Effect of charge density on the formation and salt stability of polyelectrolyte complexes
Cationic copolymers of diallyldimethylammonium chloride (DADMAC) and N-methyl-N-vinylacetamide (NMVA) were synthesized by radical polymerization in a broad range of composition. Since the cyclocopolymerization of DADMAC and NMVA proceeded as nearly ideal reaction, linear copolymers of different charge densities but approximately equal molecular weights and acceptable polydispersities could be obtained. These polycations were used in combination with a sodium poly(styrene sulfonate) to study the effect of charge density on the course of poly-electrolyte complex (PEC) formation and the response of the PECs to subsequent addition of salt. Static light scattering was employed for the characterization of the complex structures. PEC formation followed in deionized water for all copolymers the same scheme, but yielding higher swollen particles with decreasing charge density of the polycations. In the cases of stronger mismatching of the charge densities of the components the presence of NaCl during complex formation led to highly swollen complexes on a very low level of aggregation. Subsequent addition of NaCl resulted for these polyelectrolyte combinations at first in disintegration into very small subunits before flocculation occurred.