PREPARATION AND PROPERTIES OF POLYISOIMIDE AS A POLYIMIDE-PRECURSOR

The reactions of N-phenylphthalamic acid with various dehydrating agents have been investigated. N,N'-dicyclohexylcarbodiimide (DCC) and trifluoroacetic anhydride with triethylamine (TEA) were found to be suitable dehydrating agents for the formation of N-phenylphthalisoimide. The isomerization of isoimide to imide was catalyzed by acids or bases, where 1,8-diazabicyclo[5,4,0]-7-undecene (DBU) was most effective and a quantitative yield of imide was obtained quickly. Various polyisoimides were prepared by the cyclization of polyamic acids using DCC. These polyisoimides were relatively stable above their glass transition temperature (T(g)), but easy to convert to corresponding polyimides by high thermal treatment (>250-degrees-C). Furthermore, there was a change of 20-70-degrees-C in T(g) due to isomeric conversion.