Thermally stable hyperbranched nonlinear optical polyimides using an “A2+B3” approach

To obtain nonlinear optical (NLO) polyimides exhibiting excellent thermal stability and large electro-optical (EO) coefficients, we synthesized a series of novel hyperbranched polyimides from a tris(ether anhydride) [1,1,1-tris[4-(3,4-dicarboxyphenoxy)phenyl]ethane trianhydride (III)] and a difunctional chromophore [(2,4-diamino-4′-(4-nitrophenyldiazenyl)azobenzene) (DNDA)], through ring-opening polyaddition at room temperature to form poly(amic acid)s (PAAs), followed by poling/curing process. The presence of the imide rings in the hyperbranched NLO polymers imparted them with excellent thermal stability. Moreover, their highly hyperbranched architectures resulted in site-isolation effects, which restricted the aggregation of the chromophore units. All of these hyperbranched polymers exhibited larger EO coefficients (14.6–17.2 pm V−1) and better temporal stability at 120 °C than those of linear NLO polymers. In addition, we also observed waveguide properties for hyperbranched NLO polymers (3.4–4.6 dB cm−1 at 1310 nm). Relative to the analogous linear NLO polyimide, the hyperbranched NLO polyimides exhibited superior temporal stability, larger EO coefficients, and lower optical losses.