Role of the in‐plane orientation of polyimide films in graphitization

Abstract

Poly(amide acid) labeled with perylenetetracarboxydiimide (PEDI) was prepared from 3,3Ј,4,4Ј-biphenyltetracarboxylic dianhydride (BPDA), p-phenylenediamine (PDA), and diamino-PEDI. Poly(amide acid) was then reacted with sodium hydride and various kinds of alkyl iodides for transformation into various poly(amide ester)s. The cast films were imidized while fixed on glass substrates to give BPDA/PDA polyimide films. The degree of in-plane molecular orientation (f) of the polyimides and their precursors, poly(amide acid) and poly(amide ester)s, were determined via measurements of the visible dichroic absorption at an incidence angle for a rodlike dye (PEDI) bound to the main chain. All precursor films showed relatively low degrees of in-plane orientation. After imidization of the precursors fixed on glasses, however, striking spontaneous in-plane orientation behavior was observed. The f value for polyimide film from a poly(amide acid) precursor was as high as 0.7-0.8. The f value for polyimide film from a methyl ester precursor, however, was lowered to 0.4 -0.5, but it increased with the increasing size of the alkyl groups. Good correlations of the in-plane orientation of the polyimide films with the tensile modulus of the films and the in-plane orientation of the graphitized films were observed.

Effects of Structural Isomerism and Precursor Structures on Thermo-optic Coefficients of BPDA/PDA Polyimide Films

“…Compared with the P 200 value for the PI from PAA, the smaller P 200 values are obtained for the PIs from PAEs having short chains but larger P 200 values are observed for those with long chains. These results agree with that reported by Takeichi et al [5] who estimated the degrees of molecular orientation using polarized monochromated light. They demonstrated that the molecular orientation is effectively randomized with eliminated alcohols for PAEs having short alkyl chains, whereas the orientation is enhanced in the PAEs having long alkyl chains because eliminated alcohols behave as plasticizers which enhance the in-plane molecular orientation.…”

“…[5] The precursor solutions were spin-coated onto Si (denoted as -c) or BK-7 glass (-d) substrates, followed by drying at 70˚C for 1h. The films were thermally imidized stepwise at 160˚C for 1h, at 250˚C for 1h, and 350˚C for 1h.…”

“…Miwa et al [4] have reported that the CTEs of PI films prepared from PAEs increase as their alkyl chain lengths increase. In addition, Takeichi et al [5] have reported that the degree of in-plane/outof-plane molecular orientation increases with increasing the alkyl chain lengths. These facts suggests that the morphology, packing states, and molecular orientation are appreciably influenced by the isomeric structures of PAA and the alkylchain lengths in PAEs.…”

Polyimide Orientation Layers Prepared from Lyotropic Aromatic Poly(Amic Ethyl Ester)s

“…[22] This procedure leads not only to an orientation at the surface, but to a bulk orientation of the film. The bulk orientation of a perylene chromophore embedded [20] or copolymerized [23] into prepolymer films has been published as well.…”

Characterization of Carbon Films Prepared from Polybenzoxazine Films

“…Especially, carbonization and graphitization of PI were extensively studied because of the molecular design flexibility of PI. The effects of chemical structure of PI [4], cold-drawing of PI film [5][6][7], and constraint during imidization of poly(amide acid) [8] on carbonization and graphitization have been extensively reported on the Kapton type PI, PI(PMDA/ODA) [9], and other PI films [10][11][12][13][14]. It was also revealed that carbonization of PI films give microporous carbon films by thermally treating PI films at 700-900 °C [15,16].…”