High temperature cure sites for polyimides and related high performance thermosetting systems are important and it has been demonstrated now by several groups that 4-phenylethynylphthalic anhydride and/or 3-phenylethynylaniline are attractive endcappers for polyimides that have wide curing windows and afford solvent resistant networks after 30-90 min at 350-400 degrees C. The present paper has investigated phenylmaleic anhydride (PMA) as an alternate system which is thermally and possibly electron beam curable. Thus, PMA has been successfully utilized as a high temperature crosslinking endgroup for several high performance amorphous polyimides and initial results are described in this paper. Imide oligomers of controlled molecular weights were successfully synthesized by conducting either chemical imidization or by employing a two-step amine-terminated oligomer route followed by endcapping with PMA at about 140 degrees C or lower. The more conventional higher temperature process was complicated by side reactions which are discussed herein. The molecular weights of the oligomers were successfully controlled from 2000 to 15 000 g mol(-1). The materials exhibited about at 200 degrees C curing window between oligomer Tg and cure exotherm. Glass transition temperatures increased by more than 50 degrees C after curing and produced solvent resistant insoluble materials with about 85% gel content. Curing of the phenylmaleimide endgroups was most successful under a nitrogen atmosphere, but it appears that normal moulding operations are acceptable, wherein only moderate amounts of oxygen are introduced into the specimen. The thermosetting reaction appears to be more sensitive to radical initiation than the earlier studied phenylethynyl systems. Dynamic thermogravimetric analysis on the cured PMA functionalized oligomers showed good behaviour and 5% weight loss in air was only observed above 500 degrees C. The systems are being evaluated as structural adhesives and matrix resins for composite materials and excellent titanium/titanium lapshear values of about 5000 psi (34 MPa) on the cured oligomers has been demonstrated.