Exploration of Poorly Recognized Advantages of Supply Chain Sustainable, Various Aliphatic Multiamine-Based Polybenzoxazines

Aliphatic amine-based viscous benzoxazine resins that are liquid at or near room temperature have great potential for their ease of processability and raw material accessibility, which will play a significant role in large-scale industrial applications. In this study, eight aliphatic benzoxazines are synthesized by the traditional Mannich reaction under solventless conditions using linear diamines, branched diamines, or triamine and cycloaliphatic diamines with eugenol and paraformaldehyde. A recycling sample preparative size-exclusion chromatography (SEC) is used to obtain the purified products. ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy are employed to study the molecular structure of all the aliphatic amine-based benzoxazines. Two exothermic peaks are commonly observed by differential scanning calorimetry (DSC) and are assigned to the oxazine ring-opening and eugenol allyl group polymerization as well as degradation of the allyl group in the eugenol part. The glass transition temperatures (<i>T</i> _g) of all of the aliphatic amine-based polybenzoxazines are evaluated by DSC analysis of the polymers. The activation energy of the polymerization is determined by DSC at different heating rates from 2 to 20 °C/min and calculated by the Kissinger and modified Ozawa methods to be in the range of 102-134 kJ/mol. In addition, the thermal degradation and flammability properties of the polymer are monitored by thermogravimetric analysis (TGA) and microcombustion calorimetry (MCC), respectively. All the monomers showed initial degradation after 250 °C and low flammability with limiting oxygen index (LOI), heat release capacity (HRC), and total heat release (THR) values of 44.8, 77-153 J/g K, and 7.58-20.50 kJ/g, respectively. Among all of the aliphatic amine-based benzoxazines, the cycloaliphatic amine-based benzoxazine (EU-1,2dch) polymers show the best thermal stability and the highest <i>T</i> _g, while tris-functional amine-based benzoxazine (EU-tapa) shows the smallest heat release capacity and the lowest <i>T</i> _g due to their unique structures.