Thermal Stable and Flexible Bio-Based Polybenzoxazine with Epoxy-Functionalized Poly(dimethylsiloxane) Hybrids

In this study, a monofunctionalized bio-based benzoxazine monomer (VAnBZ-CN) is synthesized by condensation of vanillin, formaldehyde, and aniline, and a bifunctional epoxy-functionalized poly(dimethylsiloxane) (PDMS-epoxy) is also prepared through hydrosilylation reactions with allyl glycidyl ether. By blending the inorganic PDMS-epoxy with the VAnBZ-CN benzoxazine monomer, an organic/inorganic hybrid material is formed, which exhibited enhanced thermal stability after thermal curing polymerization. The improved thermal stability observed in the hybrid material can be attributed to a combination of the formation of the triazine structure by VAnBZ-CN and the presence of the inorganic part of PDMS-epoxy on the surface. For example, the PDMS-epoxy/VAnBZ-CN = 1/1 hybrid showed the thermal decomposition temperature (T_d10) of 309 °C, the glass transition temperature (T_g) of 165 °C, and the char yield of 54 wt.% after the thermal curing polymerization process conducted at 240 °C based on thermogravimetric (TGA) and dynamic mechanical analyses (DMA). Furthermore, the char yield of the hybrid material with PDMS-epoxy/VAnBZ-CN = 1/3 is higher than that both of pure VAnBZ-CN and PDMS-epoxy after the thermal curing polymerization process. This result indicates that the addition of PDMS-epoxy resin can improve the formation of a char residue and then enhance the resistance to thermal decomposition for their overall thermal stabilities.