Chemistry Reference
In-Depth Information
Alternating copolymerization of styrene with maleic anhydride is also explained by donor
acceptor interactions [
171
]. A charge-transfer complex is seen as the new monomer, a diradical,
which polymerizes through coupling [
171
-
174
].
O
O
+
O
O
O
+
O
donor
acceptor
charge transfer complex
O
O
O
O
O
n
O
diradical
Charge-transfer complexes are also claimed to be the intermediates in free-radical alternating
copolymerization of dioxene or vinyl ethers with maleic anhydride [
176
-
179
]:
O
O
O
O
O
O
+
O
+
O
O
O
donor
O
O
R
O
O
O
O
O
O
O
O
n
where, R is a polymerization-initiating radical. Here, a third monomer can be included to
interpolymerize with the complex that acts as a unit. The product is a terpolymer [
176
,
177
].
A diradical intermediate was also postulated in sulfur dioxide copolymerizations and terpolymer-
izations with bicycloheptene and other third monomers [
173
]. These third monomers enter the
copolymer chain as block segments, while the donor-acceptor pairs enter the chains in a one-to-
one molar ratio. This one-to-one molar ratio of the pairs is maintained, regardless of the overall nature
of the monomer mixtures.
The propagation and termination steps in the above reactions are claimed [
175
,
181
-
183
]tobe
related. As stated, an interaction and coupling between two diradicals is a propagation step. When such
interactions result in disproportionations, however, they are termination steps. This means the charge-
transfer mechanisms are different from conventional free-radical polymerizations. They involve
interactions not only between growing polymer-radicals and monomers but also between polymer-
radicals and complexes. In addition, the polymer radicals react with each other [
175
,
181
-
184
].
