Two hyperbranched polymers with methyl ester (P1) and epoxy (P2) terminal groups containing pendant azobenzene chromophores were prepared through an "A(2) + B-3" approach used for second-order nonlinear optical materials. Their chemical structures were characterized by NMR and GPC analyses. The polymers have good solubility in common organic solvents and film-forming ability, The pure films were fabricated successively without doping into other matrices. The poled films exhibit high second-harmonic generation coefficients (>50 pm/V) due to the three-dimedsional spatial isolation effect resulting from their highly branched structures. The optical nonlinearity of the poled P2 film is thermally more stable than that of PI due to the cross-linking of epoxy groups with carboxylic acid groups in the former during poling. The onset decay temperature of SHG intensity of P2 was determined to be at around 155 degrees C, which was 20 degrees C higher than that of P1. (c) 2007 Elsevier Ltd. All rights reserved.