COMPARISON OF WATER SORPTION BY METHACRYLATE AND DIMETHACRYLATE MONOMERS AND THEIR CORRESPONDING POLYMERS

Water sorption of some glycol dimethacrylate and methyl methacrylate monomers was determined by Karl Fischer analysis. After gamma-irradiation, the corresponding polymers were characterized in terms of percentage water uptake (gravimetrically), diffusion coefficient (D), and contact angle (theta) measurements. Water sorption of the polymers approximated Fick's law. Ignoring the double bond contribution, the weight per cent oxygen content (WPO), which is indicative of hydrophilic character of these materials, was calculated and correlated with the total oxygen content present in each monomer molecule. A linear relationship between the WPO and percentage water uptake was observed in a series of four glycol dimethacrylate and eight linear methyl methacrylate monomers. Their corresponding polymers conformed to a linear correlation between the WPO and theta. On the basis of its WPO, one dimethacrylate monomer (BIS-GMA) sorbed less water than expected because an intramolecular hydrogen bond was present. The rapid initial rates observed in soft methyl methacrylate polymers were attributed to the water soluble impurities present in the matrix. The D values of the networks based on difunctional methacrylates were generally lower than methyl methacrylates, presumably because of the highly crosslinked nature of the former.