Chemistry Reference
In-Depth Information
and bisphenol A (2,2
0
-bis(4-hydroxyphenyl)propane). The degree of polymeriza-
tion of prepolymer 1-20 may be varied to produce liquids (as when x
0) or solids
5
which soften at temperatures up to about 140
C (at x
14).
5
CH
3
C
O
~100°C
(X+1) HO
OH + (X+2) Cl-CH
2
C
H
CH
2
+
(X+2) NaOH
CH
3
CH
3
H
C
OH
CH
3
C
H
H
CH
2
CH
2
O
CH
2
O
C
C
OCH
2
CH
2
O
OCH
2
C
x
CH
3
CH
3
O
+ (X+2)H
2
O + (X+2)NaCl
1-20
(1-8)
The prepolymer can be reacted further with a wide variety of reagents, and its
latent functionality depends on the particular reaction. The conversion of an
epoxy polymer to an interconnected network structure is formally similar to the
vulcanization of rubber, but the process is termed curing in the epoxy system.
When the epoxy “hardener” is a primary or secondary amine like m-phenylene
diamine the main reaction is
O
OH
C
CH
2
NH
2
HN
CH
2
C
H
O
O
O
H
H
+
2 CH
2
C
C
CH
2
NH
2
N
CH
2
C
C
CH
2
H
H
H
OH
H
(1-9)
The unreacted terminal epoxide groups can react with other diamine molecules
to form a rigid network polymer. In this reaction the functionality of the bisphe-
nol A
epichlorohydrin prepolymer 1-20 will be 2 since hydroxyl groups are not
involved and the functionality of each epoxide group is one.
When the hardening reaction involves cationic polymerization induced by a
Lewis acid, however, the functionality of each epoxy group is 2 and that of struc-
ture 1-20 is 4. The general hardening reaction is illustrated in
Eq. (1-10)
for initia-
tion by BF
3
, which is normally used in this context as a complex with ethylamine,
for easier handling.
These examples barely touch the wide variety of epoxy polymer structures
and curing reactions. They illustrate the point that the latent functionality of the
