Hydrogel contact lenses for extended wear

Abstract From the Canadian patent

Hydrogel Contact Lenses For Permanent Wear A process is disclosed for the preparation of hydrogel contact lenses having improved mechanical properties, said process comprising polymerizing in the, presence of an azo type initiator a monomer mixture, comprising from 25% to 50% by weight of N-vinyl pyrrolidone, up to 5% by weight of methacrylic ar acrylic acid, 0.1 to 1% by weight of 1,3,5-tris(propenoxy)-2,4,6triazine (TPT), or perhydro-2,4,6,-triketo-1,3 5,tris(propene-2)-1,3,5 triazine (TTPT), as a cross-linking monomer, the balance being essentially hydroxy alkyl acrylate or methacrylate, wherein the alkyl group is ethyl or propyl.