Complex formation by electrostatic interaction between carboxyl-terminateddendrimers and oppositely charged polyelectrolytes

yComplex formation between a carboxyl-terminated cascade polymer (generatio n 3) and several cationic polyelectrolytes of varying linear charge density was studied as a function of ionic strength, by turbidimetric titration an d dynamic light scattering. Tetramethylammonium chloride was used to adjust the ionic strength in order to avoid sodium counterion binding to dendrime r carboxyl groups. Complex formation occurred abruptly at a critical pH, as signaled by a sudden change in either the turbidity or the apparent Stokes radius from dynamic light scattering. The pH(c) of incipient complex forma tion was converted to the critical surface charge density sigma(c). Under c onditions of low or moderate ionic strength (I), it was confirmed that sigm a(c) is roughly proportional to kappa/xi, where kappa similar to I-1/2 is t he Debye-Huckel parameter and xi is the linear charge density of the polyel ectrolyte.