Chemistry Reference
In-Depth Information
that decomposes to formaldehyde upon heating. It can also come from hexamethylenetetramine, a
condensation product of formaldehyde with ammonia:
N
+
O
4NH
3
6
N
N
N
Hexamethylenetetramine decomposes to formaldehyde and ammonia upon heating. Some of the
ammonia is picked up by the novolacs with the result that there are some benzylamine bridges in the
product:
OH
H
N
OH
The mechanism of this reaction is discussed in the next section.
7.12.3 Ammonia-Catalyzed Phenolic Resins
These resins differ from the other resols, because there are some benzylamine bridges present in their
structure. The reactions result in early losses of water and allow higher molecular weight buildups
before the resins gel. Nitrogen-containing resols are darker in color than regular resols. The di
benzylamine bridges form as follows [
145
]:
OH
OH
OH
OH
N
2
+
NH
3
(RNH
2
)
H
The overall mechanism can be shown as a special case of a Mannich reaction:
H
H
(R)
H
+
NOH
(R)
H
N
(R)
H
N
O
O
H
H
H
O
O
(R)
H
(R)
H
+
N
NOH
+
H
2
O
H
H
