Sizes and conformations of hydrophilic and hydrophobic polyelectrolytes in solutions of various ionic strengths

The hydrodynamic characteristics of macromolecules of a random copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride containing 43.6% charged units in the molecular-mass range of 27 × 103 to 355 × 103 are studied. For solutions in 0.2 M NaCl, sedimentation and translational-diffusion coefficients are determined. For salt-free solutions and for solutions in 0.2 and 5.0 M NaCl, the intrinsic viscosities of the fractions are found. The lengths of the statistical segments of the chains are estimated in terms of the Gray-Bloomfield-Hearst theory. The behavior of the polycation, whose uncharged counterpart is a hydrophilic polymer, is compared to the behavior of poly(sodium 4-styrenesulfonate), whose uncharged counterpart is a hydrophobic polymer. The comparison is based on normalized scaling relations. It is shown that the level of compaction of macromolecules of strong polyelectrolytes at a high ionic strength is determined by the degree of hydrophobicity of their polymer chains. Polyelectrolytes based on hydrophilic polymers cannot be compacted into a preglobular state; their chains preserve a swollen coil conformation up to maximally high values of ionic strength.