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

Dendrimers and Dendrimer-Polymer Hybrids 215
Fig. 6. Phase diagram of ABA poly(benzyl ether) dendrimer PEO in MeOH:H 2 O (1:1)
at the focal point. The nonpolar dendrimer exerts a large solubilizing effect on
the highly polar rotaxane which allows its study in a wide range of solvents.
Dendrimers that are prepared by the divergent method lack the focal group
to attach them to a polymer chain. Such dendrimers must be grown from a preformed
polymer having an end-standing functional group. The first synthesis by
this method used glycine modified PEO and poly(a,e-lysine) to grow a poly(a,e-
L-lysine) dendrimer [129] (See Fig. 3b for structure). Up to four generations of
lysine have been added. The PEO-dendrimer is purified at each generation by
precipitation in diethylether similar to the Merrifield procedure. At the fourth
generation the MW of the poly(a,e-L-lysine) dendrimer and PEO are comparable.
These amphiphilic block copolymers decrease the surface tension of water
and form micelles in solution.
Poly(propylene imine) dendrimers (see Scheme 1 for structure) have been
constructed step by step onto an amine functionalized polystyrene [38, 130,
131]. The challenge in this synthesis is finding conditions for the poly(propylene
imine) synthesis under which the low MW polystyrene (MW=3200) is soluble
[38]. Similar poly(imine) dendrimers with carboxylic acid end groups have also
been prepared [130]. The poly(propylene imine) dendrimer has also been synthesized
on an amino-terminated poly(2-methyl-2-oxazoline) [132].
Because of the commercial interest in amphiphilic block copolymers the
properties of the amphiphilic linear polymer-dendrimer have been most extensively
studied. An illustration of the various phases that can be observed is
shown in Fig. 6 for the case of an ABA type block copolymer, where A is the hydrophobic
dendrimer and B the hydrophilic PEO [119]. The exact location of the