Synthesis of amino-terminated hyperbranched polysiloxane toughener and its application in CF/EP composites

Hyperbranched polymers are well-established for boosting the toughness of epoxy-based systems. In this work, a novel amino-terminated hyperbranched polysiloxane (HBPSi-NH₂) was synthesized and then incorporated into carbon fiber/epoxy (CF/EP) composites to improve their mechanical performance. A two-step synthetic route was involved: linear epoxy-terminated polysiloxane (LDP) was initially prepared as the intermediate, and the target HBPSi-NH₂ was then obtained via nucleophilic addition between LDP and diethylenetriamine. Structural characterization via FTIR and ¹H NMR demonstrated that target HBPSi-NH₂ was obtained, while quantitative analysis based on ¹³C NMR data showed that the degree of branching of the product was 0.78. The influence of adding HBPSi-NH₂ as a toughener to bisphenol A epoxy resin (E51) blends was systematically investigated. The incorporation of 3 wt% HBPSi-NH₂ marginally reduced tensile and flexural strengths of the toughened epoxy. However, it significantly enhanced the impact strength from 26.7 kJ m^-2 to 56.2 kJ m^-2. Incorporating the toughener into CF/EP composite fabrication effectively improves tensile strength, flexural strength and short-beam shear strength, especially with low HBPSi-NH₂ amounts (3 and 5 wt%). This study offers a facile strategy to simultaneously improve the mechanical strength and interfacial properties of CF/EP composites.