Synthetic applications of non-polymerizable monomers in living carbocationic polymerization

The foundation and methodology of using highly reactive but non-polymerizable monomers in living cationic polymerizations is introduced. The chemistry and kinetics of 1,1-diphenylethylene (DPE) addition to living polyisobutylene (PIB) in methyl chloride/n-hexanes 40/60 v/v at −80°C is reported. Monoaddition occurred even when large excess of 1,1-diphenylethylene was used. The methanol quenched polymer of the DPE capped PIB carried -OCH₃ functionality exclusively, suggesting that the diphenyl alkyl chain-ends are completely ionized, which was confirmed by conductivity studies. By in-situ functionalization using soft nucleophiles a variety of functional groups were obtained, most notably ester upon reaction with silyl ketene acetal. It was found that the diphenyl carbenium ion is an efficient initiating species for the polymerization of reactive monomers such as vinyl ethers and α-methylstyrene. The synthesis of PIB based block copolymers was accomplished by sequential monomer addition, using para-methylstyrene, α-methylstyrene or isobutyl vinyl ether as the second monomer. It involved capping with DPE, followed by tailoring the Lewis acidity to the reactivity of the second monomer by the addition of titanium(IV) alkoxide, by replacing the Lewis acid with a weaker one or by the use of a common ion salt. PIB-b-PMMA was obtained by the combination of living cationic and group transfer (GTP) polymerizations.     

Partial Reduction of MgFe2O4 with Al and Mg via Ball Milling

Nanocomposites consisting of metallic Fe particles and a nonmagnetic oxide were prepared by reducing MgFe₂O₄ with Al or Mg in a ball mill. The reaction takes place as a fast self-propagating process sometime between 0.5 and 1 h of milling. Combining XRD and Mössbauer spectroscopy reveals that the bcc Fe phase contains a few percents of dissolved Al, it has a high defect concentration, and the surface tension of the ultrafine (about 15 nm) grains results in local compressive strains. The magnetization is 25% less than expected for pure ferromagnetic Fe.     

Enantioselective alkylation of chiral enolates

Alkylations of chiral amide enolates derived from (?)-prolinol have been shown to yield versatile hydroxy-amides in high diastereomeric purity. Their use in the preparation of optically active carboxylic acids is described.     

Ringerweiterungen an Benzochinol-acetaten, 2. Mitt.: Synthese von Troponen aus Benzochinolacetaten; β-Alkylierung des o-Acetoxy-cyclohexadienonsystems; Herstellung von 2-Aminotroponen

Zusammenfassung Ausgehend von Phenolen bestimmter Konstitution kann man mit Hilfe der o-Benzochinol-acetate durch Ringerweiterung mit Diazomethan—Bortrifluorid zu Troponen mit derselben Substituentenfolge gelangen¹. Als Nebenprodukte treten die in Stellung 5 methylierten Chinolacetate und Tropone auf. Durch Variation der Substituenten in Stellung 1 und 5 des o-Cyclohexadienon-systems ist es möglich, die Ringerweiterung oder die Methylierung in Position 5 zur Hauptreaktion zu machen.Einwirkung von Hydrazinhydrat auf das Tropon liefert ein Gemisch aus 2-Amino- und 2-Hydrazinotropon. Hydrogenolyse der Hydrazinoverbindung mitRaney-Nickel gibt in guter Ausbeute die Aminoverbindung.Mit 1 Abbildung1. Mitt.:E. Zbiral, J. Jaz undF. Wessely, Mh. Chem.92, 1155 (1961).     

Inclusion complexes of cryptophane-E with dichloromethane and chloroform: A thermodynamic and kinetic study using the 1D-EXSY NMR method

Complexation equilibria and kinetics of exchange of chloroform and dichloromethane molecules between the cavity of cryptophane-E and bulk solution were investigated using NMR methods. Using one-dimensional magnetization transfer (1D-EXSY type sequence), chemical exchange rates were measured in different temperature ranges, limited by the equilibrium constant values of the complexes and the boiling points of the guest substances. From the kinetic data, activation energies were calculated using the Arrhenius equation. From the temperature-dependence of the association constant data, the enthalpy and entropy of complexation were estimated and compared with values for similar complexes of other cryptophanes.     

Oligo(vinylidene fluoride) Langmuir-Blodgett films studied by spectroscopic ellipsometry and the density functional theory

Thin films of amphiphilic vinylidene fluoride oligomers prepared by Langmuir-Blodgett deposition on silicone substrates were investigated by comparing experimental and theoretical mid-infrared (IR) spectra. The experimental spectra were obtained using infrared spectroscopic ellipsometry. Theoretical spectra were calculated using density functional theory. Excellent correspondence of major IR bands in both data sets shows that the molecular backbone is oriented with the long axis normal to the substrate plane. This is in contrast to poly(vinylidene fluoride) LB films, in which the polymer chains are parallel to the substrate.     

Search for weak random anisotropy effects in the critical region of Pd80Co20

Following a suggestion by I. A. Campbell, we have conducted Mössbauer source experiments on disordered alloys of⁵⁷CoPd₈₀Co₂₀ in search for evidence of random anisotropy (RA) effects on critical behavior. The result, β=0.38(3) in the reduced temperature range 10^?2<1?T/T_c<0.2, though not strictly asymptotic, is consistent with the d=3 Heisenberg model, with no evidence for RA. In this paper we argue that among transition metal ferromagnetic alloys there are no better candidates for RA effects than our chosen system.