Poly(4,4′-oxydiphenylene pyromellitimide) (PMDA-ODA) and poly(1,4-phenylene pyromellitimide) (PMDA-PDA) polyimides were prepared from poly(amic acid) (PAA) and poly(amic ester) (PAE) precursors, respectively. Water sorption and diffusion behavior in films were measured at 90% R.H. and 25°C using the water sorption method and stress relaxation analysis. Regardless of the method, the diffusion kinetics of water in polyimide thin films was well fitted to Fickian diffusion. For rigid rodlike PMDA-PDA film having high Tg (>400°C), film prepared from PAE precursor with less chain relaxation and poor stacking efficiency induced higher stress relaxation and diffusion coefficient of water than with the PAA precursor. For semi-flexible PMDA-ODA polyimide film, film prepared from PAE precursor having higher ordered arrangement, higher chain orientation, and well packing structure, had relatively lower diffusion coefficient of water and less stress relaxation than with the PAA precursor. Water diffusion and stress relaxation for the rigid rodlike PMDA-PDA films are relatively slower than for the semi-flexible PMDA-ODA films due to morphological differences.
All Science Journal Classification (ASJC) codes
- Polymers and Plastics
- Materials Chemistry