G. E. Polushina

Molecular Properties of the Copolymers of N,N-Diallyl-N,N-Dimethylammonium Chloride and Maleic Acid

The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied. For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes. In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm. The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along the chain contour.

Molecular properties of poly(carboxybetaine) in solutions with different ionic strengths and pH values

Viscometry and dynamic and static light scattering are employed to study the molecular properties of water-soluble poly(carboxybetaine), that is, poly(2-(diallyl(methyl)ammonium) acetate). It is shown that, in solutions with pH 1, the polymer behaves as a polyelectrolyte. In media with pH 6 and 13, an increase in the concentration of sodium chloride increases the intrinsic viscosity of the polymer and the hydrodynamic radius of its macromolecules, thereby indicating the antipolyelectrolyte effect typical of polymer zwitterions. In water and 0.1 M NaOH, the second virial coefficient of the polymer is close to zero, while exponent ν, which relates the sizes of macromolecules to their molecular masses, is 0.5. In 1 M NaCl, the second virial coefficient becomes positive, while exponent increases to 0.58. The Kuhn segment lengths of poly(carboxybetaine) molecules are 6.3 and 6.6 nm in water and 1 M NaCl, respectively. An increase in the hydrodynamic radius of macromolecules with the ionic strength of the solution is due to the shielding of attraction between zwitterions belonging to polybetaine monomer units located far apart along a macromolecular chain.

Hydrodynamic and conformational properties of dendron-modified polystyrene molecules

The molecular characteristics of polystyrene modified by the Frechet type dendrons of 1–4 generations were studied in tetrahydrofuran by viscometry, isothermal diffusion, electric birefringence, and dynamic and static light scattering. It was shown that dendronized polystyrene molecules whose polymerization degree changes from 1640 to 930 with an increase in the generation number of dendrons occur in the coillike conformation. The equilibrium rigidity of macromolecules tends to increase with increasing the generation number of dendrons. The Kuhn segment length grows from 3.9 nm for polystyrene molecules modified by dendrons of the first generation to 23.3 nm for polystyrene molecules carrying dendrons of the fourth generation.

Electrical and dynamooptical properties of Frechet dendron-modified polystyrene molecules in solutions

The electrooptical, dynamic, and dielectric characteristics of polystyrene modified by the Frechet dendrons of 1–4 generations have been studied in benzene, chloroform, and THF solutions. It has been shown that the Kerr constant and the shear optical coefficient for all the studied polymers coincide in sign and their absolute values increase with the dendron generation number. The intrinsic optical anisotropy of the repeating unit of dendronized polystyrene molecules is negative in sign, and its absolute value tends to grow with an increase in the generation number of dendrons. The frequency dispersions of the Kerr constand and of the dielectric polarization have been discovered for solutions of the modified polymer. The ratio between the times of relaxation characterizing the dispersion of dielectric permittivity and of the Kerr constant of solutions and the times of a rise and decay of electric birefringence measured on the onset and termination of the rectangular-pulsed field does not obey the longitudinal relaxation theory for polar macromolecules. The relaxation times of dielectric polarization and of electric birefringence tend to increase with the dendron generation number.

Water-soluble polyelectrolyte complexes of pyridine-containing polyphenylene dendrimers

The sizes of soluble polyelectrolyte complexes formed through mixing of solutions of dimethyl sulfate-alkylated rigid pyridine-containing polyphenylene dendrimers of various generations with the solution of sodium polystyrenesulfonate are measured with the use of dynamic light scattering. Effects of the length of the polyanion chain of the dendrimer, the generation number of the dendrimer, and the charge ratio of polymer components on the sizes of the complexes are examined. The results of this study are in agreement with the theoretical analysis of interaction between the charged dendrimer and the polyelectrolyte of the opposite charge sign and suggest the spontaneous formation of nanosized particles of water-soluble complexes.

Electro-optics of solutions of biopolymers and their complexes

The review summarizes the results of electric-birefringence studies of the molecular properties of biopolymers and their complexes. The application of alternating electric fields makes it possible to study the kinetics of orientation of DNA, RNA, and polypeptide molecules in diluted solutions. An analysis of molecular-mass dependences of relaxation times of biopolymer molecules in terms of the rotational friction theory is used to determine the equilibrium rigidity of macromolecules characterized by Kuhn segment length A. For DNA molecules in buffer solutions with a low ionic strength, the value of A derived from electro-optical measurements is 114 nm. The high sensitivity of electric birefringence to changes in the secondary and tertiary structures of biopolymers ensures its use for the analysis of sequence curvature in short fragments of DNA and for investigation of transitions between different tertiary structures of RNA. The study of electro-optical birefringence in solutions of complexes of DNA and polypeptides with oppositely charged ions of surfactants makes it possible to gain insight into their conformational properties in organic solvents. The stoichiometric complexes of DNA in chloroform occur in the compact globular state, whereas the conformation of complexes formed by various polypeptides depends on their composition and may vary from rodlike to coiled. Electric birefringence in solutions of biopolymer complexes is associated with the orientation of molecules that is due to the external-field-induced dipole moment that appears as a result of a small displacement of ions along the contour of polyion chains. The time of reaching the induced dipole moment is equal to or greater than the time of orientational relaxation of the complex as a whole.

Electroptical and dynamic properties of sulfonated polystyrene molecules and their associates in chloroform

The behavior of sulfonated PS containing 0.5, 1.35, 2.6, and 5.8 mol % of sodium sulfonate groups in chloroform solutions has been studied by static and dynamic light scattering, viscometry, and electric birefringence. The molecular mass of ionomers is measured, and their translational diffusion coefficient, intrinsic viscosity, and free relaxation times are estimated. It has been shown that association in solutions of ionomers containing more than 1.35 mol % of sodium sulfonate groups proceeds according to the open association model. Analysis of autocorrelation functions of scattered light intensity and electric birefringence decay makes it possible to determine translational diffusion coefficients and relaxation times for individual ionomer molecules, their pair associates, and higher multiplicity associates. With an increase in the fraction of sodium sulfonate groups, the hydrodynamic radius of individual ionomer molecules decreases from 8 to 5.8 nm, while the ratio between the hydrodynamic radius of pair associates and individual sulfonated PS molecules increases.

Molecular and Conformational Properties of Dendronized Polymethacrylate in Organic Solvent

The conformational and dynamo-optical properties of a homologous series of polymethacrylate modified by first-generation Fréchet-type dendrons in the molecular mass range of 70–8800 kDa in organic solvents were studied by viscometry, isothermal diffusion, dynamic light scattering, and flow birefringence. The Mark-Kuhn-Houwink equations for this dendronized polymer in toluene and chloroform together with hydrodynamic diameter and Kuhn segment length in toluene are defined as well as the value of intrinsic anisotropy of polarizability for the monomer unit.