The paper is devoted to the modification of the polyimide based on pyromell
itic dianhydride and 4,4'-diaminodiphenyloxide with phosphoric and boric an
hydrides. It is demonstrated that, due to the use of phosphorus- and boron-
containing polyamidoacid compositions for casting the polyimide films, one
can significantly increase their heat resistance without substantial expend
itures while, at the same time, preserving the film-forming ability and mec
hanical properties of the polyimide.