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predetermined by choice of monomer. The chapter concludes with a discovery trip
into the world of single molecule chemistry. The symbiosis of the thick dendronized
polymers and the atomic force microscope with its resolution in the nanometer range
allows to covalently connecting individual macromolecules at predetermined posi-
tions. These four cases together with the beautiful work of other laboratories [4] show
the richness and diversity of both basic research and application aspects of macro-
molecules with regularly branched lateral substituents. The nomenclature used in this
chapter is to be understood as follows:Mand P stand for macromonomer and polymer,
respectively, and G for generation of the appending dendrons. Please note that for
simplicity a polymer of the same name, for example,
PG2
, may refer to different
chemical structures in different sections of this chapter.
4.2 SYSTEMATIC THICKENING OF POLYMER CHAINS: THE
ATTACH-TO ROUTE TO DENDRONIZED POLYMERS
The large majority of dendronized polymers are synthesized according to the
macromonomer route. This route uses monomers that already carry the dendron of
the final size desired as the lateral substituent of the polymer's main chain repeat units.
It is attractive because of synthetic ease and the high level of perfection achievable for
the dendritic branchwork in the polymer. Ease of synthesis is of course a relative
assessment. Obviously, the effort to synthesize a highly branched macromonomer is
substantially higher than that for simple monomers like methylmethacrylate, which
are often even commercially available. Compared to the attach-to approach to
dendronized polymers (see below), however, in which the generations are built up
by applying synthetic steps repeatedly to polymers, themacromonomer route is in fact
much simpler. All operations are restricted to the relatively low molar mass—
monomeric—regime. This facilitates purification and analytics. The corresponding
dendronized polymer is then obtained in just a single step by polymerizing the
macromonomer. Ideally the dendrons stay untouched during this polymerization.
1
Thus, the macromonomer route directly translates the level of structural perfection
contained in the macromonomers into the product, a substantial benefit, which in the
attach-to alternative has to be heavily fought for. These two reasons made the
macromonomer route what it is today, the prime tool for the synthesis of dendronized
polymers specifically if low-generation representatives are concerned. As far as
higher generations are concerned (beyond approximately G3) a feature becomes
visible that can be disadvantageous and should therefore not be hidden: The main
chain length decreases with increasing monomer generation, sometimes even dras-
tically (Figure 4.1). This certainly applies within the same series of polymers. A recent
example concerning the monomers
[5] (Figure 4.2) illustrates,
however, that the term “generation” should be used with care when representatives of
structurally different series are compared. What actually has an impact on chain
M1(G4)
and
M2(G3)
1
The dendrons should be designed such that chain transfer to monomer and polymer is negligible.
