Liquid EtO-POSS promoted silicone resin primer with enhanced adhesion, thermal stability and flame-retardancy

In the aerospace field, silicone resin (SR) primers face challenges such as insufficient adhesion, limited thermal stability, and poor flame-retardancy. To overcome these drawbacks, a liquid highly reactive octaethoxylated polyhedral siloxanes (EtO-POSS) was developed via a thiol-ene click reaction then introduced into SR to construct a covalently cross-linked three-dimensional organic-inorganic hyperbranched network. This strategy utilizes the hydrolysis-condensation reaction between the ethoxyl groups on EtO-POSS and alkoxy groups of the resin, together with the hydroxyl groups on the metal substrate surface, to form strong chemical bonds at the interface, thereby enhancing the primer's mechanical strength, interfacial adhesion, and thermal stability. The results show that with 4 wt% EtO-POSS, the EtO-POSS@SR composites achieves a tensile strength of 3.49 MPa and an adhesive strength of 2.22 MPa, which increase 39% and 48% compared with pure SR, respectively. At an addition rate of 10 wt%, the flame retardancy rating reaches UL-94 V-0. Besides, the possible mechanism was proposed by investigating the combustion residues of EtO-POSS@SR composites. Thus, this work provides a feasible molecular design and strategy for developing high-performance and multifunctional silicone resin primers for potential applications. Download: Download high-res image (243KB) Download: Download full-size image