Chemistry Reference
In-Depth Information
7.11.1 Preparation of Commercial Epoxy Resins
The earliest developed commercial epoxy resins were diglycidyl ethers of 4,4
0
-isopropylidine-
diphenol (Bisphenol A) formed by reacting epichlorohydrin with the diphenol. The reaction
sequences involve formations of alkoxide ions, followed by nucleophilic additions to the least
hindered carbons [
134
]:
HO
OH
+
OH
HO
+
O
H
2
O
O
+
H
O
Cl
O
H
O
O
This is followed by ring closures through internal displacement of chloride ions:
HO
HO
O
O
Cl
+
O
Cl
O
As explained in the discussion on phenoxy resins, a reaction of two moles of epichlorohydrin with
one mole of the diphenol yields higher molecular weight by-products and only 10% of the diether:
O
O
O
O
O
O
x
OH
where
1-10
To obtain high yields of the diether, the quantities of epichlorohydrin in the reaction mixtures must
be doubled or tripled [
131
]. This can result in yields as high as 70%. Another advantage of a large
excess of epichlorohydrin in the reaction mixtures is that it serves as a solvent [
134
].
A different route to the diglycidyl ethers is via Friedel-Craft reactions [
135
]:
x ΒΌ
O
+
0.1 - 0.2 % ZnCl2
Cl
HO
OH
Cl
O
O
Cl
OH
OH
