Improvement of aldehyde-functional polybenzoxazine processability and mechanical properties achieved by 5-aminoindole/benzoxazine copolymerization

5-Aminoindole is designed for aldehyde-functional benzoxazine (PHB-a) copolymerization due to the special reaction between the indole and aldehyde groups, and the copolymerization with benzoxazine monomers. The curing and mechanical behavior and thermal properties of the cured resins are investigated using Fourier transform infrared spectroscopy, 1 H NMR spectroscopy, differential scanning calorimetry, scanning electron microscopy, dynamic mechanical analysis, tensile tests and thermogravimetric analysis. The resulting networks show better processability and mechanical properties without obvious degradation in thermal performance. The low curing temperature (70 °C) of PHB-a is achieved after incorporation of 5-aminoindole. An elongation rate of 2.54% and a forcing break of around 72.3 MPa are achieved, while neat poly(PHB-a) is brittle and failed in the grips. Furthermore, its glass transition temperature is maintained up to 234 °C. These findings open a new way to realize low-temperature curing and to improve the mechanical properties of brittle polybenzoxazine resins under the premise of maintaining good thermal stability. © 2020 Society of Industrial Chemistry