The transport of water, hydrochloric acid. hydrobromic acid and tetrachloroethylene in poly(ethylene-co-chlorotrifluoroethylene) and polyvinylidene fluoride were studied at 70degreesC by the sorption/desorption technique. The effects on the structure and mechanical properties were studied using size-exclusion chromatography, infrared spectroscopy, differential scanning calorimetry and tensile testing. Solute concentrations in the polymers indicated that both the water and HCl/HBr components diffused into the polymers on exposure to acid solutions. The calculated water contents of the diffusing acids generally differed from the water content in the solution. The ratio of water content in the diffusing acid to that in the surrounding acid solution was generally a function of the relative vapor activity of water and HCl/HBr. It was possible to describe the 35% HCl and 47% HBr desorption data using a two-component model. It was assumed that the water and HCl/HBr diffused separately, each having its own constant diffusion coefficient. The water diffusivity was obtained from the pure water system, and this allowed the HCl/HBr diffusivity to be calculated. It was found that the diffusivity decreased, in a non-simple way, as a function of solute size. The exposure to solute did not lower the molar mass of the polyvinylidene fluoride. Differential scanning calorimetry indicated the development of low-melting point polyvinylidene fluoride crystals during the exposure to all solutes. This seemed to be a consequence of the long-term exposure (175 to 376 days) at 70degreesC. The long-term exposure stiffened several of the polyvinylidene fluoride resins and occasionally made them less ductile. The poly(ethylene-co-chlorotrifluoroethylene) also became stiffer, but it was otherwise unaffected as far as observation by the other available techniques was concerned.