Improved Flexural Strength of N-Vinyl-Pyrrolidone Modified Acrylic Acid Copolymers for Glass-Ionomers

The flexural strengths of N-vinylpyrrolidone modified glass-ionomer cements were investigated. The optimal molar ratio of the monomers in copolymers, composed of the three components acrylic acid, itaconic acid and N-vinylpyrrolidone, was determined using a SAS statistical program. The copolymers were prepared using a free-radical polymerization process. The viscosities of aqueous solutions of these polymers were determined. Cements were formed by the reaction of these solutions with glass particles. Flexural strength (FS) was used as the basic screening property to find the optimum molar ratio. Statistical models were applied to predict the optimum molar ratios. All strength values were recorded on the specimens conditioned in distilled water at 37°C for 7 days. The optimal molar ratio for these copolymers was 7:1:3 for poly(acrylic acid-co-itaconic acid-co-N-vinylpyrrolidone), based on flexural strength and viscosity. The effect of molecular weight (MW) on FS was also evaluated. Copolymer with a MW of 10, 800 (Mn) showed 85% higher FS than the Ketac-Molar (KM) system, along with a reasonable working viscosity.