Epoxy-based polymers functionalized with bisazo chromophores: Synthesis, characterization and photoresponsive behavior

In this work, two series of epoxy-based polymers bearing bisazo chromophores were synthesized from two precursor polymers (BP-AN and BP35-AN) through post-polymerization azo-coupling reactions. The polymers were prepared to contain bisazo chromophores with different electron-withdrawing groups and different numbers of methyl substituents, which were characterized by (1)H NMR, FT-IR, GPC, UV-vis, and thermal analysis. The photoinduced birefringence and surface-relief-grating (SRG) formation of the polymers were studied by irradiating spin-coated films of the polymers with laser light at three different wavelengths (488, 532, and 589 nm). The results show that the polymers containing bisazo chromophores possess broader and red-shifted absorption bands compared with ordinary azobenzene-containing polymers. The electron-withdrawing groups on the bisazo chromophores show significant effect on the absorption band positions. The behavior of photoinduced birefringence and surface-relief-grating (SRG) formation is closely correlated with the chromophore structures and excitation wavelength of the laser light. Both electron-withdrawing groups and methyl substituents on the bisazo chromophores show obvious influences on the photoinduced birefringence growth rate and SRG formation rate. The proper methyl substitution on the bisazo chromophores shows ability to enhance the photoinduced birefringence growth rate, birefringence saturation level, and SRG formation rate. The bisazo polymers obtained in this study can be further explored for applications in telecommunication, data-storage, sensors, and other optical devices. (C) 2011 Elsevier Ltd. All rights reserved.