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

186 J. Roovers, B. Comanita
Scheme 4
convergent method lies in the decrease of the reactivity of the focal group which
is present at decreasingly lower concentration for higher generation dendrons.
Sixth generation dendrons have been prepared and coupled with a trifunctional
core to generate a dendrimer of 40,000 D [10].
The convergent method lends itself to accelerated growth. Fréchet et al. have
shown how a dendrimer with n end-standing functional groups can be used as
a core for reaction with n convergent dendrons each containing a reactive focal
group [11]. These are dendrimer-dendron reactions (Scheme 4). In this manner,
intermediate generations can be bypassed for an overall gain in time and yield.
Moreover, the double growth process allows the formation of radial block dendrimers
in one step because the core dendrimer and the peripheral dendrimer
can be of different chemical composition [11–13]. The limits of the double
growth process have been explored for the poly(benzyl ether) dendrimers [14,
15]. The results suggest that growth is not affected by steric crowding up to the
fifth generation. The double growth process has also been applied to the synthesis
of chiral dendrimers [16] and poly(phenylacetylene) dendrimer [17], as will
be discussed in Sect. 2.2.
This review does not attempt an exhaustive survey of the progress in the synthetic
chemistry of dendrimers. A number of reviews have already been dedicated
to this rapidly expanding subject [18–30].