Propargylamine: an attractive amine source for designing high-performance benzoxazine resins with low polymerization temperatures

Abstract

Aniline is a very common amine source for benzoxazine synthesis, but it generally results in relatively high ring-opening polymerization temperatures. The exploration of alternative amine sources to lower the polymerization temperature of benzoxazine resins is a prerequisite for further development of high performance polybenzoxazines. In this work, three propargyl-containing benzoxazine monomers with different numbers of oxazine rings (PH-pa, BA-pa and TH-pa) have been synthesized using phenol/bisphenol-A/1,1,1-tris(4-hydroxyphenyl)ethane, propargylamine, and paraformaldehyde as the starting materials. The structures of these benzoxazines are characterized using NMR, FT-IR and HR-MS spectra, which indicate the successful incorporation of the reactive oxazine ring and the propargyl group into the molecular structure of each monomer. In addition, the polymerization behavior of each benzoxazine has been monitored by in situ FT-IR spectroscopy and differential scanning calorimetry (DSC), which shows that each resin can be completely polymerized through complex polymerization mechanisms including the ring-opening polymerization of the oxazine ring and additional ethynyl polymerization. Moreover, the thermal stability and the flammability of the resulting thermosets have been investigated by thermogravimetric analysis (TGA) and micro-scale combustion calorimetry (MCC), respectively. Notably, the thermoset derived from TH-pa exhibits the highest thermal stability with a peak degradation temperature of 418 °C and a char yield value of 50.2% at 800 °C in nitrogen. It also exhibits the lowest heat release capacity (87.0 J g⁻¹ K⁻¹) and total heat release value (17.4 kJ g⁻¹) among the newly obtained polybenzoxazines.