Toughening aid and modified epoxy resin

The invention discloses a toughening aid and modified epoxy resin, which are prepared by the following steps: step A, carrying out degradation reaction on initial polyurethane and a degradation agent with active groups, breaking at least one part of molecular chains of initial polymers, and preparing a polyol product containing molecular fragments of the initial polymers; and 2, carrying out a ring-opening reaction on the cyclic anhydride and the polyol product to obtain the toughening aid containing carboxyl. In addition, the toughness of the modified epoxy resin prepared by using the toughening aid can be improved. According to the invention, a degraded polyurethane product obtained based on polyurethane is used as a polyol product, and cyclic anhydride is added to carry out a ring-opening reaction with the polyol product, so that a carboxyl-terminated substance is obtained and can be used as a toughening aid component. And the toughening aid component can be added into an acid anhydride cured epoxy system,