The facile synthesis and optical nonlinearity of hyperbranched polyaspartimides with azobenzene dyes

A series of thermally stable nonlinear optical hyperbranched polyaspartimides were synthesized via the Michael addition reaction of a fluorine-containing trimaleimide, 1,1-tris[4-(4-maleimide-2-trifluoromethyl-phenoxy)-phenyl]ethane and two respective azobenzene dyes, namely bis(4-aminophenyl(4-(4-nitrophenyl)-diazenyl)phenyl)-amine and 2,4-diamino-4′-(4-nitrophenyl-diazenyl)-azobenzene, using p-toluenesulfonic acid as catalyst. The incorporation of fluorine-rich components within the hyperbranched polymers increased solubility in organic solvents and reduced optical loss. Owing to the three-dimensional, void-rich, topological structure of the highly branched polymers, the spatial separation of the dyes endows the polymers with a favorable site isolation effect, which thereby negates chromophoric aggregation. Using in situ contact poling, electro-optical coefficients, r₃₃ of 6.5–14.7 pm V^?1 and temporal stability at 80 °C were obtained. Both the dynamic thermal and temporal stabilities of the hyperbranched polyaspartimides were superior to those of their linear analogues.