Vanillin-Derived High-Performance Flame Retardant Epoxy Resins: Facile Synthesis and Properties

Lignin derivative vanillin when coupled with diamines and diethyl phosphite followed by reaction with echichlorohydrin yields high-performance flame retardant epoxy resins. Biorenewable and environment-friendly flame retardant alternatives to bisphenol A epoxy resins (having plenty of applications such as coatings, adhesives, composites, etc.) have captured great attention due to their ecological and economic necessity. Vanillin, an industrial scale monoaromatic compound from lignin, is a promising sustainable candidate for highperformance polymers, while synthesis of diepoxies is challenging. Meanwhile, bio-based epoxy resins combining high performance and excellent fire resistance are more difficult to be achieved. In this paper, two novel bio-based epoxy monomers EP1 and EP2 were synthesized by one-pot reaction containing Schiff base formation and phosphorus hydrogen addition between vanillin, diamines, and diethyl phosphite, followed by reacting with epichlorohydrin. Their reactivities are similar to bisphenol A epoxy resin DGEBA. After curing they showed excellent flame retardancy with UL-94 VO rating and high LOI of similar to 32.8%, which was due to the outstanding intumescent and dense char formation ability. Meanwhile, it was found that the cured vanillin-based epoxies had exceedingly high T(g)s of similar to 214 C, tensile strength of,similar to 80.3 MPa, and tensile modulus of similar to 2709 MPa, much higher than the cured DGEBA with T-g of 166 degrees C, tensile strength of 76.4 MPa, and tensile modulus of 1893 MPa; the properties of vanillin-based epoxies are easy to be regulated by using different coupling agents diamines during the synthesis process.