Chemistry Reference
In-Depth Information
The above modification of butadiene rubber can be carried out to the extent of 3.1 mol.%.
The product is higher in tensile modulus values and is greater in strength than the parent
compound [
75
].
A final example is a 1,3 dipolar addition to pendant azide groups [
87
]. The reaction takes place
with phenyl vinyl sulfoxide in dimethylformamide. Forty-eight hours at 110
C are required for the
azide groups to become undetectable by infra-red spectroscopy. The product precipitates out with
addition of ether [
87
]:
O
O
+
S
+
S
H
N
N
3
N
N
9.2.5.4 The Ene Reaction
The polymers of conjugated dienes can also be modified via the ene reactions [
76
], as for instance:
HX
Y
+
X
Y
where, X
¼
Y can be O
¼
N-, -N
¼
N-,
C
¼
S,
C
¼
O, or
C
¼
C
. An example of this is an addition
>
>
>
<
of triazolidones [
76
]:
R
N
O
O
NN
H
N
N
O
O
+
N
R
This results in formation of pendant urazole groups. The exact structure of the products, however,
has not been fully established. The tensile strength of polymers improves considerably, but it is
accompanied by a dramatic loss in molecular weight [
76
]. Nevertheless, ene reagents like C-nitroso
and activated azo compounds are very efficient in adding to rubber. They add in a few minutes at
temperatures between 100 and 140
C. In the case of the azo compound, the addition can be greater
than 90%.
