Water sorption in a bis(GMA)/TEGDMA resin

Some water sorption-desorption properties of a heat-cured copolymer of bisphenol-A-glycidyl methacrylate/triethylene-glycol-dimethacrylate [bis(GMA)/TEGDMA] were investigated during three sequential water sorption-desorption cycles at 60, 37, and 60 degrees C. The results showed that the investigated polymer absorbed almost one molecule of water for each bis(GMA)/TEGDMA molecule, causing a volumetric expansion slightly smaller than the volume of the absorbed water. The determined mean value of the sorption and desorption diffusion coefficients for a specific cycle, here named the "true" diffusion coefficient, was about 1.5 X 10(-8)cm2s-1 at 60 degrees C, decreasing to one-third of that value at 37 degrees C. Although there were differences in leaching between the two sorption-desorption cycles at 60 degrees C, no differences in true diffusion coefficients were found during the two cycles at that temperature. However, the sorption process proceeded slower than the desorption process during the first cycle, while the opposite occurred during the second cycle. These variations could be an effect of leaching occurring during the first cycle at 60 degrees C and also the effects of induced swelling stresses on the diffusion process.