Chemistry Reference
In-Depth Information
monomers is high then the formation of “genetic” zwitterions is favored. As the concentration of
macro-zwitterions becomes high and the monomer concentration decreases, the macro zwitterions
react preferentially with each other. When stoichiometry is not observed and
-propiolactone
molecules predominate in the reactions mixture, the carboxylate end groups can react in various
ways. They can react not only with the cyclic onium sites of the zwitterions, but also with free
b
b
-propiolactones and incorporate more than 50% of the propiolactone units [
214
].
Another example of such copolymerization is that of 2-oxazoline with acrylic acid. The reaction
can be carried out by combining the two in equimolar quantities and then heating the reaction mixture
to 60
C in the presence of a free radical inhibitor. Such an inhibitor can be
p
-methoxy phenol. The
reaction mixture becomes viscous as an alternating copolymer forms [
218
]:
O
N
COOH
+
O
N
n
O
H
O
-propiolactone.
The acrylic acid is converted into the same repeat unit as the one that forms from ring-opening of
b
This copolymer is identical to the one obtained from reacting 2-oxazolone with
b
-propiolactone shown in the previous example. The suggested reaction mechanism involves a
nucleophilic attack by oxazolone on acrylic acid and is followed by proton migration [
214
]:
A similar proton migration takes place in copolymerizations of acrylamide with cyclic imino
ethers. The proton migration is part of the propagation process [
219
]. Other examples are copolymer-
izations of a nucleophilic monomer, 2-phenyl-1,2,3-dioxaphospholane with electrophilic monomers
[
224
,
225
]. Here too the electrophilic monomers can be either acrylic acid or propiolactone. Identical
products are obtained from both reactions [
223
]:
O
COOH
O
P
COOH
P
+
O
O
O
O
COO
O
P
P
+
O
O
O
