332 HIGH PERFORMANCE POLYMERS
PAIs must be used because of the lack of solubility in
cresol [91].
PAI types that are soluble in cresol can be produced
by the reaction of trimellitic acid anhydride with cresol
to give the cresyl ester. This ester is reacted with MDI
andthenwith4,4
-diaminodiphenylmethane. PAI is
rendered soluble in cresol by the modification with
ε-caprolactam. A disadvantage is that this type is no
longer purely aromatic and the thermal properties are
adversely affected.
It was found that aromatic imide and amide form-
ing components with a functionality of more than two
yield products that are soluble in cresol [91]. Additives
for wire enamels are phenolic resins, melamine resins,
fluorinated compounds, or, benzyl alcohol. Crosslink-
ing