Modification of silicone resins by Si–N cross-dehydrocoupling with perfect thermal stability and mechanical performance†
A series of new types of modified hydrosilanes were synthesized, using hydrosilanes and nitrogen heterocycles (triethoxysilane, 2-aminopyrimidine, 1,2,4-triazin-3-amine, benzylamine and 2-aminobenzothiazole), by Si–N cross-dehydrocoupling catalyzed by Ru3CO12. The results of the synthesis were then demonstrated by 1H nuclear magnetic resonance and GPC testing. Furthermore, modified silicone resins were obtained by a hydrolytic condensation reaction catalyzed by tetramethylammonium hydroxide and characterized by TGA, DSC and FT-IR. Next, excellent thermal stabilities were determined (best initial decomposition temperature was approximately 400 °C, T95% was 595 °C, the mass residue rate at 800 °C was 87.2%). Carbon fiber reinforced silicone matrix composites were manufactured according to the technical process developed using DSC and rotary viscometer test results, and the mechanical property (ILSS) showed great improvement from 34.8 to 45.8 MPa because of the modification of Si–N cross-dehydrocoupling. After pyrolysis up to 1000 °C, the composites still showed a superior ILSS value (19.6 MPa) and the modified silicone resins had a more regular and rounded microstructure and appeared to have ceramic-like particles of Si3N4. This work indicated that the silicone resin (Si–N) modified by cross-dehydrocoupling had greater competitiveness in the field of resin matrix composites.