A preparation method of a modified bismaleimide resin includes the following steps. Maleic anhydride is mixed with a bisamine compound to obtain a corresponding mixture. The mixture is heated. The bisamine compound has a main chain structure or fragment represented by Formula A, Formula B, or Formula C as described in the description.

In one aspect, the disclosure relates to the use of poly(diethylenepolyamine) derivatives for the extraction of metals, in particular rare-earth metals. In another aspect the disclosure relates to articles and methods for extracting rare-earth metals.