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Preparation of porous polyimide films by selective decomposition of poly(methyl methacrylate) from PI/PMMA-blended films

A series of porous polyimide (PI) films were prepared by decomposing PI/poly(methyl methacrylate) (PMMA)-blended films at appropriate high temperature for a certain period of time in air. The pore-forming agent, PMMA, was blended with poly(amic acid) (PAA) by in situ blending method. As a thermally labile polymer, PMMA was decomposed first to generate substances with low molecular weight, leaving holes in the original location. Fourier transform infrared (FT-IR) spectra were used to characterize the changes in the chemical structure during the process of preparation of porous PI films. The porous morphology was investigated using field emission scanning electron microscopy. Using FT-IR and thermogravimetric analysis, it was confirmed that PMMA disappeared completely after 4 h at 330°C in air. Thus, porous PI films with major differences between surface and bottom morphologies were prepared successfully. The average pore size of the porous films increased with increasing content of PMMA but was not larger than 1 μm.