Reversible optical storage properties of nanostructured epoxy-based thermosets modified with azobenzene units

Abstract

Azo-containing polymers are of particular interest in the design of materials for applications in optical recording. The aim of this contribution was the synthesis and characterization of optically active epoxy-based nanostructured thermosets obtained using epoxidized poly(styrene-b-butadiene-b-styrene) (SBS) as templating agent and modified with azobenzene groups. Morphological analysis by means of atomic force microscopy, as well as an investigation about the anisotropic optical properties of the developed materials was carried out. Different types of morphologies frommicelles without long-range order to nanostructures with long-range order were achieved depending on the content of epoxidized block copolymer and azobenzene, and on the extent of epoxidation of butadiene blocks. In addition, the study of optical anisotropy showed a clear dependence of the optical storage properties upon the concentration of azo-chromophore in the samples. In particular, a thermoset containing 12.3 wt % of azo-dye and 5 phr of SBS with 46 mol % of butadiene blocks epoxidized revealed a spherical micellar morphology with maximum birefringence in the order of 1.8*10-2 and residual fraction of birefringence of around 0.3 after several weeks of turning off the writing beam. Besides, numerous writing-erasing cycles could also be performed without photodegradation of the materials. Furthermore, comparing parent thermosets and nanostructured systems, similar birefringence values were obtained with the advantage that the latter can also be used as templates for the development of multifunctional advanced thermosetting materials with optical properties.