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

Abstract

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 m 2 s −1. The diffusion coefficient was found to increase from 1.79 × 10 −13 m 2 s −1 at 303 K to 8.94 × 10 −13 m 2 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 ( r 2 = 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.