Optical coating having low refractive index

#The present invention is directed to transparent and low refractive index optical coatings for use in light transmitting electronic devices. In particular, the present invention is directed to low refractive index optical coatings manufactured from hydrogels.

#By definition, a hydrogel is a polymeric material which exhibits the ability to swell in water and retain a significant fraction, (e.g., greater than 20%) of water within its structure, but which will not dissolve in water. The hydrogel forms an equilibrium state with water, and maintains its equilibrium shape. Included in this definition are a wide variety of natural materials of both plant and animal origin, materials prepared by modifying naturally occurring structures, and synthetic polymeric materials.

#Synthetic hydrogels include polyacrylic acid, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylamide, polyhydroxybutyl acrylate and methacrylate, polyhydroxyethyl acrylate and methacrylate, polyethylene oxide and polyurethane. Hydrogels with various equilibrium content of water are known and used for manufacturing soft contact lenses and for medical applications such as wound dressings and adhesives for biomedical electrodes.

#A mixture consisting of 1.0 gram of polyethyleneglycol (9) diacrylate and 1.0 gram of methoxypolyethyleneglycol (9) acrylate was polymerized with 0.25 wt. % sodium persulfate and 0.25 wt. % of sodium metabisulfite (by weight of the monomers) in 38.0 grams of deionized water for about 16 hours at ambient temperature. The resulting hydrogel after swelling contains 93.5 wt. % of water and has a refractive index of 1.3388.

#A mixture consisting of 2.0 grams of polyethyleneglycol (9) diacrylate and 2.0 grams of methoxypolyethyleneglycol (9) acrylate was polymerized with 0.15 wt. % sodium persulfate and 0.15 wt. % of sodium metabisulfite (by weight of the monomers) in 36.0 grams of deionized water for about 16 hours at ambient temperature. The resulting hydrogel after swelling contains 89.6 wt. % of water and has a refractive index of 1.3455.

#A mixture consisting of 3.0 grams of polyethyleneglycol (9) diacrylate and 3.0 grams of methoxypolyethyleneglycol (9) acrylate was polymerized with 0.15 wt. % sodium persulfate and 0.15 wt. % of sodium metabisulfite (by weight of the monomers) in 34.0 grams of deionized water for about 16 hours at ambient temperature. The resulting hydrogel after swelling contains 84.5 wt. % of water and has a refractive index of 1.3557.