Large free volume biobased benzoxazine resin: Synthesis and characterization, dielectric properties, thermal and mechanical properties

High heat resistance, low dielectric constant and low dielectric loss benzoxazine resin is of great significance to the practical application of information industry. In this article, two biobased benzoxazine monomers HA-dea and H-dea were prepared by mannich reaction using p-hydroxybenzyl alcohol and hordenine as phenol sources and 1,10-diaminodecane as amine sources. The two benzoxazine monomers showed different thermodynamic behaviors. The melting point of HA-dea was 77.5 °C, while H-dea was liquid at room temperature, the viscosity of H-dea at room temperature (25 °C) was 5.517 Pa/s. The curing peak temperatures of the two monomers were 217 and 193 °C, respectively. Both monomers showed excellent processability. Two benzoxazine resins poly(HA-dea) and poly(H-dea) were prepared through thermal curing procedure, and the comprehensive properties of two benzoxazine resins were investigated. The glass transition temperatures (Tg) of poly(HA-dea) and poly(H-dea) were 267 °C and 233 °C, respectively, showing excellent heat resistance of the newly prepared resin. Moreover, poly(HA-dea) and poly(H-dea) have both high storage modulus (3341 MPa and 3124 MPa, respectively, measured at 25 °C) and good flexural strength (109 ± 3.6 MPa and 101 ± 3.8 MPa). Moreover, the resins poly(HA-dea) and poly(H-dea) also have low dielectric constant and dielectric loss at 1 MHz, the dielectric constants are 2.78 and 2.56, respectively, and dielectric losses are 0.018 and 0.016, respectively. Among the two resins, poly(HA-dea) exhibits more excellent heat resistance, which may be based on the multi-crosslinking sites and hydrogen bond crosslinking networks.