POLYANION-POLYCATION COMPLEX-FORMATION AS A FUNCTION OF THE POSITION OF THE FUNCTIONAL-GROUPS

A method consisting of the combination of turbidimetry and conductomet ry 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 gro ups 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 endpoin ts. Deviations were observed when the individual components were signi ficantly less soluble, i.e. when the polymers had units with long hydr ophobic spacer groups and/or with quaternary ammonium functions that a re sterically less accessible. Colloid stability as well as the type o f turbidity curve are discussed on the basis of a two-step mechanism o f symplex formation. The results are also compared with our earlier in vestigations. We previously found a general trend that a 1:1 stoichiom etry 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 th e symplex system was found to depend also on the molar mass, the charg e density and the hydrophobicity of the comonomer units. Copy (C) 1996 Elsevier Science Ltd.