Preparation of N-substituted oligo-imides

A process for the preparation of an oligoimide, comprising reacting a dicarboxylic acid anhydride with a amine, said anhydride being represented by the formula:

• ##STR16## and said amine being represented by the formula:
• R----NH.sub.2).sub.n [III]
• in which formulae n is a positive integer which is less than or equal to 5, R is an organic radical of valency n, having not greater than 50 carbon atoms, and D represents a divalent radical selected from the group consisting of ##STR17## in which m is equal to 0 or 1 and Y represents hydrogen, chlorine or methyl, said reaction being carried out in the presence of a catalyst system comprising a mixture of a compound (1) and a compound (2), (1) being a strong inorganic or organic acid having at least one oxygen atom present thereon and which possesses at least one acid functionality having an ionization constant in water which is not greater than 3, and (2) being an ammonium salt of said acid, the cationic ammonium moiety of said salt being at least di-N-substituted by organic radicals.