Homogeneous radiopaque polymers with organobismuth compounds

The effectiveness of triphenylbismuth and a few other bismuth compounds for use as a radiopacifying (X-ray contrast) additive in polymeric materials was tested. Ph3Bi was found to be compatible (sometimes up to 70 wt %) with a wide range of monomers and polymers. It yields homogeneous mixtures with polystyrene, poly(vinyl chloride), polyacrylates, polyethylene, and other polymers. They can be formed by solvent casting, by melt processing, or by polymerizing a Ph3Bi/monomer mixture. Polymerization is not affected by the presence of Ph3Bi even when amine accelerators are used. Radiopacities of the polymer mixtures are proportional to the molar content of Ph3Bi, and can easily exceed that of aluminum. The bismuth compound lowers the Tg of PVC, PMMA, and polystyrene by 1.3°C/wt % Ph3Bi. The additive is moisture-insensitive, water-insoluble, and heat-stable. It does not leach into water and has a low toxicity index. Leaching even in organic solvents can be prevented entirely by covalently binding bismuth to the polymer matrix through the use of monomers such as styryldiphenyl bismuth.