Thermogravimetric and calorimetric studies of water absorbed in polyaniline

Abstract

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the behavior of residual water absorbed by an emeraldine base and a salt of chemically synthesized polyaniline (PANI—EB, PANI-ES). The matrix of PANI is shown to contain water molecules participating in both reversible and irreversible absorption. In its turn, the reversibly absorbed water consists of two components. The first component (WD 1) amounts to 5–7 wt.% and is removable from PANI-EB in a flow of dry nitrogen at room temperature. The second one (6–8 wt.%) of more strongly bonded water (WD 2) can be withdrawn from PANI-EB at temperatures from 70 to 150 °C depending on the measurement conditions. Binding energy for WD 2 is about 15–18 kcal/mol. This value exceeds that corresponding to hydrogen bonding. The obtained data are interpreted in terms of chemical interaction of water molecules with PANI chains though hydrolysis of the imine ▪ bond of the polymer.