PHOTO-INDUCED DICHROISM AND SURFACE-RELIEF-GRATINGS OF HYPERBRANCHED AZO POLYMERS SYNTHESIZED BY AZO-COUPLING REACTION

Abstract

A novel hyperbranched azo precursor polymer containing electron donor-acceptor type azobenzene chromophores was synthesized by step-growth polymerization of an AB_2 monomer,di[2-(N-ethylanilino)ethyl]-5-aminoisophthalate,through azo coupling reaction.The hyperbranched precursor polymer was then reacted with the diazonium salts of 4-amino benzonitril to introduce another kind of donor-acceptor azo chromophores in the peripheral groups.The structure and properties of the azo polymers were characterized by the spectroscopic methods and thermal analysis.The photo-induced dichroism of the hyperbranched polymer was studied and the orientation order parameter of the polymer was estimated to be 0.063.Thin films of the hyperbranched azo polymers were used to fabricate surface-relief-gratings(SRGs) by exposing the thin films to an interference pattern of Ar~+ laser beam at modest intensities(150 mW/cm~2).The azobenzene chromophore introduced by post-azo-coupling reaction in the para-positions of the terminal azobenzene units shows a significant effect on the SRG inscription rate.The hyperbranched azo polymers can potentially be used for applications such as reversible optical data storage,photoswitching,sensors,and other photo-driven devices.