Polyanion-polycation complex formation as a function of the position of the functional groups

Abstract

Abstract A method consisting of the combination of turbidimetry and conductometry was investigated to detect polyanion-polycation complex formation. We used ‘strong acid’ polyelectrolytes varying in charge density and ‘strong basic’ polyelectrolytes varying in the length of the spacer groups and in the accessibility of the quaternary ammonium function. Our systematic investigations have shown a predominantly 1:1 stoichiometry at the turbidimetric as well as the electrochemical titration endpoints. Deviations were observed when the individual components were significantly less soluble, i.e. when the polymers had units with long hydrophobic spacer groups and/or with quaternary ammonium functions that are sterically less accessible. Colloid stability as well as the type of turbidity curve are discussed on the basis of a two-step mechanism of symplex formation. The results are also compared with our earlier investigations. We previously found a general trend that a 1:1 stoichiometry could only be achieved with ‘strong’ polyelectrolyte components. Independently of the molar ratio of the cationic to anionic functional groups at the titration endpoint, the stability of the colloids of the symplex system was found to depend also on the molar mass, the charge density and the hydrophobicity of the comonomer units.