Abstract
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 poly(urethane-imide) 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 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.
