Chemistry Reference
In-Depth Information
3. The polymeric reagent can also be used as
transfer agents
. Low molecular weight reactants
transfer the functional moiety with the aid of the polymeric agent. This leaves the products in pure
form after filtration and solvent removal.
4. The polymers are used as
carriers
or
as blocking groups
in syntheses [
1
]:
B
C
+
A
A
A
B
+
A
B
C
A
C
B
10.1.1 Support Materials
Many different support materials were developed [
3
,
4
] since the original use by Merrifield of a
polystyrene-based support material for polypeptide synthesis [
5
]. The work of Merrifield is described
in Chap.
8
(see section on proteins). Beads of copolymers of styrene with divinyl benzene are
available commercially and have been widely used as supports for many reactions. Many other
polymeric materials are also used. These can be various other type of copolymers of styrene or with
other polymers. The list includes cellulose, starch, polyalkanes, polyamides, poly(glycidyl methac-
rylate), polyisobutylene, polynorbornene, polyacrylamide, and others. In some instances, even glass
was used. The more prominent support materials are presented below.
10.1.1.1 Materials Based on Polystyrene
Cross-linked polystyrene (copolymer with divinyl benzene) was the original support material used by
Merrifield for polypeptide syntheses. The material is actually a terpolymer of styrene, chloromethyl
styrene, and divinyl benzene.
x
y
z
Cl
x
Copolymers of styrene and divinyl benzene supports have since received many uses and have
undergone many chemical modifications for various reactions as reagents and catalysts. The material
can be functionalized in many ways. Thus, it can be nitrated, chloromethylated, sulfonated, lithiated,
carboxylated, and acylated. The greatest use has been made of the chloromethylated and lithiated
derivatives. These two derivatives can react with nucleophilic and electrophilic reagents,
