Chemistry Reference
In-Depth Information
Figure 13.16 Stackplot of electron paramagnetic resonance (EPR) spectra of 2,2,6,6-
tetramethylpiperidine N-oxide (TEMPO)-functionalized dendrimers with 5, 10, 25, 50, 75,
90, and 95% TEMPO.
line-broadening effects is exhibited by the ratio of peaks in the EPR spectra. The
ratio of peak A to peak B in Figure 13.16 is plotted in Figure 13.17 for all of the
TEMPO-functionalized dendrimers. In all cases, the A/B ratio of peak heights is
independent of the nature of the second isothiocyanate. Thus, for functionalization
of dendrimers using a sequential addition strategy, the end-group patterning is not
significantly influenced by the nature of the end group.
What, then, is the end-group pattern that emerges from sequential addition of reac-
tive components? We calculated the expected line-broadening effects for randomly
functionalized dendrimers and compared them to the experimentally observed line-
broadening effects. Figure 13.18 compares the experimental results from the stackplot
in Figure 13.16 to the calculated results. Because a wide body of literature now indi-
cates that dendrimer end groups can backfold into the interior of the dendrimer
(Ballauff and Likos 2004), we included a volume shell
in our calculations.
Figure 13.17 Graph of line-broadening effects for 2,2,6,6-tetramethylpiperidine N-oxide
(TEMPO) and R-4-isothiocyanato (R-NCS) functionalized dendrimers from Figure 13.15.
NCS-TEMPO was added first half of the time and R-NCS was added first half of the time.
