PURPOSE: To obtain a modified polyimide excellent in heat resistance and adhesion and useful for liquid crystal orientation films, surface protective films for semiconductor elements, α-ray shielding films, etc., by polycondensing a specified tetracarboxylic acid dianhydride with an aromatic diamine.

CONSTITUTION: A tetracarboxylic acid dianhydride (a) of at least 0.1mol% siloxane-containing tetracarboxylic acid dianhydride (a) of formula I (wherein R1W2 are each H or alkyl, R3W6 are each a 1W6C hydrocarbyl and n is 1W10) and at most 99.9mol% other aromatic tetracarboxylic acid dianhydrides (b) (e.g., pyromellitic dianhydride) is slowly added to a polar solvent solution of an aromatic dimaine (B) of formula II or III [wherein B is a (substituted) phenylene, a (substituted) biphenylele or a (substituted) naphthylene and Z is CH2, O, S or SO2] at 50°C or below to obtain a polar solvent solution of a polyamic acid as a procursor of a polyimide. This solution is suitably applied and heated to a temperature of 250W300°C to effect a ring closure reaction to obtain a coating or film of a siloxane-modified polyimide.