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Porous polyimide films were prepared in two steps. The first step was the preparation of poly(urethane-imide) films by a reaction between a phenol-terminated polyurethane prepolymer and poly(amide acid) obtained from pyromellitic dianhydride (PMDA) and oxydianiline (ODA) followed by thermal treatment at 200 • C. The second step was the pyrolysis of the poly(urethaneimide) films. Upon thermal treatment of the poly(urethane-imide) films at 300 to 400 • C, the thermally less stable urethane domains decomposed, leaving porous polyimide films. The presence of pores was confirmed from the scanning electron microscope (SEM) picture of the surface and the cross section of the films. The size distribution of the pores was narrow. With increasing urethane content, the apparent density decreased but the size of the pore did not increase so much. Instead, the number of pores increased. Tensile measurements revealed that, with increasing urethane component the tensile modulus did not vary very much, but the elongation and thus the tensile strength decreased. Viscoelastic analyses showed that all the porous polyimide films had a high glass transition temperature, above 400 • C, and storage moduli were maintained up to 400 • C.

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.

Porous polyimide films were prepared by 2 steps. The first step is the preparation of poly(urethane-imide) films by a reaction between phenol-terminated polyurethane prepolymer and poly(amide acid).Polyurethane prepolymer was prepared from the reaction of polyethylene adipate and hexamethylenediisocyanate. Poly(amide acid) was obtained from pyromellitic dianhydride and oxydianiline. The second step is the pyrolysis of the polyurethane-imide) films. Upon thermal treatment of the polyurethane-imide) films at 300 to 400°C, the thermally less stable urethane domains decomposed, leaving porous polyimide films. The presence of pores was confirmed from the scanning electron microscope of the surface and the cross-section of the films. The size distribution of the pore was narrow. With the increase of urethane content, the size of the pore increased. Tensile measurements revealed that, with the increase of urethane component, tensile modulus did not vary so much, but elongation and thus tensile strength decreased. Viscoelastic analyses showed that all the porous polyimide films had high glass transition temperature at above 400°C, and storage moduli were maintained up to 400°C.

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