Synthesis and properties of low viscosity robust biobased benzoxazine resin

The preparation of biobased benzoxazine resin with low melting point and low curing temperature has important significance for environmental sustainable development and practical application in industrial field. In this paper, biobased benzoxazine monomer HA-fa was synthesized from p-hydroxybenzyl alcohol, paraformaldehyde and furfurylamine, and H-fa were prepared by Mannich reaction of hordenine with paraformaldehyde and furfurylamine. The two benzoxazine organic molecules showed different thermodynamic behaviors. HA-fa and H-fa were liquid at room temperature. The viscosity of HA-fa and H-fa at room temperature (25 degrees C) were 1.683 Pa/s and 0.602 Pa/s, and the curing peak temperature was 220 degrees C and 208 degrees C, respectively, both organic molecules showed excellent processability. Then poly(HA-fa) and poly(H-fa) were prepared by two organic molecules through thermal curing procedure. The comprehensive properties of two benzoxazine resins were investigated. The glass transition temperature (Tg) of poly(H-fa) is 223 degrees C, while the Tg of poly(HA-fa) has two peak temperatures, 225 degrees C and 281 degrees C, respectively. This may be due to the existence of two different cross-linking networks in the resin, which leads to the phase separation of the resin, thus reflecting two Tg. Meanwhile, the initial thermal decomposition temperatures Tdi of poly(HA-fa) and poly(H-fa) were 330 degrees C and 331 degrees C, respectively, showing excellent thermal stability of the newly prepared resin. In addition, poly(HA-fa) and poly (H-fa) have both high storage modulus (3174 MPa and 2608 MPa, respectively, measured at 25 degrees C) and good flexural strength (121 +/- 2.7 MPa and 96 +/- 3.6 MPa). Among the two resins, poly(HA-fa) showed more excellent comprehensive properties, which may be based on the joint action of resin multi-crosslinking sites and hydrogen bond crosslinking network.