chapter  1
22 Pages

General Introduction on Dendrimers, Classical versus Accelerated Syntheses and Characterizations

Dendrimers are synthetically produced as monodispersepolymeric nanostructures with a tree-like, highly branched architecture. They are routinely synthesized as tunable “nanostructures” that may be designed and regulated as a functionof their size, shape, surface chemistry and interior void space. The word “dendron” is also encountered and accounts for “one branch” of the tree or one elementary building block which showsa functionality at its focal point.3,4 The first dendrimers published by Fritz Vögtle in 19782 were prepared via a divergent growth like those elaborated by R. G. Denkewalter at Allied Corporation in 1981,5 Donald Tomalia atDow Chemical Co. in 1983 and 19851,6 and George Newkome in1985.7 The convergent growth was later introduced, in 1990, byJean M. J. Fréchet.8Dendrimers are typically 2 to 20 nm in diameter and are composed of combinations of core types such as ethylene diamine (EDA), diaminobutyl (DAB), polyamidoamine (PAMAM),

polypropylimine (PPI). They also have different surface residues such as amine, carboxyl, and alcoholic groups to name but a few.Dendrimers can be divided in three distinct regions:the core, the interior (or branches), and the periphery (surface groups).A variety of dendrimers are available, and each has properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. The well-defined molecular compositions, sizes, and shapes of PAMAM dendrimers have also made them particularly attractive as (1) scaffolds for paramagnetic metal ions in magnetic resonance imaging and (2) templates for the synthesis of metal-bearing nanoparticles with tunable electronic, optical, catalytic, and biologic activity.Since the beginning of their history, hundreds of dendritic structures have been elaborated and among them Vögtle’s PPI, Tomalia’s polyamidoamine (PAMAM), Denkewalter’s poly(L-lysine) (PLL), Newkome’s polyamide, Grinstaff’s polyester (PGLSA-OH) and Hult’s poly(2,2-bis(hydroxymethyl)propionic acid (bis-MPA)) structures.9 These dendrimers are commercially available from providers like Dendritech Inc. (PAMAM), Frontier Scientific Inc. (Newkome’s polyamides), Colcom (poly(L-lysine)), Polymer Factory (bis-MPA), and DSM (PPI).10Dendrimers are often compared to their forebears, thepolymers, but they are never obtained by polymerization. Dendritic

structures can be divided into monodisperse dendrimers and dendrons (elementary unit) and polydisperse hyperbranched polymers, dendrigrafts and dendritic-linear hybrids such as dendronized polymers (Fig. 1.1).11