A.Yu. Bilibin

Diffusion and flow birefringence of alkylene-aromatic thermotropic polyesters

Abstract Hydrodynamic and optical properties of dilute solutions of polydecamethylene-terephthaloyl-di- p -oxybenzoate (P-10-TOB), polypentamethylene-terephthaloyl-di- p -oxybenzoate (P-5-TOB) and polytetramethylene-terephthaloyl-di- p -oxybenzoate (P-4-TOB) in dichloroacetic and trifluoroacetic acids were investigated by translational diffusion, velocity sedimentation, viscometry and flow birefringence. The results of hydrodynamic investigations are interpreted from the standpoint of theories taking account of the draining effect in macromolecules. It is shown, on the basis of hydrodynamic and optical data, that the equilibrium rigidity of molecules (the Kuhn statistical segment) is several times higher for P-10-TOB, P-5-TOB and P-4-TOB than for polyethyleneterephthalate.

Sterically hindered phenol–dextran conjugates: synthesis and radical scavenging activity

A new synthesis of the covalently bound conjugates of dextran and a sterically hindered phenol has been described. Some features of the synthetic procedure have been discussed. The conjugates were investigated as polymeric forms of antioxidants and their radical scavenging activity was studied in the reaction with diphenylpicrylhydrazyl. It was found that the radical scavenging activity of the conjugates was about three times higher in comparison with that of the mixture of a sterically hindered phenol and dextran.

Sterically hindered phenol–dextran conjugates: radical scavenging activity in water and water–organic media

The radical scavenging activity investigation of sterically hindered phenols–dextran conjugates was carried out in water and water–dioxane mixtures with use of sodium salt of 2,2-diphenyl-1-picryl-hydrazyl sulfonic acid (DPPH-SO3Na). The suggestion was made that the reaction mechanism includes the one-electron transition stage. It was found that the reaction rate constants of DPPH-SO3Na with the conjugates are higher than the ones with low-molecular weight model. One of possible reasons for obtained data could be the fact that dextran hydration shell stabilizes the cation-radical intermediate in case of conjugates better than bulk water.

Kerr effect in solutions of a thermotropically mesogenic alkylene-aromatic polyester

Abstract 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 found: 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.

Hydrodynamic and dynamo-optical properties of molecules of an aromatic polyester with para- and meta-phenyl rings in the main chain

Abstract The hydrodynamic and optical properties of molecules of an aromatic polyester (PE) dissolved in dichloroacetic acid have been investigated by the methods of translational diffusion, viscometry and flow birefringence. The chain of the PE investigated contains one phenyl ring in the meta-position alternating with three phenyl rings in the para-position. The Mark-Kuhn equations relating intrinsic viscosity and the translational diffusion coefficient to molecular weight have been obtained: [η] = 2.6 × 10−3 M1.1 cm3 g−1 and D = 5.6 × 10−5 M−0.70 cm2 sec−1. The results are interpreted in terms of theories of hydrodynamic and dynamo-optical properties of wormlike chains. It is shown that the PE macromolecules in solution exhibit equilibrium rigidity determined by the length of the Kuhn statistical segment A = 120 ± 20 A and the anisotropy of unit chain length β = 5 × 10−17 cm2.

Molecular Weight Determination of Mesogenic Polyesters Using 1H Nuclear Magnetic Resonance Spectroscopy

Abstract A 1H NMR method has been used for the molecular weight determination of mesogenic polydecamethylene-4,4′-fumaroyldioxy-dibenzoates(P DFOB). Experimentally observed and empirically calculated chemical shifts for all non exchangeable protons are in good agreement. The number-average molecular weight has been calculated from the ratio of integral intensities OF resonances due to protons in the chain segments of the polymers to those from terminal protons. The correlation between molecular weight and intrinsic viscosity values is discussed. Results derived from NMR data are compared with those from other methods.

Orientational elastic deformations in polymer liquid crystals induced by electric fields: Aromatic polyesters

Abstract Elastic deformations induced by electric fields were investigated in nematic layers of two thermotropically mesogenic aromatic polyesters, with different structures of flexible spacers, and of their two low molecular weight analogues. It was shown by means of the polarizing microscopy that, in a planar-concave homeotropic layer of a nematic with negative dielectric anisotropy, bend deformation in the direction of an electric field and splay deformations in directions normal to it are induced by this field. The threshold electrical potentials of structural transitions and the values of dielectric anisotropy of these nematics were determined. For a polymer nematic with a diethylene glycol spacer, a dispersion and sign inversion of dielectric anisotropy was found in the range of radio frequencies. This phenomenon may be explained by the relaxation of the longitudinal components of the dipole moments of the mesogenic units of polymer chains.

Hydrodynamic, dynamo-optical and conformational characteristics of molecules of phenyl-substituted para-aromatic polyesters

Abstract Hydrodynamic, optical and conformational properties of mono-phenyl-substituted para -aromatic polyester (PAPE) in tetrachloroethane and dichloroacetic acid have been studied by sedimentation-diffusion analysis, viscometry and flow birefringence. The effect of phenyl side-groups on the equilibrium rigidity of PAPE chains was analysed. On the basis of these data, the energies of hindrance to intramolecular rotations about the ester bonds of various phenyl-substituted PAPEs were estimated.

Orientational elastic deformations of main-chain LC aromatic polyesters and low molecular weight nematics in a magnetic field

Abstract Orientational elastic deformations in a magnetic field were investigated in the nematic phase of polyphenylterephthaloyl-bis-(4-oxybiphenyl-4′-carbonyl), polylterephthaloyl-bis-(4-oxybiphenyl-3′-carbonyl), and their low molecular weight analogues. Temperature dependences of birefringence Δn were obtained and used to evaluate the degree of orientational order S. The splay and bend elasticiy constants, K1and K3, were determined. The elongation of the rigid mesogenic core in polymer molecules leads to an increase in the K3/K1 ratio, just as in the case of low molecular weight nematics. No effect of molecular weight on the values of Δn and Ki was detected.

Effects of orientation on the properties of liquid crystalline polymers

Abstract Mechanical properties and thermal behavior of liquid crystalline polymers with mesogene groups in the main chain were studied as functions of jet draw ratio. It is shown that tensile strength F and Youngs modulus E increase with draw ratio and the maximum E depends mainly on the chemical structure of chain and F is strongly affected by molecular packing that may be improved by heat treatment. The differential thermal analysis, thermal mechanical analysis and thermal acoustic analysis were used to find the spinning conditions for achieving maximum orientation and annealing conditions for macromolecular reconstructions without disorientation.