Chouai and Simanek
resonance imaging,9 materials and coatings,10 sensors and
detectors,11 catalysis,12 and separations.13 The allure of these
materials is apparent in their depiction: dendrimers are mono-
disperse, polyfunctional polymers whose shape, size, topology,
flexibility, and molecular weight can be controlled during
preparation.14
Still, dendrimer synthesis remains a challenge. Obstacles to
producing large quantities of pure compounds can be magnified
by the need for sophisticated and/or sensitive building blocks,
nontrivial isolation strategies, and the requirement for expensive
and/or excess reagents. In the extreme, either convergent or
divergent approaches can be applied.1,3,14,19 In the divergent
approach, the dendrimer is assembled from the central core.
Growth of successive generations requires that more reactions
be executed as the synthesis progresses. This approach-when
executed with perfect efficiency-leads to mole conservation.
That is, the number of moles of product is reflected in the
number of moles of core that are initially employed. Mass is
incrementally added throughout the course of the synthesis. The
convergent method relies on building the dendrimer from the
surface inward toward the core. Commonly, surface groups are
repeatedly dimerized leading to larger dendrons that finally
attached to a central core. The number of moles of product are
a fraction (indeed, an exponentially unfavorable fraction) of the
moles of surface groups initially available. A majority of the
mass is carried throughout the synthesis. Yet, this strategy has
as a primary advantage that only a limited number of reactions
are performed at each generation. A variety of new dendrimers
have been reported using both divergent and convergent methods
that incorporate a wide range of functionalities such as ethers,20
amides,21 esters,22 alkynes,23 carbonates,24 saccharides,25 gly-
copeptides,26 and siloxides.27
Our interest in dendrimers based on 1,3,5-triazine derives in
part from the availability and low cost of 2,4,6-trichloro-1,3,5-
triazine (cyanuric chloride), the core reagent. The ease of
displacement of chlorine atoms of cyanuric chloride by different
amine nucleophiles to generate mono-, di-, and trisubstituted
1,3,5-triazines makes its adoption even more attractive.15 The
nucleophilic substitution of chlorine atoms with primary or
secondary amines in presence of a hydrochloric acid acceptor
(an organic or inorganic base) can be a controlled with temper-
ature and proceeds as a one-pot procedure. The first substitution
on cyanuric chloride occurs in minutes at 0 °C, while the second
substitution occurs in 12-24 h at ambient temperature, and
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