Nail shellacs are a new way of creating long lasting nail color that is durable and chip resistant. The shellac is composed of a photocured polymer similar to that used for dental bonding, known chemically as polymethyl methacrylate. Other names for this polymer include Plexiglass and PMMA. The shellac is made by mixing methacrylate monomers with a benzoyl peroxide initiator followed by exposure to UV radiation causing radical polymerization. The homolytic bond cleavage caused by benzoyl peroxide forms two oxygen radicals that decompose further to carbon dioxide plus a phenyl radical adding one methacrylate double bond. This process repeats until two carbon centered radicals combine over and over again to form the shellac film. The addition of UV radiation rapidly polymerizes film, but the film must be thin for the UV to penetrate. This means that the shellac must be applied in several coats to create the very hard polymer that wears longer than natural nail polish.
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