Thermomechanical Behavior of Biobased Benzoxazine: Structure–Property Relationship and Role of Aromatic Side Groups

Biobased benzoxazine monomers derived from sesamol and monofunctional amines with aromatic side groups were synthesized to study the influence of aromatic side groups on the thermomechanical properties. Furfurylamine is a typical component for biobased benzoxazines and is known to influence the thermomechanical properties of the benzoxazine polymers by increasing the cross-linking density. In this study, the effect of amines similar to furfurylamine on the thermomechanical properties has been investigated. Differential scanning calorimetry analysis was used to analyze the impact of the aromatic side groups on the melting temperature of the monomers, with the pyridine side group having the lowest melting point and onset temperature. All monomers showed cross-linking capabilities to various degrees. Thermogravimetric analysis revealed the thermal stability of the polymers up to 260 °C with less than 5% weight loss and a good char yield of at least 44%. Microcombustion calorimetry data revealed that the peak and total heat release rates decreased with different aromatic side groups, with sesamol furfurylamine-based benzoxazine exhibiting the lowest values. Dynamic mechanical analysis results showed that the furfurylamine and aniline-based polymers exhibited high glass transition temperatures of 220 and 180 °C, respectively. In contrast, the benzylamine-based polymer was mechanically weak and the pyridine-based polymer was extremely brittle, preventing mechanical measurements for these systems. All in all, this study presents various alternatives for furfurylamine, offering promising cross-linking capabilities and subsequent thermomechanical properties.