Synthesis and properties of corresponding polymers of urushiol-based benzoxazine monomers modified by silane

Abstract

Polybenzoxazine, a new kind of phenolic materials, have the properties of dimensional and thermal stability and do not release any by-products during its curing process, so polybenzoxazine has shown potential for anti-corrosion coating application. In this study, urushiol, a natural phenol obtained from lacquer, was successfully utilized to synthesize a novel urushiol-benzoxazine monomer (UB) via Mannich-like condensation with paraformaldehyde and triethylenetetramine, then the novel benzoxazine monomers were modified by γ-(2,3-epoxypropoxy)propytrimethoxysilane, the structures of UB and urushiol-benzoxazine modified by silane (UBSi) were characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H NMR spectroscopy, and the results of differential scanning calorimetry (DSC) indicated that the ring-opening polymerization temperature of the benzoxazine modified by silane occurred at approximately 210 °C, lower than that of unmodified benzoxazine. Thermal gravimetric analysis (TGA) measurements showed that the temperatures corresponding to 10 and 50% weight loss (T10 and T50) of UB were 354 and 417 °C, respectively; however, the corresponding values of UBSi were 377 and 436 °C. Strain-stress tests indicated that the failure values of strain and stress of UB were 17.27% and 11.45 Mpa, and the corresponding values of UBSi were 14.82% and 12.21 Mpa, respectively. The water absorption of UB curing coating is 3.75%, while that of UBSi30 curing coating drops to 1.27%.