Polyetherimide oligomers having crosslinking end cap moieties which provide improved solvent-resistance to cured composites are generally represented by the formula: ##STR1## wherein X=--O-- or --S--; ##STR2## n=1 or 2; ##STR3## E=allyl or methallyl; R=a trivalent C.sub.(6-13) aromatic organic radical;R.sub.1 =any of lower alkyl, lower alkoxy, aryl, or substituted aryl;R'=a divalent C.sub.(6-30) aromatic organic radical;j=0, 1, or 2; andG=--CH.sub.2 --, --O--, --S--, or --SO.sub.2 --Blends generally comprise substantially equimolar amounts of the oligomers and a comparable, compatible, noncrosslinking, etherimide polymer of substantially the same backbone. The crosslinkable oligomers are made by reacting substituted phthalic anhydrides with hydroxyaryl amines and suitable crosslinking end cap reactants, or by self-condensation of phthalimide salts followed by capping the polymers. Related polyetherimides of the present invention can be prepared by the condensation of nitrophthalic anhydride, diamines, dialcohols (dihydricphenols), and phenolic, crosslinking end caps (A--OH), or the condensation of bis(phenates) or dialcohols (bisphenols), diamines, nitrophthalic anhydride, and amine-terminated end caps (A--NH.sub.2) or nitro-terminated end caps (A--NO.sub.2).The oligomers and blends can be prepregged, and can be cured to form advanced composites having aerospace applications.