Chemistry Reference
In-Depth Information
8
0 °C
7
5 °C
6
8 °C
6
6 °C
6
5 °C
6
4 °C
6
3 °C
6
2 °C
6
1°C
6
0 °C
5
8 °C
5
6 °C
5
4 °C
5
0 °C
8
7
6
5
4
3
2
1
0 ppm
FIGURE 4.6
Fully reversible temperature-dependent proton NMR spectra of
PG2(MT)
(2.0 wt% in D
2
O) in the range from 50 to 80
C.
reflect the expectations based on hydrophilicity/hydrophobicity considerations and
show that even without any additions (e.g., of salts) a broad and highly relevant
temperature window can be covered with slightly modified polymers. Interestingly, it
can also be concluded that there does not seem to be a significant generation
dependence. This is perhaps the most important finding as it may point toward
mechanisms in which the collapse of the outermost units determines the LCST to a
large degree and the internal dendritic units play less of a role [25]. This proposal is
100
heating
cooling
PG1(ET)
80
PG1(MD)
PG2(ET)
PG2(MD)
60
PG3(ET)
PG1(MT)
40
PG2(MT)
20
0
20
30
40
50
60
70
80
Temperature (ºC)
FIGURE 4.7
Transmittance versus temperature for the various OEG-based dendronized
polymers synthesized, indicating unprecedentedly sharp and fully reversible transitions.
