Peter N. Lavrenko

On the separation ability of various ficoll gradient solutions in zonal centrifugation

Ficoll samples of various molecular weights, Mr(15-4200) X 10(3), forming gradient solutions with different separation resolutions and a more selective action have been obtained by fractionation of Ficoll 400 polysaccharide. On the basis of sedimentation-diffusion data and viscometry of Ficoll fractions in water and dimethylformamide, conclusions about the type of branching of macromolecules and the intensity of intramolecular hydrodynamic interaction were made; the size and shape asymmetry of Ficoll molecules were calculated in connection with their mobility in solution.

Conformation of carboxymethylcellulose in cadoxen-water solutions

Abstract Diffusion, sedimentation and viscosity of carboxymethylcellulose (CMC) (DS = 0.9 ±0.1, 28 000 ⩽ m ⩽ 380 000) were studied in cadoxen-water systems over a wide range of solvent composition. The results were interpreted according to the theory of hydrodynamic properties of worm-like chains. The equilibrium rigidity of CMC in cadoxen-water was shown to be comparable to that of unsubstituted cellulose in the same solvent. On dilution of the cadoxen-CMC system with water, no charge effects became visible up to a dilution ratio of 10 parts by weight of water per 1 part by weight of cadoxen, but the equilibrium rigidity increased considerably. The conformational parameters of CMC were compared to those of other cellulose derivatives and some synthetic polymers.

Hydrodynamic and dynamo-optical properties and conformation of cyanoethyl cellulose molecules in solution

Translational diffusion, velocity sedimentation and viscosity in acetone as well as flow birefringence (FB) and viscosity in cyclohexanone have been investigated for cyanoethyl cellulose (CEC) with degree of substitution 2.6 in the range of M = (24.5−317) × 103. The dependences of [ν], So and Do on M were obtained. The value of the hydrodynamic constant is A0 = 3.27 × 10−10erg deg−1mol−13. According to hydrodynamic data, the equilibrium rigidity of CEC molecules is characterized by the length of the Kuhn segment A = 240 − 350 A and the coefficient of hindrance to intramolecular motion σ = 4.5-5.4. The hydrodynamic diameter of the chain is 8–14 A. According to the FB data, the value of A is 260 A. This value is in agreement with hydrodynamic data. The high value of optical anisotropy of the monomer unit, a| - a⊥ = 17.8 × 10−25 cm3, is in agreement with the structure and anisotropy of the substituting groups, and the investigation of orientation angles of FB leads to the conclusion that, apart from high equilibrium rigidity, CEC in solution is characterized by considerable kinetic chain flexibility. The data for CEC are compared with the characteristics of other cellulose esters and ethers.

Electric birefringence in solutions of cellulose carbanilate as a function of molecular weight

Abstract Electro-optical, dynamo-optical and hydrodynamic properties of solutions of some fractions of cellulose carbanilate (CC) in dioxan have been investigated. In a variable electric field, strong dispersion of the Kerr effect is observed, indicating the dipole-orientational mechanism of electrical birefringence and its relaxation. A comparison of relaxation times of fractions with their molecular weights and intrinsic viscosities indicates that the mechanism responsible for the Kerr effect is the rotation of the molecule as a whole in an electric field (a kinetically rigid molecule). The dependence of relaxation time on molecular weight (M) shows that, with increase in M, the conformation of the CC molecule changes from a slightly curved rod to a rigid Gaussian coil. The same conclusion may be drawn from a study on the dependence of the equilibrium value of the Kerr constant on M. In the Gaussian range (high M), the Kerr effect depends on the longitudinal (with respect to the chain) component of the dipole moment formed by the CO bonds in the glucoside ring. At low M, the transverse components of the monomer dipoles begin to play an important part in birefringence.

A new approach to calculating the molecular draining effect from sedimentation and diffusional data

Abstract Treatment of experimental dependence of the translational friction coefficient on molecular weight, f(M) , obtained for semi-flexible macromolecules, is discussed. A draining effect is significant for these chains and must be taken into account to determine the correct values of unperturbed dimensions of the macromolecule. For this purpose a new relation between the Flory factor P and the scaling exponent b (in the equation f = K f M b ) has been proposed. According to the Yamakawa theory developed for translational friction of the wormlike chains, the relation is valid for macromolecules with any length exceeding two times the statistical segment length, and with any diameter. The method has been applied to hydrodynamic properties of poly(chlorohexyl isocyanate) in carbon tetrachloride.

