Method for making photochromic contact lenses

A method for producing photochromic contact lenses, comprising the steps of:

• (1) obtaining a first polymerizable fluid composition, wherein the first polymerizable fluid composition is free of any polymerizable or non-polymerizable photochromic compound and comprises (i) at least one polymerizable material, (ii) at least one first free-radical initiator, and (iii) at least one iniferter;
• (2) introducing the first polymerizable fluid composition into a lens mold, wherein the lens mold comprises a male mold half having a first molding surface and a female mold half having a second molding surface, wherein the male and female mold halves are configured to receive each other such that a mold cavity is formed between the first and second molding surfaces and the first polymerizable fluid composition is enclosed in the mold cavity when the mold is closed;
• (3) curing thermally or actinically the first polymerizable fluid composition in the mold cavity of the lens mold to form an unprocessed contact lens having a crosslinked polymer network with iniferter moieties covalently attached thereto;
• (4) separating the lens mold into the male and female mold halves, with the unprocessed contact lens adhered onto a lens-adhered mold half which is one of the male and female mold halves;
• (5) applying a second polymerizable fluid composition onto a central circular region on the surface of the unprocessed contact lens adhered on the lens-adhered mold half, wherein the second polymerizable fluid composition comprises (iv) at least one photochromic vinylic monomer and (v) at least one second free-radical initiator;
• and
• (6) after the second polymerizable fluid composition has penetrated and diffused into the crosslinked polymer network, initiating iniferter-induced polymerization of the second polymerizable composition to graft said at least one photochromic vinylic monomer onto the crosslinked polymer network, thereby obtaining an unprocessed photochromic contact lens having a central photochromic zone that has a diameter of about 13 mm or less and is concentric with the central axis of the unprocessed photochromic contact lens and capable of undergoing reversible change from a colorless or light-colored state to a colored state upon exposure to UV/HEVL radiation.