Chemistry Reference
In-Depth Information
LaI
2
n
1,4-polyisoprene
4.4.2.2 Hydrogen Transfer Polymerization
Anionic polymerization of unsubstituted acrylamide, catalyzed by strong bases, does not yield typical
vinyl polymers. Instead, the product is a 1,3-adduct, poly(
-alanine) [
214
]. Two alternate reaction
paths were originally proposed [
214
]. These can be shown as follows:
b
1.
B
+
BH
+
O
NH
2
O
H
B
B
CH
B
+
2,
O
NH
2
O
2
O
NH
Subsequently, studies of the rate of disappearance of acrylamide in dry sulfolane or pyridine with
potassium-
t
-butoxide initiator led to the following proposed mechanism [
215
]:
B
B
CH
+
+
NH
2
O
O
NH
2
O
NH
2
O
H
Propagation proceeds in this manner [
215
]:
O
O
O
NH
2
+
O
O
NH
NH
2
NCHNH
2
H
O
O
O
O
O
O
+
etc.
NH
2
N
NH
NC
H
N
NH
2
H
H
H
The propagating center is neither an ion nor a radical, but a carbon to carbon double bond at the
end of the chain. The monomer anion adds to this double bond. This process is a step-growth
polymerization and the monomer anion is called an
activated monomer
. Not all acrylamide
polymerizations, initiated by strong bases, however, proceed by a hydrogen transfer process.
Depending upon reaction conditions, such as solvent, monomer concentration, and temperature
some polymerizations can take place through the carbon to carbon double bonds [
216
].
