Biobased Epoxy Resin with Low Electrical Permissivity and Flame Retardancy: From Environmental Friendly High-Throughput Synthesis to Properties

Abstract

Recent years have witnessed significant advances in biobased epoxy resins to replace their petroleum-based counterparts, especially diglycidyl ether of bisphenol A type epoxy resin (DGEBA). However, for meeting a great variety of the requirements, long-standing challenges include environmentally friendly preparation of epoxy resin with few toxic byproducts and improving their properties. Herein, we report a facile method to synthesize new silicone-bridged difunctional epoxy monomers in high yield. They are derived from naturally occurring eugenol by introducing the methylsiloxane and phenylsiloxane linkers of different chain lengths into their molecular backbones. These synthesized liquid epoxy monomers have definitive molecular structure with high purity. These silicone-bridged difunctional epoxy monomers exhibit much lower viscosity (<2.5 Pa s) than commercial DGEBA epoxy (10.7 Pa s) suitable for composites and prepregs. After curing, they exhibit a dielectric permittivity as low as 2.8 and good intrinsic flame retardancy with LOI value higher than 31, far outperforming DGEBA. All these advantages are stemmed from their siloxane-contained segments characterized by low polarity, very high dissociation energy, helical molecular structure, and high molecular volume. Overall, this work provides a very facile and scalable route access to a family of the multifunctional eugenol-based epoxy monomers with low dielectric constant and enhanced flame retardancy.