Surface characterizations of potassium-hydroxide-modified Upilex-S® polyimide at an elevated temperature

Interests in wet-process surface modifications of polyimides have increased because of simplicity and low costs. In this study, Upilex-S®-50 [poly(biphenyl dianhydride-p-phenylene diamine)] polyimide films were initially modified with an aqueous potassium hydroxide (KOH) solution at a relatively high temperature to yield a potassium polyamate surface, followed by acidification to yield a polyamic acid surface. The hydrolysis reaction was confirmed by the Fourier transform infrared attenuated total reflection spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS spectra revealed that potassium polyamate structure could be obtained only by washing the KOH-modified surface with 2-propanol. When the treated surface was rinsed with water, the surface would be partly converted into polyamic acid due to protonation of the carboxylate groups. Atomic force microscopic (AFM) images and AFM cross-sectional analyses revealed large amounts of pinholes on the modified surfaces that might be attributed to the stronger dissolutions of the amorphous regions in the polyimide surfaces.