Patent ID: 8236466

Claim:
An erasable medium comprising: a substrate; and a photochromic layer disposed over the substrate, the photochromic layer comprising one or more photochromic molecule-polymer systems, wherein each of the one or more photochromic molecule-polymer systems comprises a photochromic molecule covalently bonded within a polymer main chain as shown below, the photochromic molecule comprising two or more photochromic moieties (PM) linked together via a linker: wherein each polymer chain is a polyalkylmethacrylate, a polycarbonate, a polystyrene, a polysulfone, a polyethersulfone, a polyarylsulfone, a polyarylether, a polyolefin, a polyacrylate, a polyvinyl derivative, a cellulose derivative, a polyurethane, a polyester, a silicone resin, an epoxy resin, a polyvinyl alcohol, a polyacrylic acid, a polystyrene-acrylonitrile, a polyethylene-acrylate, a vinylidenechloride-vinylchloride copolymer, a vinylacetate-vinylidene chloride copolymer, or a styrene-alkyd resin, wherein the photochromic moieties are the same or different, and wherein each of the one or more photochromic molecule-polymer systems has a glass transition temperature in the range of about 30° C. to about 150° C.