IMPROVED FLEXURAL STRENGTH OF N-VINYL-PYRROLIDONE MODIFIED ACRYLIC-ACID COPOLYMERS FOR GLASS-IONOMERS

The flexural strengths of N-vinylpyrrolidone modified glass-ionomer ce ments were investigated. The optimal molar ratio of the monomers in co polymers, composed of the three components acrylic acid, itaconic acid and N-viaylpyrrolidone, was determined using a SAS statistical progra m. The copolymers were prepared using a free-radical polymerization pr ocess. The viscosities of aqueous solutions of these polymers were det ermined. Cements were formed by the reaction of these solutions with g lass particles. Flexural strength (FS) was used as the basic screening property to find the optimum molar ratio. Statistical models were app lied to predict the optimum molar ratios. All strength values were rec orded on the specimens conditioned in distilled water at 37 degrees C for 7 days. The optimal molar ratio for these copolymers was 7:1:3 for poly(acrylic acid-co-itaconic acid-co-N-vjnylpyrrolidone), based on f lexural strength and viscosity. The effect of molecular weight (MW) on FS was also evaluated. Copolymer with a MW of 10,800 (M-n) showed 85% higher FS than the Ketac-Molar (KM) system, along with a reasonable w orking viscosity.