Spectrum of hydrodynamic volumes and sizes of macromolecules of linear polyelectrolytes versus their charge density in salt-free aqueous solutions.

Molecular characteristics of statistical copolymers based on hydrophilic poly(N-methyl-N-vinylacetamide) have been monitored throughout the entire possible range of charge density from 1.5 to 39 mol%. Different trends in the dependence of intrinsic viscosity on the average charge density of polymer chains at minimal ionic strength were revealed. A new parameter, lqq/Abare, describing this behavior was proposed (lqq is the average distance between the neighboring charges along the chain, and Abare is the statistical segment length of a non-charged homologue). For polyelectrolyte chains, this parameter allows the regions of charge density values where electrostatic long-range or short-range interactions dominate to be indicated. Two homologous series of copolymers were characterized by methods of molecular hydrodynamics under conditions of suppressed charge effects. Intrinsic viscosity in salt-free solutions characterizing an individual macromolecule was estimated by a method proposed earlier [Pavlov et al., Russ. J. Appl. Chem., 2006, 79, 1407-1412].

O,N-(2-sulfoethyl)chitosan: Synthesis and properties of solutions and films.

A series of water-soluble sulfoethylated chitosans (SEC) with degrees of substitution (DS) up to 130% were obtained using a heterogeneous reaction of chitosan with sodium 2-chloroethanesulfonate in 85% isopropanol in the presence of NaOH. NMR and FTIR spectroscopy confirmed that sulfoethylation of chitosan preferentially happens at hydroxyl groups and to some extent at amino groups, giving mixed substituted O,N-SEC. Chitosan shows positive birefringence, whereas SEC shows negative values, indicating self-organization in dilute solution. Dynamic light scattering studies revealed the presence of aggregates in dilute solutions of chitosan and SEC. The sizes of the SEC aggregates are sensitive to the DS and the nature of the solvent. X-ray diffraction of SEC films revealed that the introduction of sulfoethyl groups into chitosan leads to amorphization, which is more pronounced at higher DS. During the storage of SEC films, the samples loose solubility due to the formation of ionic crosslinks upon dehydration.

Conformation parameters of linear macromolecules from velocity sedimentation and other hydrodynamic methods.

Linear macromolecules constitute a broad class of synthetic and natural polymers which are highly useful in various technologies and represent the key molecular systems in living nature. The study of the molecular characteristics of these polymers represents an important problem in fundamental and applied science. The methods of molecular hydrodynamics have been and remain an important way of studying the molar mass, molar mass distribution, size and conformation of linear polymers. This paper discusses the approaches to the problems of hydrodynamic methods, in particular analytical velocity ultracentrifugation, in the study of various types of linear macromolecule. The velocity sedimentation data were processed with three different methods: Sedanal and Sedfit software, and the classical approach of evaluating the rate at which the sedimentation boundary moves. The Sedfit program also allows an evaluation of the frictional ratio values, i.e., the coefficient of translational diffusion. It will be discussed for which systems the estimation of the frictional ratio obtained by Sedfit is adequate and for which it is not. The applications of other hydrodynamic methods (intrinsic viscosity, translational diffusion) are also discussed with a view to obtaining the conformational characteristics of linear macromolecules.

Conformational parameters of poly(N-methyl-N-vinylacetamide) molecules through the hydrodynamic characteristics studies.

Water-soluble PMVA was synthesized by radical polymerization methods. A number of polymer samples were fractionated in the chloroform-diethyl ether system. Fractions were studied by molecular hydrodynamics methods (sedimentation velocity, translational isothermal diffusion and viscosity) in H(2)O and DMF. The molecular masses of fractions were determined and the Kuhn-Mark-Houwink-Sakurada relationships were obtained in the molecular mass range of 3.5 < M x 10(-3) g x mol(-1) <540. A negative temperature coefficient of the characteristic viscosity was obtained in both solvents. The Kuhn statistic segment length and the hydrodynamic diameter of the molecule were estimated for PMVA. The hydrodynamic volumes, occupied by the molecules of PMVA, poly(1-vinyl-2-pyrrolidone), poly(vinylformamide), and pullulan were compared.