The preparation and properties of a highly cross-linked dibutyl phthalate-modified methyl methacrylate polymer are described. The material is virtually optically isotropic with a refractive index near 1.5 and exhibits low absorption in the wavelength region 3000 Å to 2 µ. It exhibits good dimensional stability when properly annealed and can be easily polished to close optical tolerances. It is unaffected by many organic and inorganic solvents. Careful preparation and annealing have removed gross density gradients and adventitious particle scattering in the medium.
David L. Stockman and Raymond A. Shirk, "On the Preparation and Properties of an Optically Isotropic Polymer," Appl. Opt. 5, 863-867 (1966)