STUDY OF MOLECULAR ORDER IN ORGANO-SOLUBLE POLYIMIDE THIN-FILMS

The changes in refractive indices (n(TE) and n(TM)) in a direction nor mal to the plane of thin films of an organo-soluble polyimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride and 2,2'-dimethyl-4 ,4'-methylene dianiline were measured by a prism coupler. The results implied that the molecules near the substrate-polyimide interface were much ordered, while those near the polyimide-air interface were less ordered, judging from the variation in the level of negative birefring ence with the depth of the films. The molecules are more condensed nea r the substrate surface, as seen by the average refractive index incre asing from the polyimide-air interface to the substrate-polyimide inte rface, which implies that the condensed states of polyimide molecules change gradually in the depth direction. (C) 1997 Elsevier Science B.V .