S.S. Skorokhodov

Synthesis of high-molecular weight liquid crystal polyesters based on a polycondensation mesogenic monomer☆

Abstract This paper relates to the scheme proposed for the synthesis of high-molecular weight alkylene aromatic polyesters capable of forming liquid-crystal melts. This is the first time that the mesogenic dichloride, terephthaloyl-bis-(4-oxybenzoyl chloride) has been separated and characterized. Polycondensation of this diacidchloride with various aliphatic and hydroxyaliphatic diols resulted in polymers with temperatures of transition to the liquid-crystal state in the interval from 40 to 360°. The procedure and conditions of polycondensation were selected, taking as an example the synthesis of a single polymer, polydecamethyleneterephthaloyl-bis-(4-oxybenzoate). Relations between phase transition temperatures and MW have been investigated for this polymer.

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.

Investigation of polymerization and copolymerization of 9-vinyl-anthracenes

Abstract The processes accompanying homopolymerization and copolymerization of 9-vinyl-anthracene (9-VA) and 9,10-vinyl-10-methyl-anthracene (9,10-VMA) were investigated. It was shown by electronic spectra that free-radical copolymerization of 9-VA and 9,10-VMA with methyl methacrylate yielded copolymers containing units of 9-methylene-9,10-dihydroanthracene structure. Acidic treatment of the copolymer solutions led to rearrangement of these units into 9,10-dialkylanthracene units incorporated into the main chain of the macromolecule. The position of anthracene-containing units in the chains was determined from fluorescence data. Free-radical isomerization copolymerization of 9-vinyl-anthracenes was used for obtaining model polymers with fluorescent marks incorporated into the backbone. These polymers are necessary for investigating intramolecular motion of macromolecules by the method of polarization of fluorescence.

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.

Features of the conformational state of polyesters with mesogenic groups and flexible spacers within the main chain

Conformational changes and variations in intermolecular ordering have been investigated for polydecamethyleneterephthaloyl-di-oxybenzoate in various physical states, including the partially crystalline, liquid-crystalline and the isotropic melt. The investigation was based on IR-spectroscopy and polarization microscopy. Transitions from the partially crystalline state to the liquid-crystalline is accompanied by changes occurring in mesogenic as well as in flexible portions of the molecule: in the former portion the mutual placement of benzene rings and ester groups is altered; in the latter it was found that long trans-trans-sequences disappear, and the number of gauche isomers in methylene spacers is increased. Transition from liquid crystalline melt to the isotropic one is not actually accompanied by conformational changes, but is characterized by a redistribution of gauche-trans isomers along the chain, which influences the intermolecular order and the extent of the ordered regions.

Conformational characteristics of para-aromatic polyester molecules as shown by diffUSAion, viscometry and flow birefringence of their solutions☆

Translational diffUSAion, viscometry and f.b.r. have been USAed to study the hydrodynamic and optical properties of a p-aromatic polyester of different MW in dichloroacetic acid. It is shown that the polyester macromolecules display in the f.b.r. phenomenon properties of kinetically rigid worm-like chains and are characterized by the parameter of equilibrium rigidity-length of the Kuhn segment A = (380 ±50) A, the factor of braking of internal rotation σ=1·1 and the anisotropy of the chain unit length β=8·6×10−17 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.

The determination of orientational order in liquid crystalline melts of polydecamethlyne terephthaloyl-dioyxbenzoate☆

Abstract Methods are proposed for determining orientational order, using IR-spectroscopy with polarized radiation. It has been shown that the degree of orientational ordering of main chain mesogenic groups in liquid crystalline polymer melts is 0·5–0·6. The values obtained are close to those for low molecular weight nematic melts.

Molecular properties and phase conditions of polymers with mesogenic groups in the main chain

Abstract A study was made of molecular properties and phase conditions of polydecamethylene terephthaloyl di- p -oxybenzoate containing mesogenic groups in the main chain. It was shown that this polymer in melt changes into the liquid-crystalline state with the formation of a defective laminated structure.