Chemistry Reference
In-Depth Information
Step-growth polymerizations at high temperatures produce nearly random copoly-
mers because of end-group interchange reactions like Eq. (7-14) between macromole-
cules. Interfacial and low-temperature solution polycondensations are conducted under
essentially irreversible conditions, by contrast. In these cases the average copolymer
composition and blocklike character of the product may depend on the reaction condi-
tions and relative reactivity of the functional groups involved in the polymerization.
PROBLEMS
7-1
Polybenzimidazoles
are made
by
a
two-stage
step-growth melt
polymerization:
H
2
N
NH
2
-H
2
O
n
n
+
φ
-
OH
H
2
N
NH
2
C
C
O
O
O
O
φ
φ
N
N
φ
N
N
n
H
H
What extent of reaction is needed to produce n
200 in the above for-
5
mula? Carry four decimal places in your answer.
7-2
Polyamide A has the structure
HN
CH
2
NH
C
O
CH
2
C,
O
6
4
M
n
5
60
;
000 and M
w
5
120
;
000
:
Polyamide B has the structure
HN
CH
2
NH
C
O
CH
2
C,
O
8
6
The two polyamides are mixed in equal
quantities by weight and are held at 280
C for 7 h. Interchange reactions
can come to equilibrium in this time but no further polymerization could
take place bec
aus
e con
de
nsation products were not removed from the sys-
tem. What are M
n
and M
w
of the final, equilibrated system?
M
n
5
90
;
000 and M
w
5
180
;
000
:
7-3 Can the following alkyd recipe be carried to “complete” conversion
without gelling?
