Optically active polymeric networks containing azobenzene moieties and organic crystals

OROFINO, A.; GALANTE, M. J.; OYANGUREN, P. A.

Lyon

Simposio; Frontiers in Polymer Science - Second International Symposium; 2011

Though the azobenzenes are very promising materials for rewritable holographic recording media, further improvement of the performance, such as the birefringence value, response time, long-term stability (archival life) and durability, is still required for conventional azobenzene materials before they can be used in practical applications. Under these circunstances, we have tried to improve the value of photoinduced birefringence and long-term stability by designing a new azobenzene copolymer. The photoinduced birefringence can be improved in two ways. One is to enlarge the intrinsic molecular birefringence of the azobenzene moiety and the other is to increase the order parameter of the birefringent moiety. To attain long archival life, the glass transition temperature and crystallinity of the material are key factors that should be carefully designed and adjusted. Thus, we have synthesized new azobenzene-containing networks that contain organic crystals, in order to improve the optical performance. The azobenzene units are introduced as photoalignment triggers with good optical response and the organic crystals provide large birefringence, a high order parameter and good stability of the aligned state.A push-pull azo chromophore, Disperse Orange-3 (DO3), was selected as photosensitive reactive. The epoxy monomer was based on diglycidyl ether of bisphenol A (DGEBA) while the aliphatic diamine was m-xilylenediamine (MXDA). Several crosslinked epoxy-based azopolymers containing organic crystals (biphenyl, naphthalene and palmitic acid-based precursors) were synthesized. All of them have a constant chromophore concentration equal to 13 wt % DO3 and variable organic crystal content.The characterization and phase behaviour of the networks, investigated by means of complementary techniques (FTIR, DSC, XRD), has provided us with both molecular and nanoscopic details of the resulting structures. The high values of photoinduced birefringence for low chromophore content, and high remaining birefringence fraction make these materials promising for optical storage applications, switchers, waveguides and second harmonic generation.