Polyimide and high-temperature adhesive of polyimide

A method for adhering a first substrate and a second substrate, which comprises:

• applying a solution of a polyimide dissolved in an organic solvent, onto a surface of the first substrate and optionally onto a surface of the second substrate, the polyimide consisting essentially of recurring units of the formula:
• ##STR17## wherein Y is radical --S-- or --C(CH.sub.3).sub.2 --, Z is:
• ##STR18## and R is a tetra-valent radical selected from the group consisting of (a) an aliphatic radical having at least 2 carbon atoms, (b) a cyclo-aliphatic radical, (c) a monoaromatic radical, (d) a condensed polyaromatic radical wherein the aromatic radicals are mutually connected with a bond or a crosslinking function, and (e) a non-condensed polyaromatic radical wherein the aromatic radicals are mutually connected with a bond or crosslinking function, and the organic solvent is selected from the group consisting of a halogenated aliphatic hydrocarbon, phenol, a halophenol, cresol, nitrobenzene, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, sulfolane and N,N-dimethylformamide;
• overlapping the applied surface of the first substrate with an untreated or applied surface of the second substrate;
• preheating the overlapped substrates to remove the organic solvent present;
• and heating the overlapped substrates at a temperature of from 50.degree. to 400.degree. C. under a pressure of from 1 to 1,000 kg/cm.sup.2.