Diffusion and sorption of water vapor by polyamide‐imides

The study of sorption and diffusion characteristics of glassy polymers based on polyamide‐imides was carried out using the methods of static sorption, dilatometry, electron microscopy. Water sorption isotherms of polyamide‐imides based on trimellitimido‐N‐acetic acid (PAI‐A) and trimellitimido‐N‐p‐benzoic acid (PAI‐B) with different intramolecular ‘hinges’ in the diamine fragment were obtained. The isotherms are S‐shaped and occupy an intermediate position between polyheteroarylenes and aliphatic polyamides. The dual sorption model was used to interpret the results. It is shown that the Langmuir component of the isotherms is determined by the thermal prehistory of glassy polymers, while the sorption component associated with water dissolution according to Flory‐Huggins is determined by the chemical nature of the functional groups included in the monomeric unit. The diffusion coefficients of water and the temperature and concentration dependences of the diffusion coefficients of sorbed water molecules were determined.