Chemistry Reference
In-Depth Information
mixtures the excess reactant does not enter the polymerization in the absence of
side reactions and should not be counted in calculating f
av
. Consider a polymeri-
zation that forms AB links and in which n
A
,
n
B
, where n
i
is the number of
equivalents of functional groups of type i. In this case the number of B equiva-
lents which can react cannot exceed n
A
, and therefore
X
N
i
5
2n
A
N
A
1
f
av
5
2n
A
=
(7-16)
N
B
The initial number of monomers is
P
N
i
5
N
0
, and N
0
f
av
is the total number
of useful equivalents of functional groups of all kinds that are present at the start
of the reaction. We define p as the extent of reaction equal to the fraction of func-
tional groups in deficient concentration which have reacted. Obviously 0
1,
and p in stoichiometric mixtures is the fraction of functional groups of either kind
#
p
#
A
A+ B
B
A
AB
B
A
AB
BA
(a)
A B A B B
A B B
(b)
A
A+ B
B
A
AB
B
A
A
A B AA
A B AA
A
A
A
A
B
B
B
A
A
B
A
A
A
(c)
A
+ B B
B A BB
A
B
B
A
BA
A
+
B
B
A
FIGURE 7.3
Some step-growth polymerizations of
1 and any
number of different monomers may be present). (a), (b), and (c) represent different
possible combinations of monomers.
n
-functional monomers (where
n
$
