Humid aging of polyetherimide. I. Water sorption characteristics

Abstract

The sorption and desorption kinetics of water into polyetherimide (ULTEM 1000) were studied at various temperatures ranging from 20 to 100°C. The water equilibrium concentration increases slightly with temperature from 1.39% (by weight) at 20°C to 1.50% at 100°C. The solubility coefficient, S, calculated from these data, and the water vapor pressure decrease with temperature. The calculated heat of dissolution Hs is close to −43 kJ mol−1, which explains the low effect of temperature on the equilibrium concentration. The diffusion coefficient, D, varies from about 1.10−12 m2 · s−1 at 20°C to about 16.10−12 m2 · s−1 at 100°C. The apparent activation energy of diffusion, ED, and the heat of dissolution, Hs, of water in the polymer have opposite values (respectively, +43 and −42 kJ · mol−1). From this observation and a comparison of these data with water diffusion characteristics in other glassy polar polymers, it is hypothesized that the transport rate of water is kinetically controlled by the dissociation of water–polymer complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1439–1444, 2000