Copolymerization of self-catalyzed phthalonitrile with bismaleimide toward high-temperature-resistant polymers with improved processability

Abstract

Phthalonitrile and bismaleimide (BMI) have been considered as high-temperature-resistant materials in the fields of heterocyclic chemistry. In this work, a self-catalyzed phthalonitrile-containing benzoxazine group (BA-Ph) was copolymerized with BMI to prepare high-temperature-resistant polymers with enhanced processability. The underlined chemistry was proposed as the addition reactions between phenolic hydroxyl generated by the oxazine ring opening of BA-Ph and unsaturated imide of BMI. Moreover, differential scanning calorimetry, Fourier transform infrared spectroscopy, and dynamic rheological analysis were used to explore the curing behaviors, structure transition, and processability of the blends. Results indicated that the electrophilic addition reaction between phenolic hydroxyl and BMI was triggered initially, followed by the ring-forming polymerization of nitrile groups catalyzed by the remaining hydroxyl group; the proposed reaction mechanism was verified by using a model compound. Furthermore, the polymerization rate of blends can be well controlled by the relative molar ratio of BA-Ph/BMI, temperature, and time according to the rheological results. Meanwhile, the thermogravimetric analysis showed that all BA-Ph/BMI polymers exhibited good thermal stability ( T5% > 400°C). What is more, mechanical and dielectric properties of BA-Ph/BMI/glass fiber composite laminates were studied indicating that the polymerization of nitrile groups may contribute to the increase in the degree of cross-linking.