The Response Mechanisms of the Structure and Properties of Silicone Rubber Materials in Extreme Temperature Environments

Due to their unique chemical structures and physical properties, silicone rubber materials are widely used in many fields. Especially in working conditions facing extreme temperature environments, their performance has received much attention. In-depth research on the response mechanisms of the structure and properties of silicone rubber under extreme temperatures is of great significance for expanding their application scope and improving the reliability of the materials.
In a high-temperature environment, the thermal motion of the molecular chains of silicone rubber intensifies, and the interactions between molecules change, resulting in changes in the structure and properties of the material. When the temperature rises, the vibration of the silicon-oxygen bonds (Si-O) in the molecular chains of silicone rubber intensifies, and the bond length and bond angle change to a certain extent. As the temperature rises further, the degradation and cross-linking reactions of the molecular chains may be triggered. In the high-temperature range with relatively lower temperatures, a moderate cross-linking reaction will increase the hardness and modulus of the silicone rubber because the network structure formed by cross-linking enhances the constraints between the molecular chains and restricts the relative movement of the molecular chains. However, when the temperature is too high, the degradation reaction of the molecular chains dominates, the silicon-oxygen bonds break, resulting in shorter molecular chains and a decrease in molecular weight. This degradation of the molecular chains causes a sharp decline in the mechanical properties of the silicone rubber, manifested as a significant reduction in tensile strength, tear strength, etc., and the material becomes soft and sticky, losing its original service performance. For example, in the high-temperature components of aircraft engines, if the silicone rubber sealing materials are exposed to a high-temperature environment for a long time, there may be a risk of sealing failure due to the degradation of the molecular chains.
In a low-temperature environment, silicone rubber also faces severe challenges. As the temperature decreases, the thermal motion of the molecular chains gradually weakens, and the free volume between molecules decreases. When the temperature drops below the glass transition temperature (Tg), the silicone rubber changes from a high-elastic state to a glassy state, the molecular chains are frozen, and the segmental motion almost stops. At this time, the flexibility of the silicone rubber decreases significantly, it becomes hard and brittle, and its impact toughness and tensile elongation decrease significantly. In some outdoor equipment in polar regions or applications in low-temperature environments in the aerospace field, the low-temperature brittleness of the silicone rubber materials may cause the components to crack when subjected to external impacts, affecting the normal operation of the equipment. Studies have shown that the glass transition temperature of silicone rubber is closely related to its molecular structure. By adjusting the flexibility of the molecular chains, the types and contents of the side groups, etc., the glass transition temperature can be changed, thereby improving the flexibility and service performance of the silicone rubber in a low-temperature environment.
In addition, the influence of extreme temperature cycles on silicone rubber is more complex. During the alternating changes between high and low temperatures, thermal stress is generated inside the silicone rubber material, resulting in repeated stretching and compression of the molecular chains. This cyclic effect of thermal stress accelerates the damage and aging of the molecular chains, making the performance degradation rate of the silicone rubber much faster than that in a single-temperature environment. Studying the response mechanisms of the structure and properties of silicone rubber under extreme temperature cycles helps to formulate reasonable protective measures and life prediction models to ensure the long-term and stable use of the silicone rubber materials in complex temperature environments.


MY R33 HTV phenyl silicone rubber（MePh-chains）