Chemistry Reference
In-Depth Information
A second mechanism, proposed by Imoto and Choe [
20
] shows the complex as an intermediate step:
O
O
N
O
+
O
O
O
N
N
O
O
O
O
+
O
O
N
+
O
O
The dimethyl aniline radical-cation, shown above, undergoes other reactions than addition to the
monomer. The benzoyl radical is the one that initiates the polymerizations.
Presence of electron-releasing substituents on diethyl aniline increases the rate of the reaction with
benzoyl peroxide [
21
]. This suggests that the lone pair of electrons on nitrogen attack the positively
charged oxygen of the peroxide link [
22
].
By comparison to peroxides, the azo compounds are generally not susceptible to chemically
induced decompositions. It was shown [
23
], however, that it is possible to accelerate the decomposi-
tion of
a
0
-azobisisobutyronitrile by reacting it with bis(-)-ephedrine-copper (II) chelate. The
mechanism was postulated to involve reductive decyanation of azobisisobutyronitrile through coor-
dination to the chelate [
23
]. Initiations of polymerizations of vinyl chloride and styrene with
a
,
a
0
-
azobisisobutyronitrile coupled to aluminum alkyls were investigated [
24
]. Gas evolution
measurements indicated some accelerated decomposition. Also, additions of large amounts of tin
tetrachloride to either
a
,
a
0
-azobisisobutyronitrile or to dimethyl-
a
0
-azobisisobutyrate increase the
a
,
a
,
decomposition rates [
25
]. Molar ratios of [SnCl
4
]/[AIBN]
19.53
increase the rates by factors of 4.5 and 17, respectively. Decomposition rates are also enhanced by
donor solvents, such as ethyl acetate or propionitrile in the presence of tin tetrachloride [
25
].
¼
21.65 and [SnCl
4
]/[MAIB]
¼
