Fractions of the copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride containing 15.7 ± 0.5% of charged units are obtained by radical polymerization, fractionation, and hydrolysis. Viscous flow, velocity sedimentation, and translational diffusion of their dilute solutions are studied in 0.2 M NaCl. Viscosimetric studies are also carried out in a wide range of ionic forces: from the minimum (~10^–6 mol/L) to the maximum (6 mol/L). The hydrodynamic volumes and equilibrium rigidity of the copolymer under study are compared with the data obtained earlier for an uncharged homopolymer and a copolymer with a higher linear charge density (~44% of charged units) in solutions with different ionic strength. The correspondence of the values obtained to the theories of Odijk, Skolnik, and Fixman (OSF) as well as Dobrynin is discussed.

The peculiarities of viscosity data treatment for two series of polymer systems exhibiting associative properties: brush-like amphiphilic copolymers—charged alkylated N-methyl-N-vinylacetamide and N-methyl-N-vinylamine copolymer (MVAA-co-MVAC_nH_2n+1) and charged chains of sodium polystyrene-4-sulfonate (PSSNa) in large-scale molecular masses (MM) and in extreme-scale of the ionic strength of solutions were considered in this study. The interest in amphiphilic macromolecular systems is explained by the fact that they are considered as micellar-forming structures in aqueous solutions, and these structures are able to carry hydrophobic biologically active compounds. In the case of appearing the hydrophobic interactions, attention was paid to discussing convenient ways to extract the correct value of intrinsic viscosity $\left[\eta \right]$ from the combined analysis of Kraemer and Huggins plots, which were considered as twin plots. Systems and situations were demonstrated where intrachain hydrophobic interactions occurred. The obtained data were discussed in terms of $\ln {\eta }_{\mathrm{r}}$ vs. $c\left[\eta \right]$ plots as well as in terms of normalized scaling relationships where ${\eta }_{\mathrm{r}}$ was the relative viscosity of the polymer solution. The first plot allowed for the detection and calibration of hydrophobic interactions in polymer chains, while the second plot allowed for the monitoring of the change in the size of charged chains depending on the ionic strength of 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, l_qq/A_bare, describing this behavior was proposed (l_qq is the average distance between the neighboring charges along the chain, and A_bare 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].

An experimental tool for the evaluation of intramolecular associative/hydrophobic interactions in polymer/solvent systems was proposed and tested. The method is based on the measurements of the viscous flow in dilute polymer solutions and the analysis of the ln η_rvs. c[η] dependence. This second derivative has a positive sign in the case of associating polymer or copolymer systems, and is negative for the non-associating ones. The value of the second derivative of this dependence may be used as a measure of the solvophobicity of polymer systems. Results obtained for three polymer systems: comb-like amphiphilic copolymers of N-methyl-N-vinyl acetamide and N-methyl-N-vinyl amine, brush-like copolymers of styrene and methyl methacrylate, and linear polystyrene, are presented and discussed.