Shift interferometry in analytical ultracentrifugation of polymer solutions

The polarized-light interference method is applied to visualize a distribution of macromolecule concentrations based on displacements in an ultracentrifugal cell. The optical system based on the Lebedev interferometer is presented. The sensitivity and precision of the system are compared with those of the widely used Schlieren optical system and Rayleigh interference optics when applied to synthetic polymer dilute solutions. Some questions of methodology are discussed.

Conformational and dynamo-optical properties of fluorinated poly(p-phenylene-1,3,4-oxadiazole-imide-amide) molecules in solutions

Abstract Conformational parameters of the fluorinated poly( p -phenylene-1,3,4-oxadiazole-imide-amide) molecules in dilute solutions in N , N ′-dimethylacetamide, N , N ′-dimethylformamide and 96% sulphuric acid were evaluated by using the data of hydrodynamic and dynamo-optical investigations. Optical anisotropy of the statistical Kuhn segment was found to be about half of that for poly(amide-benzimidazole) and close to that previously obtained for poly( p -phenylene-1,3,4-oxadiazole) molecules. The observed effect is referred to the higher equilibrium flexibility of the polymer chain attributed to the hexafluoroisopropylidene units incorporated into the molecule backbone. Noticeable degradation of the polymer molecules in solution in 96% H 2 SO 4 at ambient temperature was detected and characterised.

Stability and degradation of poly(1,4-phenylene-1,3,4-oxadiazole) molecules in sulphuric acid

Abstract The translational diffusion coefficient and intrinsic viscosity of poly(1,4-phenylene-1,3,4-oxadiazole) molecules in 96% H 2 SO 4 have been determined at different stages of degradation of the molecules in acid solution at temperature ranging from 82 to 105 °C. The degradation rate constant, k , has been obtained from the change in the molecular weight, M , of the product degraded in solution with time at high temperature. The activation energy of the hydrolysis process was 103 ± 7 kJ mol −1 , which is smaller than that of aromatic polyamides in the same solvent. According to our hydrodynamic data, the degree of coiling of the molecules of degraded products does not differ from that of undegraded samples, and our conclusion was that the degradation is not accompanied with a noticeable change in the short-range interactions in the molecular chain and may be understood as a random chain scission.

Conformational properties of poly-p-phenylene-1,3,4-oxadiazole molecules in sulphuric acid

Hydrodynamic and dynamo-optical properties of samples of poly-p-phenylene-1,3,4-oxadiazole (POD) with molecular weights from 4.6 × 103 to 100 × 103 in dilute solution in 96 and 100% sulphuric acid have been investigated. Molecular-weight dependence of intrinsic viscosity for POD in 96% H2SO4 was established by light scattering and viscometry methods as [η]96=Mw2(52 + 0.77 × Mw12)−3. Weak charge effects were detected in the diffusion phenomenon of POD molecules in 100% H2SO4. The data on flow birefringence and diffusion-viscometric analysis show the absence of aggregation of POD molecules in 100% H2SO4 and increase in the degree of expansion of the POD molecules in solution with increasing H2SO4 concentration up to 100%. This increase is equivalent to an increase of several times in the Kuhn segment length. The possible causes of this effect are discussed.

Synthesis and Molecular Properties of New Side-Chain Liquid Crystalline Polymers Based on the Baylis-Hillman Reaction

Abstract A new methodology has been employed in synthesis of two side-chain liquid-crystalline polymers with cyanobiphenylene mesogenic groups and variation of -CN, -COCH3 and -OH groups displacement in the backbone surrounding. Hydrodynamic and electrooptical (the Kerr effect) methods were used to study their molecular properties in solution in benzene and chloroform. Electrooptical properties of polymers are compared with the same ones of homologous series of alkoxycyanobiphenylenes as the model compounds of the polymer mesogenic groups. Different mobility of the side-chain mesogenic groups in polymers under investigation was observed and related to the chemical and dipole structure.