Diffusion and flow birefringence of alkylene-aromatic thermotropic polyesters (original) (raw)
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Kerr effect in solutions of a thermotropically mesogenic alkylene-aromatic polyester
European Polymer Journal, 1986
Electric birefringence (EB, Kerr effect) has been investigated for solutions of fractions of thermotropically liquid-crystalline alkylene-aromatic polyester (PE-10) and of its monomer. A very specific dependence of EB on the molecular weight (M) of the polymer was tbund: for low molecular weight substances the Kerr constant is negative, changes its sign with increasing M and, in the range of positive values, increases with M. These data are in quantitative agreement with the dependence of K on M predicted by the EB theory for kinetically rigid worm-like chains in which the longitudinal components of dipole moments of monomer units are "'accumulated" with increasing chain length. The detected relationships show that in PE-10 solutions the Kerr effect is due to the large-scale chain motion in which the behaviour of a dipole molecule is similar to the motion of a kinetically rigid particle rotating as a whole by the action of the field.
Polymer, 1973
The flow birefringence of a number of solutions of a poly(amide carboxylic acid) from pyromellitic anhydride and benzidine was measured at 30°C. N,N-dimethyl acetamide was used as a solvent. Addition of the organic base triethylamine to this polyacid (0 to 15g-equiv. with respect to the number of-COOH-groups) results in a strong increase of the stressoptical coefficient. This increase can successfully be interpreted in terms of an expansion of the molecular coils. An increase of the stress-optical coefficient is also obtained, when the concentration of the poly(amide carboxylic acid) is decreased. This is in agreement with the observed increase of the reduced viscosity, ~sp/C. A relation is deduced, which describes the dependence of the stress-optical coefficient on concentration with reasonable accuracy. Making use of this relation the degree of expansion of this polyelectrolyte can be determined for infinite dilution. From the behaviour of the extinction angle the conclusion is drawn that the hydrodynamic behaviour of the investigated polyelectrolyte molecules does not undergo a fundamental change with expansion: after a correction for polydispersity the results seem to indicate that the expanded molecules still approximately behave like Gaussian chains.
Organic Electronics, 2007
We report investigation of optical and electrical properties of poly(9-vinylcarbazole) (PVK) doped with 30 wt% 4-dibutylamino-4 0 -nitrostilbene (DBANS), depending on the molecular chain orientation of polar DBANS molecules. Orientation of dopant diode-like DBANS dye molecules was achieved by application of a static electric field through the polymer film, while heating the material near its glass transition temperature (T g ). Modification of optical properties due to the orientation was evidenced by the spectral dependencies of absorption coefficient. Appearance of the orientation-induced built-in electrical field was proven optically by the solid electric field induced second harmonic generation (SEFISHG) and electrically by current-voltage (IV) characterization. Measurement of the thermally stimulated currents (TSC) spectra demonstrated that carrier transport and trapping are affected, too. Changes of the TSCs induced by orientation were expressed best in the temperature range of 280-290 K. They could be attributed to the thermally activated process with activation energy of about 0.38 eV.
Journal of Research Updates in Polymer Science, 2017
Polarization far-IR spectroscopy has been used to carry out a comparative study of the spectra of granules and fibers of completely aromatic thermotropic liquid-crystal copolymer Vectra A950. The analysis of terahertz polarization IR spectra Vectra A950 showed that in contrast to the mid-IR, dichroic ratio of the absorption bands in the spectra of fibers and granules, substantially different. It is shown that the difference between the value and the orientation order parameter in the samples is determined by and correlated with the intensity of the local dynamics of polymer chains, such as the librational mobility of phenylene and naphthalene rings of the copolymer mesogens. The results suggest the possibility carrying out an independent evaluation of the spectroscopic parameters reflecting the properties of intermolecular interactions in oriented the liquid-crystalline polymers for their low-frequency spectra.
Viscosity and light scattering measurements of poly(2-fluoro-p-phenylene-2-fluoroterephthalamide)
Macromolecular Chemistry and Physics, 1995
We report on the characterization of the conformational properties of the fully aromatic polyamides poly(2-fluoro-p-phenylene-2-fluoroterephthalamide) (FPFT) in methanesulfonic acid using dynamic and static light scattering and viscosity measurements. The results are in quantitative agreement with a model of polydisperse wormlike chains for the solution conformation of FPFT. A comparison with the results obtained for the unsubstituted polymer poly(p-phenylenterephthalamide) (PFTA) under the same experimental conditions indicates that the introduction of halogen substituents on the aromatic rings has only a weak influence on the chain flexibility. a) Current address: DuPont Central Research & Development, Experimental Station, Wilmingb, Systematic IUPAC name: poly[imino(fluoro-1,4-phenylene)imino(fluoroterephthaloyl].
Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene
Polymer, 2012
Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (C n , with n ¼ 2, 6e16) in amorphous polystyrene at temperatures from 35 C to 165 C, that is, both below and above the polymer glass transition temperature of 100 C. All the mass uptake results are well described by a simple Fickian model (for t < t 1/2 ) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n 2 D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.
Diffusion of stabilizers in polymers. I. 2,4-dihydroxybenzophenone in polyolefins
Journal of Applied Polymer Science, 1975
The diffusion of the ultraviolet stabilizer 2,4dihydroxybenzophenone in compressionmolded sheets of low-density polyethylene, high-density polyethylene, and isotactic polypropylene was investigated over the temperature range of 44-75°C. The magnitude of the diffusion coefficients for these polyolefins was found to decrease in the order lowdensity polyethylene > high-density polyethylene > polypropylene, the corresponding activation energies being approximately 18, 23, and 34 kcal/mole. Studies under conditions of saturation indicated that the migration of this stabilizer was confined to the more accessible amorphous regions of the polymers. The rate of loss of stabilizer from polymer samples immersed in water was also investigated at 44°C. Values of the diffusion coefficients calculated from the results of these studies were somewhat greater than those determined from the diffusion studies for the low-density polyethylene and isotactic polypropylene samples and considerably smaller in the case of high-density polyethylene. The extraction studies also permitted the quantitative evaluation of the solubilities of the stabilizer in the polymers. These were found to be 0.003, 0.03, and 0.07 wt-% for high-density polyethylene, low-density polyethylene, and polypropylene, respectively, a t 44°C.