Chemistry Reference
In-Depth Information
of polar cross-linking materials, like oligomers of glycols. One example is a cross-linked polystyrene-
poly(ethylene glycol) composite, known as
Tentagel
[
10
]. It can be illustrated as follows:
z
x
y
z
x
y
O
+
HO
n
O
x
Cl
OH
x
n
Another example is work by Bradley and coworkers who incorporated short oligomer (polyethyl-
ene glycol) groups into the backbone of the cross-linked polystyrene [
11
]. The oligomer poly
(ethylene glycol) in this preparation also acts as a spacer to separate the polystyrene backbone
from locations of the reactions. The material was used efficiently in a solid phase peptide synthesis.
Toy et al. [
12
] demonstrated that by replacing divinyl benzene with more flexible compounds
usually increases their mechanical stability and allows them to absorb more solvent. In addition, when
the cross-linked compounds contain oligomers of such materials as ethylene glycol, the compatibility
with polar solvents increases. Subsequently, Janda and coworkers used polytetrahydrofuran in sus-
pension polymerization of styrene to prepare general solid support resins for organic syntheses [
13
].
x
y
z
+
susspension
polymerization
R
O
O
O
R
n
O
n = 1,3.5,9.5
z
The material became known as
Janda Gel
[
13
]. The preparation of this gel with
n
equal to one is
illustrated above [
14
].
An interesting application of cross-linked styrene resins that are similar to the Janda gel was developed
byKobayashi and coworkers, who used suchmaterials to encapsulatemetal catalysts [
15
]. The technique
