Three dendron−linear diblock copolymers with a polyene-type nonlinear optical (NLO) chromophore incorporated in the dendron segment and polystyrene as the linear block were synthesized to investigate the effect of nanostructures on electrooptic (EO) properties. These block copolymers form nanostructures with a periodicity between 36 and 44 nm, which can be characterized using atomic force microscopy (AFM). High EO coefficients (r33) up to 64 pm/V can be achieved in these materials that only have relatively low chromophore concentrations (the highest one is 18 wt %). The resulting poled copolymers also showed good temporal stability. More than 81% of the original r33 value can be retained after being isothermally heated at 85 °C for more than 500 h. On the contrary, the results from the guest−host systems (the chromophore was dispersed into polystyrene) only exhibited lower r33 values and very poor thermal stability (less than 30% of the original r33 values remained after 120 h at 85 °C). These results cle...