The viscosity law of dendronized linear polymers.

The intrinsic viscosity [η] of dendronized linear macromolecules dissolved in thermodynamically good solvents depends both on chain length that is contour length L(c) of the backbone of the polymer and on the persistence length l(p). Investigating a set of samples of identical L(c) but differing in the generation number for which data on lp are available, it becomes possible to establish a generalized viscosity law in the form [η] = K(M/M(p))(α) in which M(p) denotes the molar mass of the objects per l(p), M is the total molar mass, K is a constant, and α is the Mark-Howink exponent, which is found to be 0.55.

Dendrimer influenced supramolecular structure formation of block copolymers: II. Dendrimer concentration dependence.

The dendrimer concentration dependence of the supramolecular structure formation of polystyrene-block-poly(acrylic acid) in dioxane/THF was investigated as a function of water content. The distribution as well as the localization of the dendrimer units inside the formed aggregates were determined by comparative studies of turbidity measurements and transmission electron microscopy. The strong and specific interactions present between the amine groups of the dendrimer (PAMAM) and the carboxylic acid residues of PAA in the copolymer have a strong influence on the structure formation. The PAMAM concentration as well as the character of the terminal groups of the dendrimer influence the strength of these interactions and consequently affect the structure formation process. As shown by fluorescence quenching experiments, on all supramolecular hierarchical structure levels, and specifically in vesicles, the dendrimer is coated by the PAA chains of the block copolymer due to the strong interactions; since the PAA blocks are connected to the PS blocks, which form the corona, the dendrimer is surrounded by PS chains and is thus encapsulated into the hydrophobic regions of the block copolymer aggregates. A high-resolution transmission electron microscopy image of a micelle is shown, in which the individual dendrimer cores are seen to be localized in the center of these aggregates, and thus, the structure proposed in the previous publication (Kroeger, A.; Li, X.; Eisenberg, A. Langmuir 2007, 23, 10732) is confirmed. Furthermore, the sizes of the resulting aggregates depend on the relative concentration of dendrimer, expressed as RAm/Ac (the ratio of amine to acid groups). With increasing RAm/Ac values, not only the sizes of the micelles but also the vesicle dimensions, especially vesicle wall thicknesses, increase, and this effect suggests the encapsulation of the dendrimer into the vesicle walls. Thus, the constitution of the vesicle structure is determined precisely. This feature allows the potential incorporation of a wide range of species into the vesicle walls or the center of the micelle cores.