Abstract: Hydroxyl-terminated hyperbranched polyester H20 and H30 with different molecular weights, as well as carboxyl-terminated hyperbranched polyester H20-COOH were used for the toughening of o-cresol formaldehyde epoxy resin. It was found that all the hyperbranched polyesters could improve impact toughness and flexural strengths, and remain flexural modulus of the epoxy resin. The addition of 2.5phr H30 could bring about 90 % increase of impact strength, while flexural strength of epoxy resin could be raised by 60 % with 2.5phr incorporation of H20-COOH. In addition, various hyperbranched polyesters could increase the initial decomposition temperature of the material. There were no evident influences of hyperbranched polyesters on the light transmission of the epoxy resin. With increasing H20-COOH content the water absorption of the epoxy resin decreased.

Key words: epoxy resin, hyperbranched polyester, toughness, light transmission, heat resistance