Organosilicon Hybrid Materials Derived From Epoxide‐Functionalized Twin Monomers: Novel Adhesion Promoters for Composites

ABSTRACT The synthesis and characterization of epoxide‐functionalized twin monomers is reported, comprising glycidyl ether and epoxycyclohexane derivatives of 4H‐1,3,2‐benzodioxasiline. The thermal properties of the monomers were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Nanostructured organic–inorganic hybrid materials were obtained by thermally induced twin polymerization of the bulk materials. The formation of a phenolic resin network alongside polysiloxane structures was observed, as evidenced by infrared (IR) as well as solid‐state 13 C and 29 Si nuclear magnetic resonance (NMR) spectroscopy. Additional cross‐linking of the siloxane moieties through the ring opening reactions of covalently bound epoxide groups was confirmed. Furthermore, the influence of curing temperature and 1‐methylimidazole (1‐MI) catalysis on the polymerization behavior was investigated. The catalyzed samples of 2‐methoxy‐ and 2‐methyl‐2‐(3‐glycidoxypropyl)‐4H‐1,3,2‐benzodioxasiline with 1 mol% 1‐MI showed to be the most promising adhesion promoters by exhibiting rapid curing at 180°C. As a proof of concept, their adhesive performance was evaluated by lap‐shear testing for the model system of aluminum alloy EN AW‐6082‐T6 and polyamide 6 (PA6). Lap‐shear strengths of up to 8 MPa were achieved, comparable to a conventional epoxy adhesive based on bisphenol A diglycidyl ether (BADGE).