Relaxation of copolymeric dendrimers built from alternating monomers

In this study we extend our previous work concerning the Rouse dynamics of linear alternating copolymers (Macromolecules 2003, 36, 486) to tree-like structures and focus on copolymeric dendrimers built from monomers of two kinds A and B; as before, we let the monomers differ in their interaction with the solvent. In the framework of generalized Gaussian structures (GGS), we consider alternating arrangements of monomers over the dendritic structures. We develop a semi-analytical method to determine for such structures (of arbitrary functionality, f, and number of generations, g), the eigenfrequencies (relaxation times). The method allows us to compute readily the storage, [G′(ω)] and the loss, [G″(ω)] moduli. These quantities show a multitude of features which mainly depend on the difference in the mobilities, or, equivalently, in the friction coefficients ζA and ζB of the A- and B-beads. These features range from the presence of large plateau-type regions in [G′(ω)] to the appearance of double-peaks in [G″(ω)]. In contrast to linear alternating copolymers, the behavior of the dynamic moduli of copolymeric systems with dendritic topology can shed light into their composition, i.e. into the relative numbers of A- and B-beads. We discuss these aspects in view of their experimental relevance.