Chemistry Reference
In-Depth Information
H
H
N
CH
2
N
C
O
CH
2
C
O
6
4
100
7-4
If only bifunctional monomers are present and there are equivalent concentra-
tions of functional groups of opposite kinds, then f
av
5
2. This is the case, for
example, when a high-molecular-weight
linear polymer is being synthesized.
Under these conditions
Eq. (7-19)
becomes
2
1
X
n
5
(7-20)
2p
5
2
1
2
p
2
0.95)
2
1
20. If hexamethylene
diamine and adipic acid were being reacted, the number average molecule would
have structure 7-4 with 10 repeating units. This is an oligomer but would not yet
be considered to be a polymer. At p
When the reaction is 95% complete, X
n
5
(1
2
5
5
0.98, 98% of the functional groups will
have been reacted, X
n
5
50, and the nylon-6,6 of 7-4 would have
a
molecular
weight that is barely high enough for fiber formation. At p
000
and the polymer melt is becoming too viscous for fiber spinning. Still higher
molecular weights and degrees of conversion are needed, however, when the
same polymer is
D
0.995, M
n
C
20
;
Table 7.1
Simplified Alkyd Recipe
Equivalents
a
Ingredient
Functionality
Moles
(i) Fatty acid
b
1
1.2
1.2
Phthalic anhydride
2
1.5
3.0
Glycerol
3
1.0
3.0
1,2-Propane glycol
2
0.7
1.4
4.4
8.6
(ii) Fatty acid
1
0.8
0.8
Phthalic anhydride
2
1.8
3.6
Glycerol
3
1.2
3.6
1,2-Propane glycol
2
0.4
0.8
4.2
8.8
(CH
3
a
CH
2
a
)
a
4
CH
5
CH
a
CH
2
a
CH
5
CH
a
(
a
CH
2
a
)
a
7
COOH) would air dry to form cross-linked
films.
a
The number of equivalents equals the number of functional groups here.
b
If the fatty acid were an unsaturated species like linoleic acid the alkyd
