The Synthesis of Honokiol‐Based Epoxy‐Siloxane as Toughener for Epoxy Resins

A series of honokiol‐based epoxy‐siloxane (SHEs) was synthesized through Pt‐catalyzed hydrosilylation reactions from honokiol epoxy (HOEP) and terminal hydrogen‐containing silicone oils (HS). The SHEs integrate flexible silicone segments, rigid biphenyl skeletons, and curable epoxy groups distributed on both sides of the main chain, just like a fishbone, resulting in an optimal balance of performance. The SHEs exhibit excellent compatibility with conventional epoxy resins. It was found that the SHEs can significantly increase the performance of epoxy resin in terms of the toughness, water resistance, thermal stability, and dielectric properties. SHEs universally enhance the toughness of epoxy resins cured with various hardeners while largely retaining tensile strength. Notably, with rigid hardener such as cycloaliphatic anhydrides or aromatic amines, the epoxy resins toughened by SHEs showed excellent properties: the elongation at break surges to 17.23% without sacrificing tensile strength, accompanied by an impact strength of 32.52 kJ m −2 , with negligible glass transition temperature (T g ) reduction, high hydrophobicity (the water contact angle is more than 90°). The results demonstrated the feasibility of introducing biobased material honokiol into polysiloxanes to prepare a new high‐efficiency toughener for commercial epoxy resins (DGEBA).