Probing the copolymerization of alkynyl and cyano groups using monocyclic benzoxazine as model compound

Aromatic heterocyclic polymers play key roles in high performance polymers. Among the various unsaturated functional groups, alkynyl and cyano groups stand out because they may form rigid and thermally stable six-membered rings such as benzene and triazine rings. In this work, monocyclic benzoxazine is used as a platform to integrate the alkynyl and/or cyano groups and the polymerization of these compounds are studied in detail. The curing behavior is investigated by differential scanning calorimetry (DSC), the chemical structures of the polymers are studied by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Moreover, the thermal and dielectric properties of the polymers are also probed. It is found that trimerization of alkynyl groups occur more easily than cyano groups. As the ratio of the two functional groups varies, pyridine rings can be formed more easily than pyrimidine rings. Moreover, more cyano groups may lead to reduction of glass transition temperature (Tg) because of the low reactivity of cyano groups, but formation of pyridine rings could greatly improve the thermal stability of the polymer and char yield could reach 69%, which is much higher than the other polybenzoxazines prepared in this work.