142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

Dendrimers and Dendrimer-Polymer Hybrids 181
Rg radius of gyration
Rh
Rh SEC
hydrodynamic radius from intrinsic viscosity
hydrodynanic radius from translational diffusion coefficient
size exclusion chromatography
TEMPO 2,2,6,6-tetramethylpiperidine oxide
Ve elution volume
[ h] intrinsic viscosity
Q scattering angle
l wavelength of radiation
n scaling exponent
sc chromatographic dispersion due to the instrument
sd chromatographic dispersion due to sample polydispersity
total chromatographic dispersion
s T
1
Introduction
1.1
Dendritic Architecture
Dendrimers are molecules with regularly placed branched repeat units. They are
also known as Starburst, Cascade or Arborols. These names describe aspects of
their molecular architecture. Dendrimers consist of different parts (see Fig. 1).
Each dendrimer has a core or focal point. The core is the central unit of the dendrimer
and can formally be regarded as the center of symmetry for the entire
molecule. The core has its characteristic branching functionality, i.e. the
number of chemical bond by which it is connected to the rest of the molecule
(Fig. 1a). The focal point plays the same role as the core. Moreover, it has a chemical
functional group not found elsewhere in the dendrimer.
Attached to the core or focal point is a first layer of branched repeat units or
monomers (Fig. 1b). This layer is alternatively considered to be the zeroed or
first generation of the dendrimer. Each successive generation is end-standingly
placed onto the previous generation (Fig. 1c). Each generation usually but not
necessarily contains the same branched repeat units. The process of growth is
extendable to several more generations. Because of the multifunctionality of
each repeat unit, the number of segments in each generation grows exponentially.
The end-standing groups of the outermost generation are called peripheral or
terminal groups.
The description of dendrimers as outlined suggests that there is a fixed spacial
arrangement in dendrimers whereby the core or focal group forms the center,
successive generations radiate outwardly, and end-groups of the outermost
generation form an outer surface. This is only partly true. A dendrimer is indeed
a framework of chemical bonds and bond angles between atoms that vary little;
however, the torsion angles about the s bonds allow for a wide range of conformations
and numerous dynamic transitions between them. Therefore, the core