Preparation of phenol formaldehyde resins containing pendant isoimides and their isomerization to stable resins

Abstract

Aminophenols were allowed to react with maleic and phthalic anhydrides, producing high yields of the corresponding N-(hydroxyphenyl) maleamic and phthalamic acids, respectively. The amic acids were dehydrated to the corresponding maleisoimides and phthalisoimides with N,N-dicyclohexylcarbodiimide or ethyl chloroformate as the dehydrating agent. Formaldehyde was allowed to react with the products in the presence of an acid catalyst, and novel phenol formaldehyde resins (Novolac-like) were produced. The resins on treatment with a sodium carbonate solution or on prolonged heating at 50 °C suffered rearrangement to corresponding phenol formaldehyde resins with pendant imides. This rearrangement was accompanied by an increase in the softening point and thermal stability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3244–3252, 2000