Water absorption of poly(methyl methacrylate) containing 4-methacryloxyethyl trimellitic anhydride

The amount of water absorption of poly(methyl methacrylate) (PMMA) containing 0, 1, 3 and 5 wt% of an adhesive monomer, 4-methacryloxyethyl trimellitic anhydride (4-META), was measured at 7°C, 37°C and 60°C. After the water uptake reached equilibrium in specimens, they were desorbed to obtain a constant value and the absorption process was repeated. Mass changes in the second desorption were recorded for the storage temperatures of 37°C and 60°C. Multiple regression analyses were conducted on three independent variables, 4-META concentration, storage temperature and absorption–desorption cycle. A statistically significant relationship was found between the maximum water uptake and 4-META concentration, while there was no relationship between the maximum water uptake and diffusion coefficient obtained using the Fickʹs law. The negative relationship in the latter did not support the free space theory. The significant and positive relationship between the maximum water uptake and 4-META concentration demonstrates that water molecules diffuse through the formation of a hydrogen bond at polar sites. The maximum water uptake was not influenced by temperature, while the diffusion coefficient increased with the rise in temperature. The activation energy was 41–47 and 50–53 kJ/mol in the first and second absorption tests, respectively.