Study on the synthesis and thermal stability of silicone resins reinforced by Si–O–Ph cross-linking

A novel silicone resin (SR-OH) containing phenolic hydroxyl (Ph-OH) groups was designed and synthesized via co-hydrolysis/condensation and catalytic hydrogenation. During the curing process, the cross-linking degree of the resin was further increased by the Si-O-Ph bonds formed by the reaction of the Ph-OH and terminal Si-OH groups. Thermogravimetric analysis (TGA) showed that the cured resin product exhibited excellent thermal and thermo-oxidative stability, which was much higher than that of a typical methyl phenyl silicone resin (SR-Ph). The temperature at which 5% weight loss occurs (Td5) was up to 606 °C (nitrogen) and 542 °C (air), and its char yield at 800 °C was 91.1% and 85.3% in nitrogen and air, respectively. The significant improvement in thermal stability was mainly attributed to the formation of Si-O-Ph bonds which not only increases the cross-linking degree of the resin but also significantly prevents degradation by the 'back-biting' and oxidative cleavage.