Curing chemistry of phenylethynyl-terminated imide oligomers:: Synthesis of 13C-labeled oligomers and solid-state NMR studies

4-(Phenylethynyl-alpha,beta-C-13)phthalic anhydride (PEPA) and C-13-labeled phenylethynyl-terminated imide (PETI) oligomers were synthesized, and solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy was used to determine the structure of cured oligomers. Solid-state C-13 NMR spectra were collected before and after thermal curing. Using solid-state C-13 NMR difference spectroscopy, several cure products were identified. The observed C-13 NMR resonances were assigned to four different classes of cure products: aromatics, products from backbone addition (substituted stilbenes and tetraphenylethanes), polyenes, and cyclobutadiene cyclodimers. The effects of postcuring and oligomer chain length on the structure of the cured resins were examined. (C) 2000 John Wiley & Sons, Inc.