Two novel eugenol-based difunctional benzoxazines: Synthesis and properties

Two novel eugenol-based difunctional benzoxazine monomers, named E-pea and E-dda, were successfully synthesized with a solvent-less method from eugenol, paraformaldehyde, 4,7,10-trioxa-1,13-tridecanediamine and 1,12-dodecanediamine. Their molecular structures were verified with Fourier Transform Infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Their curing behaviors were studied using differential scanning colorimetry (DSC) and FTIR techniques and a possible polymerization mechanism was proposed. Thermogravimetric analysis (TGA) was adopted to study the thermal stability of two polybenzoxazines, revealing that the fully polymerized E-pea and E-dda (denoted as PE-pea and PE-da) were both fairly thermostable with a char yield of 46.0 wt% at 800 ℃. Finally, contact angle tests manifest that the surface free energy (SFE) of PE-dda film was as low as 16.88 mJ/m2 while that of PE-pea film was 28.56 mJ/m2. Such an obvious increase in PE-pea’s SFE value is mainly caused by the inherent hydrophilicity of ether bonds.