| abstract |
Photochromic composition suitable for use in the manufacture of lenses. It comprises a photochromic compound which has been incorporated into a polymer obtained by polymerization of a polyol(allyl carbonate) of the formula: R'-(O-CO-O-CH 2 -RC = CH 2 )n, wherein n is an integer of from 2 to 5, R is hydrogen or C 1 -C 4 alkyl and R is derived from a non-aromatic polyol containing n hydroxyl groups. To improve fatigue, life and colouring/decolouring speed, the polymer contains in addition 0,01-15% by weight of units derived from a copolymerizable compound containing an aromatic constituent, such as styrene, divinyl benzene, benzyl methacrylate or triallyl cyanurate. |