Comparison between nadimide and 1,2,3,6-tetrahydrophthal-imide end-capped resins, preparation and thermal behaviour

Nadimide and tetrahydrophthalimide end-capped oligomers have been synthesized from a mixture of para- and meta-phenylenediamine, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (HFDA) and nadic or tetrahydrophthalic anhydride. Several percentages (25 to 50%) of metaphenylenediamine were used to obtain end-capped oligomers soluble in N-methylpyrrolidone. The tetrahydrophthalimide end-capped resins were characterized by H-1 nuclear magnetic resonance and size exclusion chromatography; their rheological behaviour was compared to their nadimide analogues. As expected from statistics both nadimide and tetrahydrophthalimide end-capped oligomers exhibit similar polydispersity ratios, with a high proportion of diimides which do not contain the HFDA moiety. However, their thermal treatments lead to different behaviours. Bis-nadimides gave crosslinked insoluble materials and bis-tetrahydrophthalimides gave soluble materials in spite of the disappearance of their olefinic protons. (C) 1998 Elsevier Science Ltd. All rights reserved.