Biomedical Engineering Reference
In-Depth Information
diblock, high selectivity means a high likelihood of micelle formation. If the
solvent is selective enough, the less soluble blocks (high-CP) are induced to
precipitate, and form the core of micelles, while the more soluble blocks (low-
CP) form the corona. As shown in Figures 13.10 and 13.11, PEG has a low
CP in trifluoromethane, while PCL has a very high one (above the
experimental range). This means trifluoromethane has high selectivity and
high likelihood of micelle formation with PEG-b-PCL, which is indeed the
case. However, in dimethyl ether, the difference between the two homo-
polymer CPs is small, which means low selectivity and low probability of
micelle formation.
In fact, dimethyl ether did not produce micelles at 1 wt%, but it did at 2 wt%
in a small low-temperature region. More important, dimethyl ether exhibited
much lower CPs, which suggests a high capacity for PEG-b-PCL. This
suggested combining the high selectivity of trifluoromethane with the high
capacity of dimethyl ether simply by mixing the two pure solvents.
Figure 13.12 shows that mixing the two solvents produced a nearly linear
d
n
4
y
3
n
g
|
1
Figure 13.14
Cloud pressures of tamoxifen, PEG-b-PCL (5k-b-5k), and mixture and
micellization pressure of PEG-b-PCL (5k-b-5k) in near-critical
trifluoromethane. The concentrations of polymer and drug in solution
are 1 and 0.1 wt%, respectively. (Reproduced from Tyrrell et al.
20
with
permission from the American Chemical Society.)
