Catalyzing the Ring-Opening Polymerization of 1,3-Benzoxazines via Thioamide from Renewable Sources

The high curing temperature of benzoxazines is an important concern for production materials under benign conditions via autoclave curing, which limits industrial applications of these resins as high-performance polymers. Thioamide as a catalyst to lower the ring-opening polymerization (ROP) temperature of simple 1,3-benzoxazines was synthesized from renewable compounds such as furfural and furfurylamine by using the Willgerodt-Kindler reaction. Differential scanning calorimetry studies revealed that the observed reducing effect is more pronounced for onset curing temperatures and as much as 48 °C reduction is noted. Moreover, the catalytic performance of the thioamide could be enhanced by mixing with Cu(II) benzoate. The latent character of the catalyst system was confirmed by NMR and Fourier transform infrared spectroscopy. Moreover, thermal stabilities of the catalyzed polybenzoxazines were analyzed and compared to uncatalyzed polybenzoxazines, and an apparent char yield increment was observed for all the catalyzed samples.