The preparation of copolymers of methyl methacrylate and various metal methacrylates is described. The metals studied are lead, barium, calcium, and strontium. Lead and barium in particular improve many of the properties of PMMA. For instance, sensitivity to electrons and x rays is increased by a factor of approximately 3. Flow temperature is raised and chemical etch resistance is improved. Lead gives the most improvement followed by barium then strontium then calcium. The lead concentration at which the maximum contrast is obtained is 3 wt %.