Effects of diamines (1,4-phenylene diamine and 4,4′-oxydianiline) on water sorption behavior of polyimide thin film

Several polyimide thin films based on two widely commercialized diamines, 1,4-phenylene diamine (PDA) and 4,4′-oxydianiline (ODA), were prepared from respective poly(amic acid) precursors. Water sorption behavior of the polyimide thin films was gravimetrically investigated. The water diffusion coefficient and water uptake of the PDA based polyimide thin films were in the range of 1.6×10^-10 cm² s^-1 to 12.6×10^-10 cm² s^-1 and in the range of 1.52 wt% to 5.80 wt%, respectively. For ODA based polyimide thin films, the water diffusion coefficient and water uptake were in the range of 3.0×10^-10 cm² s^-1 to 14.9×10^-10 cm² s^-1 and in the range of 1.62 wt% to 2.95 wt%, respectively. The diffusion coefficients of the polyimide thin films are closely related to in-plane orientation, crystallinity, and mean intermolecular distance, whereas water uptake is affected by packing order. PDA based polyimide thin films showed relatively higher degree of crystalline structure, small mean intermolecular distance, and high in-plane orientation than the corresponding ODA based polyimide thin films. This may have caused the lower diffusion coefficient and less water uptake in the PDA based polyimide thin films. PMDA-PDA polyimide thin film showed relatively high water uptake due to poor packing order. The effect of morphology on the water sorption behavior of the polyimide thin films was more significant and may be a critical parameter.