Effect of pressure on the water relaxation in glassy polyetherimide

A dielectric study of the water peak in glassy polyetherimide is reported. The peak is found to shift to higher frequency with increasing intensity (associated with increasing water content) and to shift to lower frequency with increasing pressure. The temperature dependence of the peak position is Arrhenius with activation energy 0.46 eV. The activation volume is approximately equal to the Van der Waals b coefficient which is about twice the volume of a water molecule. This implies that the relaxation mechanism involves more than simple reorientation of a water molecule. Modeling results suggest that water molecules can associate with the glassy polymer through hydrogen bonds to the imide carbonyl oxygen atoms. In the case of Ultem® 1000, a water molecule is able to H-bond simultaneously with two carbonyl oxygens, however in Ultem® 5000 the para-bisimide linkage leads to improved chain packing and the more extended geometry allows only one H-bond between each imide carbonyl unit and water molecule.