Hydrodynamic Properties and Unperturbed Dimensions of Polydecahydro- β -naphthyl and Poly- β-naphthyl Methacrylates in Different Solvents

Abstract

Intrinsic viscosity, sedimentation, light-scattering, and osmotic-pressure measurements have been carried out at 25° on dilute solutions of polydecahydro-β -naphthyl meth-acrylate (PDNa) and of poly-β-naphthyl methacrylate (PNa). For both polymers, the degree of polydispersity was around 1.5 and the molecular weight range was large: 10⁵ to 3 × 10⁶. Relations between [η], [S₀], A₂, and molecular weight have been established.

The applicability of the different theories (Stockmayer-Fixman, Kurata-Stockmayer, Fox-Flory, Cowie, Berry, Kamide-Moore) for the determination of the unperturbed dimensions from the viscosity data is discussed; Berry's relation best fits the experimental data.

These dimensions, calculated from the sedimentation data according to the Cowie-Bywater relation, agree with those obtained by viscosity. The flexibility factor is 2.9 for PDNa and 3.1 for PNa. These large values are a consequence of the presence of very bulky groups in the side chain; however, the higher η value for PNa led to the assumption that a specific interaction between the aromatic rings influences the rigidity of the main chain.     

Proprietes dynamo-optiques du bromure de poly-N-butyl-4-vinylpyridinium dans differents solvants

Flow birefringence measurements on polybutylvinylpyridinium bromide have confirmed the change of the sign of the optical anisotropy previously observed by the electric birefringence method. The birefringence is negative in aqueous media, but positive in some organic solvents such as nitromethane. The estimation of the intrinsic optical anisotropy shows that this parameter is negative in water as well as in nitromethane; this is consistent with an orientation of the pyridinium lateral group perpendicular to the long axis of the particle. The positive sign of the birefringence displayed in nitromethane can be attributed both to an important contribution of form anisotropy, and to a pronounced decrease of the intrinsic optical anisotropy; the latter is explained by a conformational change of the polyelectrolyte which becomes more coiled and more flexible in solvents of lower dielectric constant.     

Gadolinium DOTA chelates featuring alkyne groups directly grafted on the tetraaza macrocyclic ring: synthesis, relaxation properties, "click" reaction, and high-relaxivity micelles

This paper reports on the synthesis and relaxivity properties of tetraacetic DOTA-type chelating agents featuring one or two alkyne groups directly grafted on the tetraaza macrocyclic ring and available for "click" reactions with azide-bearing substrates. The racemic DOTAma ligand bearing one alkyne group was obtained by a bisaminal template route. The same approach was used to prepare ligand DOTAda substituted by two alkyne groups located on two adjacent carbon atoms. The S,S enantiomer of DOTAda was also prepared by a "crab-like" condensation. This ligand is the first example of a DOTA derivative featuring two reactive functions adjacent to each other on the macrocyclic ring. A triacetic monoalkyne ligand (DO3ma) was also synthesized for comparison purposes. NMR studies indicate that the Yb(III) chelates of DOTAma and DOTAda adopt two conformations in solutions in which the tetraaza ring is rigidified. The hydration state of the Eu(III) chelates was determined by luminescence spectroscopy, and the water exchange time of the Gd(III) complexes was measured by (17)O NMR. Ring substitution accelerates the water exchange. These data were used to interpret nuclear magnetic relaxation dispersion curves of the Gd(III) chelates. Two long aliphatic chains have been added to DOTAda by a "click" procedure to form the (C18)(2)DOTAda ligand. The corresponding Gd(III) complex forms micelles of unusually high relaxivity presumably because of the close proximity of the aliphatic chains on the macrocyclic ring that ensures a rigid double anchoring into the micelles.     

Mikrotaktizit?t und hydrodynamisches Verhalten von Poly(trimethacrylat), dargestellt in Hexamethyl phosphortriamid

Ohne Zusammenfassung     

Electrochemical behaviour of a snake-cage cation-exchange membrane electrolytic sorption and ionic conductivity

Summary The uptake of electrolyte by a snake-cage cation-exchange membrane has been measured by different methods. The experimental data are interpretable by local application of theDonnan law and consequently result from the heterogeneous structure of the membrane. The ionic conductivity measurements confirm these results. No ion-exchange polymer is imprisoned in the superficial layers of the membrane, but it is concentrated in a central zone of maximum capacity. Moreover, the development of continuous and poorly charged pores enhances the structural heterogeneity and lowers the permselectivity. If the snake-cage technique is very versatile to insolubilise many different groups, the structure of the resulting systems must be controlled by an adequate choice of matrix porosity and imprisoned chain length.

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Zusammenfassung Die Elektrolytkonzentration in einer Snake-Cage-Kationenaustauschermembran wird mit verschiedenen Methoden gemessen. Die experimentellen Ergebnisse lassen sich durch lokale Anwendung desDonnan-Gesetzes erklären und folgen demgemäß aus der heterogenen Membranstruktur. Die Leitfähigkeitsmessungen bestätigen die früheren Ergebnisse. Kein Ionenaustauscherpolymeres wird in den oberflächlichen Membranschichten festgehalten, es wird vielmehr in einer zentralen Zone mit der Maximalaustauschkapazität konzentriert. Darüber hinaus vergrößert die Anwesenheit von durchgehenden und schwach geladenen Poren die strukturelle Heterogenität und verkleinert die Permselektivität. Wenn viele verschiedene Gruppen durch die Snake-Cage-Technik unlöslich gemacht werden, was möglich ist, so muß die Struktur der entsprechenden Systeme durch eine angemessene Wahl der Matrix-Porosität und der Längen der festgelegten Ketten kontrolliert werden.

     

60Co-initiated polymerization of styrene,vinyl acetate,and their mixtures in the presence of a radical initiator

Styrene and vinyl acetate have been polymerized by γ-radiation in the presence of α,α′-azobisisobutyronitrile or benzoyl peroxide. Benzoyl peroxide does not affect the vinyl acetate polymerization, but the rate of polymerization is greatly increased by the action of the initiator in the case of the following systems: styrene–α,α′-azobisisobutyronitrile, styrene–benzoyl peroxide, and vinyl acetate–α,α′-azobisisobutyronitrile. For these three systems, the experimental results are in good agreement with a kinetic scheme obtained by assuming an energy transfer process from monomer excited molecules to the initiator; this process does not occur in the first system, and the initiation rate is determined only by the vinyl acetate concentration. In the case of the polymerization of mixtures of the two monomers, the action of α,α′-azobisisobutyronitrile and that of benzoyl peroxide are practically the same; that is, the shape of the polymerization curve may be understood on the basis of an energy transfer from styrene excited molecules to the initiator.