An aromatic polyimide containing pendent hydroxyl groups ortho to the heter
ocyclic imide nitrogen was found to rearrange to a polybenzoxazole, with qu
antitative loss of carbon dioxide, upon heating above 490 degrees C in an i
nert atmosphere. A hydroxy-containing polyimide film based on 3,3',4,4'-bip
henyltetracarboxylic dianhydride (BPDA) and 3,3'-dihydroxy-4,4'-diaminobiph
enyl (HAB) was pre pared and converted to a fully aromatic polybenzoxazole
by heating at 500 degrees C for 1 h under nitrogen. The resulting polybenzo
xazole film was found to be amorphous by small angle X-ray scattering (SAXS
). The film also displayed excellent solvent resistance and good thermal st
ability by thermogravimetric analysis with 5% weight loss in nitrogen occur
ring at 625 degrees C. A hydroxy-containing imide model compound was also f
ound to undergo thermal conversion to a bisbenzoxazole when heated above 40
0 degrees C under nitrogen. (C) 1999 Elsevier Science Ltd, All rights reser
ved.