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Methacrylate, acrylate, and styrene polymers with photochromic spiropyran side groups connected to the main chains through spacers of various lengths were prepared by free radical polymerization. The thermal back-reaction of photochemically formed merocyanines to spiropyrans in the polymer and monomer solutions was studied by flash photolysis. The reaction goes much slower in the polymer than in the monomer solutions. The longer the spacer, the higher the reaction rate in the polymers. Increased solvent polarity increases the rate in the polymer solutions and decreases it in the monomer ones. Whereas for polymer solutions in methyltetrahydrofuran the fading fits first-order kinetics, in benzene or toluene the fading kinetics is described by a superposition of two exponential decays. This is ascribed to the presence in the latter solvents of two types of merocyanines that also reveal different absorption spectra. It is proposed that the formation of intramolecular stacks causes these kinetic and spectroscopic effects.

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Photochromic compounds of the phenoxynaphthacenequinone type have been incorporated chemically in three polymers: polystyrene, poly(methy1 methacrylate), and polysiloxane, overcoming grave synthetic problems due to the presence of the quinone group. Contents of up to one photochromic unit per polymer unit could be obtained without impairing the photochromism of the polymers. Interconversion of the two modifications of the photochrome takes place photochemically but not thermally and is completely reversible, both in the free and in the incorporated photochrome.