Chemistry Reference
In-Depth Information
CH
3
C
O
CH
2
=
C
(a)
OCH
3
CH
2
=
CH-CN
(b)
ClCH
2
N
CH
2
CH
2
=C
CH
2
=CH-OCOCH
3
C
OCH
2
CH
CH
2
O
O
CH
2
OCO-C(CH
3
)
=
CH
2
CH
3
H
3
C
CH
2
=
C
C
=
CH
2
CH
3
C
OCO-C(CH
3
)=CH
2
C
O
OCH
2
CH
2
O
C
CH
2
OCO-C(CH
3
)=CH
2
O
(c)
a
a
a
b
b
c
a
a
b
b
Fig.
8
.5
Topological scheme in cross-
linking.
compact material, the polymerisation is performed
in the presence of inert molecules in solution,
so that the polymer network is formed around
aggregates of these so-called 'porogen' molecules,
affording a discontinuous material with open
pores of diameter up to 600 Å.
minimum amount of porogens such as soluble
(linear) polystyrene or dibutyl phthalate is intro-
duced in the medium during the polymerisation
[29].
For practical reasons, due to the techniques of
polymerisation, the final materials appear as trans-
luscent or opaque spherical beads of size 0.2-2 mm
in diameter, which allows easy handling, transfer
and filtration.
The most popular starting material is 'Merrifield's
polymer'—a gel-type chloromethylated polystyrene
(P—C
6
H
4
-CH
2
-Cl) with which Merrifield performed
the first successful synthesis of polypeptides [1].
More than 50 different functional groups have
been introduced through nucleophilic reactions at
the benzylic position [30], a few examples are given
A schematic view would correspond to a sponge-like
material with large channels where the post-func-
tionalisation gives active groups that are at the
surface of the stiff walls (Fig. 8.6b).
2.4 Polystyrenes
Some macroporous styrene-based copolymers may
exhibit interesting properties when a high porous
volume is obtained; this can be obtained when a
