ABSTRACT
Dendrimers are nanomaterials having a well-defined and highly ordered branched structure. Most of the dendrimers known today are built from a multiplicative growth of branches emanating from a central polyfunctional core [1], as sketched in Figure 1. After successive steps of branching, a ball like structure evolves, the size of which cannot grow indefinitely due to the phenomenon of surface congestion, that is, of overcrowding of the terminal branches at the outer surface of the ball. The number of generations needed for congestion to set up depends on different geometrical parameters, namely, the multiplicity of the central core and of the branching sites, the branch length, and the cross-sectional area of the terminal groups. At the conges tion point, the dendrimers should be rather soft in their core and rigid in their outer surface [2,3]. Ball-like dendrimers are new materials appreciated for their potential technological applications: used as a dendritic box , their inner part may serve for carrying drugs [4,5]; covered with functional
Worm-like dendrimers are a recent field of interest and only a few kinds of materials have been synthesized up to the present time. The first example of such dendrimer reported in the literature [3] was made of polyethylenimine backbone bearing amidoamine dendrons (Figure 4a). Further examples were made of arylether and arylamide dendrons attached onto a variety of backbones such as polystyrene, polymethacrylate, poly(meth)acrylamide, or polyphenylene (Figure 4b and c). Steric hindrance is one major difficulty in the synthesis of dendrimers, especially when high generation orders with high molecular weight backbones are sought after. For instance, in the case of the dendrimer presented in Figure 4b, only oligomers (DP~7) could be prepared at second generation order [11]. To get higher DPs at higher generation orders, one should release steric hindrance by either lengthening
and flexible polymer backbones and branches, we wished to verify whether it is possible to obtain rigidification of the polymer backbones simply through congestion. On the other hand, by using short branches, we expected to reach congestion at a low generation order so as to gain mech anical rigidity and, hopefully, to induce formation of liquid crystals.
