A study of the effect of absorbed water on the T_g of a poly(amideimide) using DMA and DSC

The absorption by and diffusion of water in a commercially available poly(amideimide), Torlon^® 4203, and the dependence of the glass transition temperature (T_g) of this polymer on the weight % absorbed water have been investigated. Diffusion studies indicated that the activation energy for the diffusion process of water in this poly(amideimide) was 44.2 kJ mol^-1 and that the permeability index was 1.17 × 10^-5 m² s^-1. The diffusion coefficient was found to increase from 1.79 × 10^-13 m² s^-1 at 303 K to 8.94 × 10^-13 m² s^-1 at 333 K. The T_g of the polymer, as determined from dynamic mechanical analysis (DMA), was found to decrease monotonically from 568 to 477 K as the weight % absorbed water in the polymer was increased from 0% to 4.25%. Linear least-squares analysis of the data indicated that the relationship between T_g and weight % absorbed water (W_%Aw) was given by T_g = 576.4 - 22.0 W_%AW (r² = 0.990). T_g studies using differential scanning calorimetry (DSC) indicated that the diffusion of water from the sample had a major effect on correlations between T_g and % absorbed water. That is, at low heating rates absorbed water diffused from the sample before the sample was heated to the glass transition temperature and therefore the measured T_g was similar to that for a dry sample. The effect of absorbed water on the dimensional stability of this polymer when heated rapidly to temperatures in the vicinity of the glass transition temperature is also discussed.