| http://www.w3.org/ns/prov#value | - Accordingly, optical materials such as lens, which have photochromic function can be directely produced, for example, by adding the photochromic compound or composition to a monomer composition, which provides an optical material by its polymerization, and then charging the resultant mixture in a mold for cast polymerization, whereby the monomer composition is subjected to a polymerization treatme
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