Curing chemistry of phenylethynyl-terminated imide oligomers: Synthesis of13C-labeled oligomers and solid-state NMR studies

4-(Phenylethynyl-α,β-13C)phthalic anhydride (PEPA) and 13C-labeled phenylethynyl-terminated imide (PETI) oligomers were synthesized, and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to determine the structure of cured oligomers. Solid-state 13C NMR spectra were collected before and after thermal curing. Using solid-state 13C NMR difference spectroscopy, several cure products were identified. The observed 13C 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.