ULTRATHIN POLYIMIDE FILMS FROM PREFORMED POLYMERS

Multilayer films of preformed polyimide molecules have been obtained f or the first time by the Langmuir-Blodgett technique. The pressure-are a isotherm shows that the polyimide monolayers are strongly dependent on compression rate. The zero-pressure area per repeat unit is about 1 .7 nm(2) when the film is compressed at 100 cm(2)/min. This value is h igher than that expected (1.2 nm(2)) for a closely packed structure. M ultilayers have been investigated with X-ray reflectometry. The thickn ess of a bilayer film is about 4.05 nm, which is between the average b ilayer thickness of a interdigitated multilayer film and that of a bil ayer film containing closely packed backbones and fully extended alkyl side chains. The multilayer films do not display a distinctively peri odic structure. When the films are annealed for a few hours at 180 deg rees C, the structure relaxes somewhat and thickness decreases slightl y.