PHENYLMALEIMIDE ENDCAPPED ARYLENE ETHER IMIDE OLIGOMERS

High temperature cure sites for polyimides and related high performanc e thermosetting systems are important and it has been demonstrated now by several groups that 4-phenylethynylphthalic anhydride and/or 3-phe nylethynylaniline are attractive endcappers for polyimides that have w ide curing windows and afford solvent resistant networks after 30-90 m in at 350-400 degrees C. The present paper has investigated phenylmale ic anhydride (PMA) as an alternate system which is thermally and possi bly 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 syn thesized by conducting either chemical imidization or by employing a t wo-step amine-terminated oligomer route followed by endcapping with PM A at about 140 degrees C or lower. The more conventional higher temper ature process was complicated by side reactions which are discussed he rein. The molecular weights of the oligomers were successfully control led from 2000 to 15 000 g mol(-1). The materials exhibited about at 20 0 degrees C curing window between oligomer Tg and cure exotherm. Glass transition temperatures increased by more than 50 degrees C after cur ing and produced solvent resistant insoluble materials with about 85% gel content. Curing of the phenylmaleimide endgroups was most successf ul under a nitrogen atmosphere, but it appears that normal moulding op erations are acceptable, wherein only moderate amounts of oxygen are i ntroduced into the specimen. The thermosetting reaction appears to be more sensitive to radical initiation than the earlier studied phenylet hynyl systems. Dynamic thermogravimetric analysis on the cured PMA fun ctionalized 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. Copyright (C) 1996 Els evier Science Ltd.