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 degrees 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. (C) 2011 Elsevier BM. All rights reserved.