Effect of tetraacid on the properties of ODPA/4,4′-ODA polyimide foams

摘要

In this research, a new flexible polyimide (PI) foams was successfully prepared and characterized based on precursor powder foaming. This foams were derived from 3,3',4,4'-oxydiphethalic anhydride (ODPA), 3,3',4,4'-oxydiphethalic tetraacid (ODPA-tetraacid), and 4,4'-oxydianiline (4,4'-ODA). With varying molar percentage of ODPA-tetraacid in (ODPA + ODPA-tetraacid), the changes of properties of PI precursor powders and PI foams were comparatively investigated. The foaming processes of PI foams were observed by a self-made visualization device. The decomposition products of precursor powders were analyzed by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The crystallinity of precursor powders was investigated by wide-angle X-ray diffraction (WXRD). The chemical structure of PI precursor powders and foams was analyzed by FTIR. The thermal properties of PI foams were tested by the methods of dynamic mechanical analysis (DMA), and TG/differential thermogravimetry (DTG) analysis. The cell structure of PI foams was observed by a scanning electron microscopy. The rebound resilience of PI foams was studied by a self-made drop-ball instrument. With the increasing of ODPA-tetraacid, the inflation onset temperatures and inflation degrees of PI foams decreased from 210°C to 118°C and increased from 10 to 14.8 times, respectively. The crystallinity of PI precursor powders increased. The thermal stability of PI foams decreased. The cell structure of PI foams became more uniform and the rebound rates increased linearly. Besides, ODPA-tetraacid did not yield any negative effect on the complete imidization of the PI precursor powder by the FTIR spectra.