PURPOSE: To obtain a polymer film, useful as an insulating film, moistureproof film, etc., for electronic parts in semiconductor devices, etc., and composed of a specific polymaleimide polymer excellent in strength by evaporating the aforementioned polymaleimide in a vacuum and forming a vacuum deposition film.
CONSTITUTION: The objective polymer film, obtained by heating a polymaleimide, having at least 3 benzene rings and ≥2 maleimide structures expressed by formula I [a compound expressed by formula II (X is O, SO 2 , etc.; benzene ring may be substituted with halogen, alkyl, etc.; k is ≥1) is prefer ably used alone] under, e.g. 1×10 -2 to 1×10 -4 Torr pressure (at 100-200°C for 30-60min), evaporating and polymerizing the polymaleimide and depositing the polymer on a substrate, such as glass or stainless steel, in a vacuum.