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.

No abstract

No abstract

Photopolymerizations. The monomer compositions were mixed with Irgacure 651 (1% by weight), melted, and aligned between rubbed glass plates separated by a 0.6-mm spacer. The films were submerged 0.5 in. in a thermostated water bath and positioned 9 in. from a 450-W Hg arc lamp for 30 s. Optical and Thermal Measurements. A Perkin-Elmer 552UV/vis spectrophotometer was used to measure the reflectance spectra of the materials as "apparent absorbance". Spectra were measured in the transmittance mode with Nujol in the reference cell. The DSC measurements were recorded with a Du Pont Model 900 thermal analyzer. Mesophase ranges were measured with a Leitz optical microscope using a Mettler FP5 and FP52 temperature control.

No abstract