Chemistry Reference
In-Depth Information
If donor-acceptor interactions and subsequent polymerizations occur upon irradiation with ultra-
violet light, the reactions can be very selective. An example is a triphenylphosphine interaction with
acrylic monomers [
193
]:
O
hν
O
+
P
3
O
O
P
3
O
O
P
3
This reaction does not occur, however, between triphenylphosphine and styrene or vinyl acetate [
193
].
The nature and the amount of solvent can influence the yield and the composition of the
copolymers in these copolymerizations. Thus, copolymerization of phenanthrene with maleic anhy-
dride in benzene yields a 1:2 adduct. In dioxane, however, a 1:1 adduct is obtained. In dimethyl
formamide, no copolymer forms at all [
193
]. Another example is a terpolymerization of acrylonitrile
with 2-chloroethyl vinyl ether and maleic anhydride or with
-dioxene-maleic anhydride. The amount
of acrylonitrile in the terpolymer increases with an increase in the
p
p
-electron density of the solvent in
the following order [
194
]:
xylene
toluene
benzene
>
chlorobenzene
chloroform.
The ratio of maleic anhydride to the vinyl ether in the product remains, however, equimolar.
Whether the concept of charge-transfer complexes in copolymerizations is fully accepted is not
certain. Much of the accumulated evidence, to date, such as UV and NMR spectroscopy, does support
it in many systems [
195
]. Further support comes from the strong tendencies to form alternating
copolymers over a wide range of feed compositions, and also from high reaction rates at equimolar
feed compositions [
171
]. On the other hand, as shown above, it was claimed in the past that
copolymerization of styrene with maleic anhydride involves charge-transfer complexes [
171
,
181
-
183
]. This, however, is now contradicted in a publication of a study of radical copolymerization
of maleic acid with styrene. The reaction was carried out in a dioxane solution at 70
C. The authors
reported that UV spectroscopy fails to show presence of a charge transfer and formation of a complex
between the two monomers in the copolymerization system [
196
].
3.12 Polymerization of Complexes with Lewis Acids
Some polar vinyl monomers such as methyl methacrylate or acrylonitrile interact and complex with
Lewis acids. They subsequently polymerize at a faster rate and to a higher molecular weight than can
be expected otherwise. The effective Lewis acids are ZnCl
2
, AlCl
3
, Al(C
2
H
5
)
2
Cl, AlCl
2
(C
2
H
5
),
SnCl
4
, and some others [
197
-
199
]. Complexes can form on an equimolar basis and undergo
