Chemistry Reference
In-Depth Information
Table 11.1
Initiation of Anionic Polymerization by Living Polymer Ends
Monomer
e value
α
-Methylstyrene
0.81
2
Styrene
0.80
2
Butadiene
0.50
2
Isoprene
0.55
2
Methacrylate esters
0.20
0.40
Ethyl acrylate, butyl acrylate
0.55
0.85
Acrylonitrile
1.23
Ethylene oxide, propylene oxide
—
α
-Cyanoacrylates
—
There are exceptions to this guideline, however. Thus,
α
-methylstyryl initia-
tion of styrene or styryl initiation of isoprene are both faster than the reverse
initiations. If inductive effects only are considered, then positive
e
numbers favor
anionic polymerizability.
11.2.2.3
Metal Amides
Styrene and other monomers can be polymerized by potassium amide in liquid
ammonia. The dielectric constant of the solvent is quite high (
22) and this is
one of the few anionic systems in which the active centers behave kinetically as
free ions:
B
+
-
(11-5a)
KNH
2
K
+
NH
2
H
H
NH
2
-
-
H
2
N
CH
2
+
CH
2
C
C
(11-5b)
Also because of the unusual nature of this solvent, chain transfer is important
in this system:
H
-
C
+
CH
2
CH
3
CH
2
3
(11-6)
-
+
NH
2
