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

206 J. Roovers, B. Comanita
4.2
Dendrimers on Polymers
4.2.1
Dendrimers on Flexible Polymers
In general, the polymerization of macromonomers leads to low MW materials
and the DP of the backbone is often similar to the DP of the macromonomer.
Consequently, these polymers are nearly spherical and resemble star polymers
in dilute solution. However, it has been shown recently that high MW poly(macromonomers)
have a rodlike conformation in dilute solution [102, 103]. In the
particular case studied, polystyrene macromonomers linked by an ethylene oxide
spacer to an end-standing methacrylate group have been polymerized to
DP»1000. It is concluded that the central methacrylic backbone adopts a
stretched conformation due to the constraining long and bulky polystyrene side
chains. The polymer resembles a “bottle brush” [104]. X-ray scattering experiments
in semi-dilute solution further revealed a lyotropic phase consistent with
the high aspect ratio of the polymer [105].
The second impetus to consider monomers with dendritic side groups comes
from the work of Percec et al. on monomers with tapered side chains, e.g., polymerization
of 3,4,5-tris (4'-dodecyloxybenzyloxy) benzoic acid ethylene glycol
(n=1,2,3,4) methacrylates
yields polymers which self-assemble into a tubular supramolecular architecture
with radii between 27 and 36 Å [106]. Dendrimers on polymers may therefore be
expected to influence the backbone conformation and be a possible source of
new polymeric materials. The first macromonomers carrying dendrimers have
been prepared by Fréchet and Hawker who attached their poly(benzyl ether)
dendrimer [G-3], [G-4], and [G-5] (see Scheme 3) to a styrenic functional group
[107] thereby placing seven bonds between the backbone carbon and the focal
point. Copolymerization with styrene produced high MW material. The copolymer
composition is equal to the monomer composition, implying that the dendritic
substituent does not affect the reactivity of the styrenic double bond. Styrenic
monomers with poly(benzyl ether) dendrimer of general structure
(1)
(2)