Chemistry Reference
In-Depth Information
O
O
Na
2
Si0
3
5H
2
O
O
O
The higher molecular weight resins that form in the presence of caustic result from reactions of
glycidyl ethers with phenoxy anions:
OH
O
O
O
+
O
The number of repeat units in the above resin is determined by the molar ratios of the reactants.
This is illustrated in Table
6.9
.
7.11.2 The Cross-linking Reactions
Diglycidyl ethers of Bisphenol A cannot be cross-linked through heating alone. Chemical cross-linking
agents must be added. Most commonly used compounds are tertiary amines, polyfunctional amines, and
acid anhydrides. Lewis acid, phenols, and compounds like dicyandiamide, however, are also used.
The reactions between tertiary amines and epoxy groups result in formations of quaternary bases:
O
+
R
2
N
R
3
N
O
The product reacts with hydroxyl compounds to form anions:
O
OH
+
R
3
N
R
3
N
HO
R'
+
O
R'
The anions in turn initiate polymerizations of the epoxy groups:
O
R
+
R
O
O
O
O
O
R
R
O
O
O
O
O
R
O
O
O
O
etc.
Because the monomer is a diepoxide, a three-dimensional lattice results. A similar three-dimensional
product forms from reactions with other cross-linking materials, like boron trifluoride-etherate, boron
