Chemistry Reference
In-Depth Information
Polyether-Based Supports
Tentagel, described above, is in wide use today in solid phase syntheses. Polyethylene glycol has also
been attached to various other polymers to form support resins. For instance, Fr
ยด
chet and coworkers [
37
]
used cross-linked methacrylate esters of ethylene glycol oligomers in a suspension polymerization to
synthesize hydroxyl group functionalized beads. These beads swell well in a variety of polar solvents.
Another example is that of Grubbs attaching a ruthenium metathesis catalyst to polyethylene [
38
]:
O
O
n
N
N
Mes
Mes
Cl
Ru
Cl
O
10.1.2 Special Gels for Drug Release
Metyjaszewski et al. reported [
39
] preparation of nanostructured hybrid hydrogels for tissue engi-
neering and drug delivery applications. They incorporate poly(oligo (ethylene oxide) monomethyl
ether methacrylate) nanogels of size 100-200 nm into a larger 3D matrix, such as hyaluronic acid gel.
The macroscopic hydrogel acts as a 3D matrix regulator for the drug release. In this work,
polymerizable poly(oligo (ethylene oxide) monomethyl ether methacrylate) nanogels were cova-
lently incorporated into a 3D network via a photo-polymerization process. The introduction of
disulfide moieties into the polymerizable groups resulted in releasable nanogels from cross-linked
3D network under reducing environment.
Tan, Fu, and coworkers [
40
] reported preparation of a pH-sensitive biodegradable polyurethane
for drug release:
O
H
H
O
O
N
O
N
OH
H
O
N
O
2
y
x
polyol
A series of pH-sensitive polyurethanes were synthesized using pH-sensitive macrodiol, shown above,
and a tripeptide chain extender. The obtained polyurethane had a number average molecular weights of
4,500-6,200. The material cleaves in acid media (pH 4-6) and degrades in enzymatic solution.
McCormick and coworkers [
41
] reported the synthesis of a temperature-responsive triblock
copolymer, consisting of
a
b
N
-methoxypropyl
(ethylene oxide)-
-poly(
-(3-aminopropyl)metha-
b
N
cryIamide)-
-poly(
-isopropylacrylamide). At room temperature, the polymer is hydrophilic and
