐4‐tBu)SmH ( 6 ), afford AB‐type block copolymers between ethylene and MMA or CL, whose TEM images reveal the homogeneous dispersion of poly(MMA) or poly(CL) units in the polyethylene region. The ABA‐ and AB‐type block copolymers demonstrate high break stress and high tensile modulus as compared with their corresponding blended polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4095–4109, 2000     

An Efficient and Concise Enantioselective Total Synthesis of Lactacystin

A selective, irreversible inhibitor of proteasome function , lactacystin ( 1 ) is an important experimental tool in cell biology. An efficient and direct enantioselective synthesis of lactacystin proceeds via the intermediates shown below. This process allows for the first time easy access to analogues of lactacystin in which the isopropyl substituent is replaced by other lipophilic groups. PMB=p-methoxybenzyl.     

Structure development under transient shear flow in semidilute polystyrene solution

The shear-induced concentration fluctuations or phase separation of a semidilute solution comprised of polystyrene (PS) as a solute and dioctylphthalate (DOP) as a solvent (PS/DOP) was investigated by using real-time and in-situ shear-small-angle light scattering and shear-phase-contrast optical microscopy. When a transient shear flow with a fixed shear rate γ greater than a critical value γ_C was imposed on the solution, a unique anisotropic scattering pattern was observed some time after onset of shear. This pattern was found to be identical to the “butterfly pattern” previously reported for the same solutions under steady shear flow with γ_C. When the shear flow was ceased before the scattered intensity reached a steady state, the scattered intensity rapidly increased toward a maximum intensity, and then decreased toward the intensity of the quiescent solution with time. From the phase-contrast microscopy, this immediate increment of the scattered intensity after the shear cessation was found to arise from the increment in amplitude of the concentration fluctuations along flow direction. The characteristic length scale of the fluctuations was about 2.5 μm in this experiment, almost independent of the shear rate imposed on the solution.     

Living ring-opening polymerization of cyclic carbonate using cationic zirconocene complex as catalyst

Living ring-opening polymerization of the cyclic carbonate 1,3-dioxepan-2-one was achieved by using the cationic zirconocene complex [Cp₂ZrMe]⁺[B(C₆F₅)₄]⁻ as catalyst at room temperature. A linear relation between conversion and molecular weight of the obtained polymer was observed. Furthermore, block copolymerization of the cyclic carbonate and ε-caprolactone was successfully performed.