. . . "Preferred for use in the fabrication of elements 14 are photopolymers formed by the photo-polymerization of a photoreactive monomer or mixtures of such monomers such as urethane acrylates and methacrylates, ester acrylates and methacrylates, epoxy acrylates and methacrylates, polyethylene glycol acrylates and methacrylates and vinyl containing organic monomers." . .