Victor Desreux

Hydrodynamic properties and unperturbed dimensions of polycyclohexyl and polyphenyl methacrylates in various solvents

Abstract Intrinsic viscosity, sedimentation, light scattering and osmotic pressure measurements have been made on dilute solutions of polycyclohexyl (PCy) and of polyphenyl methacrylates (PPh). Relations between (η), (S0), second virial coefficient 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; Berrys relation fits best the experimental data. These dimensions calculated from the sedimentation data (Cowie-Bywater) and from the second virial coefficient data (Krigbaum) agree with those obtained by viscosity. The flexibility factor σ obtained for the two polymers is high, 2·5 (PCy) and 2·8 (PPh), confirming previous results on poly-β-naphthyl and polydecahydro-β-naphthyl methacrylates.(1) The fact that the aromatic polymers have higher σ values than the corresponding saturated polymers may be due to a specific interaction between the aromatic groups and to their higher rigidity.

Temperature dependence of the viscosity of dilute poly(β-naphthyl methacrylate) solutions

Abstract The temperature dependence of the actual viscosity of dilute poly(β-naphthyl methacrylate) solutions was described by an Arrhenius expression according to Moores treatment. The apparent activation energy of flow was found to be lower for solutions in benzene, toluene and tetralin than for solvent. In dioxane, a good solvent, the activation energy was nearly constant and close to that for the solvent. The pre-exponential terms were, in all cases, higher for solutions than for the solvents. The decrease in activation energy and increase in pre-exponential term are largely dependent on solvent power: the maximum effect is found in the poorest solvent. This behaviour is discussed in connection with the temperature dependence of the Mark-Houwink and of the Fox-Flory constants obtained from intrinsic viscosity data: the differences in the activation energy of flow and in the pre-exponential term between the solvent and the solutions are related to variation of coil expansion with temperature.

Electro-optical studies on synthetic polyelectrolytes—II: Electric birefringence of poly-N-butyl-4-vinylpyridinium salts in aqueous solution

Abstract The field strength dependence of the electric birefringence of poly- N -butyl-4-vinylpyridinium bromide in aqueous solution changes markedly with polymer concentration. Analysis of the orientation curves reveals that the mean electric polarizability −Δα sharply increases when the concentration decreases, as a result of the extension of the chain, while the negative optical anisotropy factor remains unchanged. An empirical relationship, similar to that found for the reduced viscosity, is derived for the variation of electric polarizability with concentration. Increasing the ionic strength produces a coiling of the polyelectrolytic chain and a decrease of − Δx . The replacement of the bromide ions by sulphate ions causes a conformational change evidenced by a decrease of −Δα and of the relaxation time. This effect is interpreted by the formation of electrostatic bonding between the pyridinium rings on non-adjacent segments of the chain, and to a limited extend, by intermolecular bonding. The dependence of the relaxation time, extrapolated to infinite dilution, on the molecular weight of the samples is analysed on the basis of a worm-like chain model. The persistent length obtained is found of the same order of magnitude as in the case of other semi-rigid polymers. The predominant influence of the segmental orientation on the optical, electric or conformational parameters is discussed in detail.

Hydrodynamic properties and unperturbed dimensions of polytert.butylacrylate in different solvents

Intrinsic viscosity, light scattering, and sedimentation data are reported for fractions of polytert.butylacrylate in different solvents and in a θ-solvent. The unperturbed dimension has been calculated by various methods; the Stockmayer-Fixman and Kurata-Stockmayer relationships gave the best fit for the experimental results in the different solvents; the flexibility (a) of the chains has been found to be between 2•2 and 2•3; this value seems to be indicative of an influence of the bulky side group.

Electro-optical studies on synthetic polyelectrolytes. IV. Electric polarizability and conformation of poly-N-methyl-2-vinylpyridinium bromide in aqueous solution.

Measurements of the relaxation time on aqueous solutions of the title polyelectrolyte as a function of the concentration and of the molecular weight show that its conformation at very high dilution can be better accounted for by a weakly bending rod or wormlike chain model, with persistence length ranging from 200 to 400 A. The analysis of the field strength dependence of the electric birefringence yields electric polarizability values which increase sharply with the dilution and are not significantly dependent upon the molecular weight. This has been tentatively interpreted on the basis of the theories derived by Oosawa and by Mandel and Van der Touw. The partially flexible model proposed by the latter authors allow to identify the electric polarizability calculated from electro-optical data to the specific dielectric increment measured in the high frequency range; both parameters appear to be molecular weight independent. The electric polarizability obtained from the Kerr effect would be originated in the induced dipoles caused by the delocalization of the bound counterions along rigid subunits whose length seems however to differ from the persistence length.

Electro-optical studies on synthetic polyelectrolytes: I. Ultraviolet electric dichroism of poly-N-alkylvinylpyridinium bromides in aqueous solution

The electric dichroism of aqueous solutions of poly-2- and 4-vinylpyridinium bromides has been measured in the 220 to 300 nm region. From the knowledge of the assignments of the absorption bands, the orientation of the pyridinium ring with respect to the macromolecular axis was determined for the poly-N-butyl-4-vinylpyridium bromide. An estimation of the birefringence contribution in the visible region originating from these ultraviolet dichroic bands revealed that the negative birefringence observed mainly arose from electronic transitions at shorter wavelengths.

Temperature dependence of the viscosity of dilute solutions of poly(2-chlorophenyl methacrylate) and poly(2,4,5,-trichlorophenyl methacrylate) in various solvents

Abstract According to Moores treatment, an Arrhenius expression was used to describe the temperature dependence of the actual viscosity of dilute solutions of poly(2-chlorophenyl methacrylate) and poly(2,4,5-trichlorophenyl methacrylate) in various solvents. The effect of the polymer on the activation energy for viscous flow was found to be negative in poor and moderate solvents (toluene, benzene and dioxane) and positive in a good solvent (THF). Irrespective of the nature of the solvent, the presence of polymer chains in solution led to an increase of the pre-exponential factor of the Arrhenius expression. The parameters of Moores treatment are discussed in comparison with the Fox-Flory and the Kuhn-Mark-Houwink relations. The observed behaviours can be primarily related to variations in coil expansion with temperature.

Electro-optical studies on synthetic polyelectrolytes—III: Electric birefringence of poly-n-alkyl-4-vinylpyridinium bromides in various solvents

Abstract The field strength dependences of the electric birefrigence of poly- N -butyl-4-vinylpyridinium (4-PVP · BuBr) samples have been measured in water and in various organic polar solvents. The observed change of sign of the birefringence, negative in water and positive in nitromethane, is explained by considering the respective influences of the intrinsic and form optical anisotropies. The lower degree of extension of the polyelectrolyte in some organic solvents is attributed to a lower degree of dissociation of the ionic sites. The influence of the dielectric constant and of the functional character of the solvent on the dissociation and solvation processes of the ionic sites is taken into account. Relaxation measurements in dimethylsulphoxide as a function of the molecular weight allow quantitative expression of the degrees of extension and of rigidity of the polyelectrolyte; the presence of aggregates has also been detected in DMSO solutions. A long alkyl chain, such as octyl, attached to the quaternary pyridinium groups strongly modifies the conformation of the polyelectrolyte and a polyelectrolyte-polysoap transition has been observed as a function of the solvent composition in water-ethanol mixtures.