Chemistry Reference
In-Depth Information
So after 350 days at 100°C, pH 2:
[]
η
(
350
days
)
38
.
3
≤
=
0
89
[]
η
(
0
day
)
42
.
According to the Mark-Houwink law: [η] = KM
α
where K and
are constants
depending on the polymer, solvent and temperature of viscosimetric measure-
ments; and M is the number average molecular weight. Thus
α
[]
[]
1
/
α
M
(
350
days
)
η
(
350
days
)
=
M
(
0
day
)
η
(
0
day
)
M
(
350
days
)
As
α
~ 0.7 one obtains:
≤
0
85
. The number of chain scissions,
M
(
0
day
)
n, after 350 days immersion time at 100°C, pH 2 is given by:
1
1
1
1
= 9.5.10
-3
mol.kg
-1
.
n
=
−
≤
−
1
M
M
M
0
.
85
o
o
3.2.10
-10
mol.kg
-1
.s
-1
. As ex-
So the average rate of chain scissions v
c
is: v
c
≤
pected, v
c
is lower than v
H
.
The conclusion is that all the experimental data are consistent and indicate that
hydrolysis is extremely low at 100°C, pH 2. One possible explanation is that the
amide and acid resulting from the first hydrolysis reaction remain “trapped” in a
cage favoring their immediate recombination (as shown in the following scheme).
The kinetic study of polyamide 11 hydrolysis [9] showed that the recombina-
tion was favored at temperatures between 100 and 140°C.
Between 170-180°C, the two main experimental facts are:
(i) Crosslinking: gelation occurs after 21 days at 170°C and after 6 days at
180°C.
(ii) A significant mass gain for PEI (close to 20%) in wet state.
Crosslinking could result from intermolecular condensation between an amine
and an acid as shown in the following scheme:
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