Molecular Orientation and Photocurrent of Alkyl-Aromatic Polyimide Films Prepared by Vapor Deposition Polymerization

Abstract

Vapor deposition polymerization by a coevaporation of pyromellitic dianhydride and decamethylenediamine monomers has been employed for the preparation of polyamic acid as a precursor for polyimide films. By curing at temperatures of 200–250°C the polyamic acid became the polyimide with directional arrangement of the molecular chain in the normal to the substrate observed by wide-angle X-ray diffraction. The sample containing a large amount of oriented crystals showed a small photocurrent. It was concluded that the oriented chain containing a decamethylene moiety hinders the carrier transfer between pyromellitimide moieties, resulting in a decrease of current.

Evaluation of Molecular Orientation in Aromatic Polyimide Films by FT-IR Reflection Absorption Spectroscopy

“…Orientation of polyimide x1 =sin 27 sin ex+ sin 27 cos a sin f3 (II) sin z2 =sin 27 sin a-sin 27 cos a sin f3( 12) If this configuration of the PI chain describes the average orientation of PI chain, the mean square of cosine of the angle of the segment from the substrate normal, (cos 2 01380 ) can be expressed by a and f3 as following equation.…”

Surface Characterization of Polyamic Acid and Polyimide Films Prepared by Vapor Deposition Polymerization by Using Sum-Frequency Generation

“…Imidization reaction is completed during curing at 200 °C for 1 h in a vacuum. Nonreacted monomers are desorbed from the film or further polymerized to polyamic acid, and a stoichiometric polyimide film is finally formed . The peak at 1500 cm -1 is derived from the aromatic CC stretching mode of the ODA moiety.…”

“…Nonreacted monomers are desorbed from the film or further polymerized to polyamic acid, and a stoichiometric polyimide film is finally formed. 4 The peak at 1500 cm -1 is derived from the aromatic CdC stretching mode of the ODA moiety. This peak remained unchanged or changed only a little (excess ODA), indicating that almost all residual ODA monomers are also polymerized.…”

“…In contrast, vapor deposition polymerization (VDP) process, in which the polymerization reaction proceeds in under vacuum condition without solvent and catalyst, has a number of potential advantages over solvent-based processes . Several works have dealt with VDP-made polyimide films and reported preparation conditions, − electrical properties, interaction of metal with ultrathin polyimide films, − phthalocyanine dispersed in the polymer films, , and preparation of hybrid films of aromatic polyimides . Whereas the structure of VDP-polyimide films has been the subject of a number of investigations, the surface structure of polyimide films has been less extensively examined.…”