Linear Phosphazene Chloride‐Catalyzed Ethyl Siloxanes for Silicone Rubber: Trade‐Offs Between Mechanical Strength, Low‐Temperature Flexibility, and Hydrophobicity

The ring‐opening polymerization of 1,3,5,7‐tetramethyl‐1,3,5,7‐tetraethylcyclotetrasiloxane with various capping agents such as 1,1,3,3‐tetramethyldisiloxane, 1,3‐divinyl‐1,1,3,3‐tetramethyldisiloxane, hexamethyldisiloxane, or 1,1,3,3‐tetramethyl‐1,3‐diethyldisiloxane was conducted under the catalysis of acidic linear phosphazene chloride to produce differently functionalized poly(methylethyl)siloxane fluids. Additionally, copolymers containing active SiH bonds and methylethylsiloxane segments were prepared by copolymerizing 1,3,5,7‐tetramethyl‐1,3,5,7‐tetraethylcyclotetrasiloxane with 1,3,5,7‐tetramethylcyclotetrasiloxane. The effects of the capping agent, reaction time, deactivator dosage, and catalyst dosage on the reaction process were investigated. Optimal conditions included a catalyst concentration of 750 ppm and a deactivator dosage five times the catalyst dosage, yielding a lower polydispersity index (PDI = 1.46–1.55) and high production efficiency within 6 h. Silicone rubbers containing MeEtSiO segments were successfully synthesized via hydrosilylation reactions between polymers with active SiH bonds and polysiloxanes with SiCHCH 2 bonds. FT‐IR analysis confirmed the successful hydrosilylation reaction, resulting in the formation of ethyl silicone rubber. Compared to pure methyl silicone rubber, the gel fractions and low‐temperature performance of ethyl‐containing silicone rubber were improved. At the same time, the tensile strength, elongation at break, tear strength, water contact angle, and T g decreased with increasing ethyl content. The mechanism of linear phosphazene chloride‐catalyzed ring‐opening polymerization of 1,3,5,7‐tetramethyl‐1,3,5,7‐tetraethylcyclotetrasiloxane was also explored.