Chemistry Reference
In-Depth Information
trichloride-amine complexes, and imidazole derivatives. All these compounds initiate polymerizations
of the epirane ring.
Cross-linking of the epoxy resins with primary and secondary amines is somewhat different
because they react by nucleophilic addition to the epirane ring:
O
R
+
N
R
NH
2
HOH
O
R
N
OH
HO
A considerable amount of evidence suggests that this reaction is accelerated by proton donors.
Such donors may be water, phenols, or alcohols [
136
]:
HO
H
H
O
O
+
+
R
NH
2
H
2
O
R
N
H
HOH
OH
R
OH
+
R
N
N
H
2
O
H
H
Epoxy resins can also be cured with the aid of ionic liquids [
136
]. The cross-linking reaction takes
place at elevated temperatures
Highly idealized pictures of reaction products from Bisphenol A diglycidyl ethers with diamines
can be found in the literature [
137
]. In actuality, the products are probably more complex. They are
certainly complex when reactions involve higher molecular weight epoxy resins.
Many different aliphatic and aromatic polyamines are available for cross-linking epoxy resins.
Some of these are ethylenediamine, diethylene triamine,
triethylene tetramine,
tetraethylene
pentamine, and many others. Among the aromatic polyamine are
p
-phenylene diamine,
m
-phenylene
diamine, 4,4
0
-diaminodiphenyl-methane, and diaminodiphenylsulfone.
A special cross-linking agent for epoxy resins is dicyanodiamide, also referred to by its trade name
as cyanoguanidine. It is used for high temperature cures and it is believed that the compound
condenses with the epirane structures to form 2-aminooxazoline derivatives [
137
]:
H
H
2
NN N
O
+
O
N
H
dicyanodiamide
N
O
N
O
H
