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

198 J. Roovers, B. Comanita
Fig. 5. Dependence of the hydrodynamic radius of poly(benzyl ether) dendrimers on molecular
weight;m monodendron; o tridendron; data on low MW polystyrene (D) in a good
solvent are included for comparison
ed especially for the low MW dendrimers. The same study [76] reported results
in three different solvents of decreasing polarity, water at pH 8.0 with
0.1 mol/l NaCl, methanol and n-butanol. At low MW up to the fourth generation,
R h~M 0.4 and the dimensions of the dendrimers vary little with the solvent
quality. This behavior is comparable to that of low MW organic compounds and
oligomers. For example, Yamakawa et al. showed that poor and good solvent distinctions
disappear for polystyrene oligomers with MWR h (MeOH)>R h (n-BuOH). Such behavior is typical of
polymers and reflects the influence of solvent on long-range interactions. It is remarkable
that hydrodynamic radii of PAMAM dendrimers in MeOH based on
the ammonia core are in good agreement with the hydrodynamic radii of the
dendrimers based on ethylenediamine core [3, 77]. These results have also been
included in Fig. 4.
Intrinsic viscosity results on DAB(CN) x and DAB(NH 2 ) x have been quoted in
various publications [5, 71, 78]. Unfortunately, the solvent and experimental
conditions are not specified. R h is found to increase by a constant increment for
five generations. In a double logarithmic plot of R h against MW it is found that
the slope decreased from slightly larger than 0.4 at low MW to about 0.3 at high
MW. Intrinsic viscosities of four generations of carbosilane dendrimers [79] (see
Fig. 3a for structure) and four generations of poly(dimethylsiloxane) dendrimers
[80] lead to R h–M n dependencies with n=0.4 for these low MW dendrimers.