Effect of chemical structure in photochromic polymers of the mercury thiocarbazonate series

The effects of the chemical structure of the functional portion as well as the comonomer composition on the photochromic behavior of vinyl polymers containing mercury thiocarbazonate functional groups in the side chains were investigated. It was found that, for p-acrylamidophenyl mercuric thiocarbazonate polymers, the uses of β-naphthyl and strongly electron-releasing p-methoxyphenyl groups for the thiocarbazone residue provide absorption maxima shifted somewhat to longer wavelengths as compared with the use of unsubstituted phenyl groups, whereas the electron-withdrawing o-trifluoromethylphenyl group brings about much larger shifts towards shorter wavelengths, the o-trifluoromethylphenyl group and those groups capable of exerting steric hindrances such as β-naphthyl and o-methylphenyl groups causing slower light and dark reactions too. The increase of free volumes in the polymers by regulating the comonomer composition, i.e., the lowering of T_g, was found to improve photochromic responses strikingly.