Azo Polymers for Reversible Optical Storage. 5. Orientation and Dipolar Interactions of Azobenzene Side Groups in Copolymers and Blends Containing Methyl Methacrylate Structural Units

Abstract : Two amorphous copolymer series and one blend series based on Disperse Red I and methyl methacrylate are compared using absorption spectra and optically induced birefringence on spin-coated films. Observed blue shifts in the absorption spectra with increasing azo concentration suggest that, locally, azo dipoles are paired antiparallel both intramolecularly and intermolecularly. Induced birefringence studies indicate that the intramolecular dipolar interaction affects the orientability of the azo dipoles. The intermolecular dipolar interaction does not appear to have a large effect on orientability. The dependence of induced birefringence on azo content in the sample is different in the blend series (linear) and in the two copolymer series (nonlinear). A triad sequence distribution model is used to explain this difference. Observed writing efficiencies as a function of composition are also analyzed using a sequence distribution model. Dynamics of the inducing and birefringence relaxation processes are compared using biexponential fitting equations. jg p.2