Regioregulated Syntheses of Poly(aminopyridine)s by Pd‐catalyzed Amination Reaction

Regioregulated poly(aminopyridine)s were synthesized by a Pd‐catalyzed C N coupling reaction. The polymerization using Pd(0) and a bulky monodentate phosphine ligand distinctively produced the para‐linked and meta‐linked poly(aminopyridine)s, without the need for a protection process. The regioregularity of the polymer was confirmed by ¹H NMR spectroscopy. Model reactions were studied to evaluate the possibility of crosslinkage in the polymer. A large difference in reactivity was observed between 5‐amino‐2‐bromopyridine and 2‐amino‐5‐bromopyridine, which should have afforded same product. Density functional theory (DFT) calculations indicated that electron densities of the Br‐bound carbon atom and the pyridine‐nitrogen atom determine the reactivity of the monomers.

     

Palladium(0)-catalyzed cyclization of electron-deficient enynes and enediynes

In the presence of a Pd(0) precatalyst, Pd2(bq)2(nbe)2 or Pd2(dba)3, 1,6-enyne esters were heated in refluxing benzene to give cyclodimers as single regioisomers. On the other hand, the combination of the Pd(0) precatalyst and triphenyl phosphite gave rise to various cycloisomerization products depending on the substitution pattern of the enyne esters. Six-membered ring cycloisomerization products were predominantly obtained from enyne esters bearing methallyl or 2-phenyl-2-propenyl moieties, while other enyne esters afforded normal five-membered ring cycloisomerization products. Intramolecular [2 + 2 + 2] cyclocotrimerization of enediyne esters also proceeded in the presence of the Pd(0) precatalyst and triphenylphosphine to give fused cyclohexadienes.     

Effect of polymer entanglement on the toughening of double network hydrogels

The mechanical strength of double network (DN) gels consisting of highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first component and linear polyacrylamide (PAAm) as the second component has been investigated by varying the molecular weight of the second polymer PAAm, M(w). The experimental results reveal that, for toughening of the DN gels, (1) M(w) is one of the dominant parameters; (2) there is a critical value of M(w) = 10(6) for a remarkable enhancement; (3) the fracture energy of DN gels with a M(w) larger than 10(6) reaches a value as high as 10(3) J/m(2). By plotting the strength of DN gels (fracture stress sigma and fracture energy G) against a characteristic parameter of c[eta], where c is the average concentration of PAAm in the DN gels and [eta] is the intrinsic viscosity of PAAm, it is found that the dramatic increase in the mechanical strength of the DN gels occurs above the region where linear PAAm chains are entangled with each other. Thus, we conclude that the entanglement between the second component PAAm plays an important role of the toughening mechanism of DN gels. This result supports the heterogeneous model, which predicts the presence of "voids" of the first network PAMPS with a size much larger than the radius of the second polymer PAAm.     

Beschleunigung der Sedimentation im helixförmigen Rohr

Ohne Zusammenfassung     

Piezo-optical study of excitons in KI

The effects of a uniaxial stress along 〈001〉 or 〈110〉 direction on the excitonic structures of KI are studied between 5.5 and 7.5 eV at room temperature by a piezo-modulation technique. Stress dichroism leads to the conclusion that either the second or the third peak corresponds to a transition at the Γ point in the Brillouin zone forming a spin-orbit pair with the first exciton and the other to a transition at the L point. The fourth peak is ascribed to a transition at the L point with an overlaping one at the X point.     

Time-dependent mechanical symmetries and extended Hamiltonian systems

Time-dependent mechanical symmetries are discussed in the framework of an extended Hamiltonian system. The Lie-algebraic structure of the time-dependent symmetry is made clear by introducing an extended Poisson bracket. Moreover, the relationship between the symmetry algebras of the classical and the quantum system is established.     

Formation of β-alumina type potassium gallate and its ionic conductivity

Mixtures of Ga₂O₃ and K₂CO₃ in the composition range of $\text{Ga}{}_2\text{O}{}_3\text{K}{}_2\text{O}\text{= 4–9}$ were sintered at various temperatures. X-ray diffraction patterns showed that the specimens of $\text{Ga}{}_2\text{O}{}_3\text{K}{}_2\text{O}\text{= 4, 5,}\text{and}\text{6}$ had a β-alumina type structure. K₂O·5Ga₂O₃ sintered at 1500°C belonged to the hexagonal system which was β phase, similar to Na-βAl₂O₃, while that sintered at 1200°C belonged to the rhombohedral system corresponding to the β″ phase, similar to Na-β″Al₂O₃. The assignments of indices to their diffraction lines were tried and the crystal structure of the β phase was presumed. The ac conductivities of the β and β″ phases were measured by the use of an impedance bridge, and the ionic transport numbers were examined by a dc polarization technique and Tubandt's electrolysis method. The compounds were revealed to be potassium ion conductors.