Patent No. 597266 Disclosed is an azo compound of formula I, wherein wherein X1, X2, and X3 independently = H, C1-C6 alkyl, C1-C6 alkoxy, phenoxy, or benzyloxy； Y = H, F, Cl, Br, I, or C1 - C6 alkyl； W = nothing or -O-C(=O)-NH-CH2-CH2-； and Z = H, CH3, C2H51, or CH2OH, such as 2-hydroxy-3-((4-methoxyphenyl)diazenyl)-5-ethylbenzyl methacrylate； 2-hydroxy- 5-methyl- 3-((3,4,5-trimethoxy-phenyl)diazenyl)benzyl methacrylate； and 5-chloro-2-hydroxy-3-((4-methoxyphenyl)diazenyl)benzyl methacrylate.
