The Intrinsic Relationship between the Molecular Structure and Properties of Silicone Rubber and Optimization Strategies
Silicone rubber, as an important class of polymer materials, is widely used in various fields due to its unique properties. Its properties are closely related to its molecular structure. In - depth exploration of the relationship between the two and optimization of the molecular structure based on this are of great significance for improving the properties of silicone rubber and expanding its application scope.
The Molecular Structure Foundation of Silicone Rubber
The main chain of silicone rubber is composed of repeated silicon - oxygen bonds (Si - O). This unique structure endows silicone rubber with many excellent properties. The bond energy of the silicon - oxygen bond is relatively high, about 452 kJ/mol, which is more stable than the common carbon - carbon bond (about 348 kJ/mol). This enables silicone rubber to maintain stable performance in a wide temperature range (-60 °C to 250 °C). For example, in the sealing of high - temperature components of aircraft engines, silicone rubber can withstand high - temperature environments without serious aging. The silicon - oxygen bond has a long bond length and a large bond angle, and the internal rotation barrier of the molecular chain is low, making the molecular chain highly flexible. This gives silicone rubber excellent flexibility and elasticity, allowing it to quickly return to its original shape after deformation. It is often used in the manufacture of various seals and shock - absorbing components.
The side groups have a significant impact on the properties of silicone rubber. Common side groups such as methyl groups can enhance the interaction between molecular chains and improve the chemical stability and hydrophobicity of silicone rubber. The number and distribution of methyl groups on every 100 silicon atoms can change the packing mode of molecular chains, thereby affecting the material properties. When the methyl content is high and evenly distributed, the chemical corrosion resistance of silicone rubber is enhanced, and it can effectively resist the erosion of chemical media in the sealing of chemical pipelines. Introducing special side groups can endow silicone rubber with special properties. Fluorine - containing side groups can significantly reduce the surface energy of the material and improve its weather resistance and chemical corrosion resistance; amino - containing side groups can enhance the compatibility of silicone rubber with polar materials and promote interfacial bonding in the preparation of composite materials.
The Intrinsic Relationship between Molecular Structure and Properties
The Correlation with Mechanical Properties
The mechanical properties of silicone rubber, such as tensile strength and elongation at break, are closely related to its molecular structure. The cross - linking density is a key factor affecting mechanical properties. An appropriate cross - linking density can enhance the interaction between molecular chains and improve the tensile strength. However, if the cross - linking density is too high, the movement of molecular chains is restricted, the material becomes hard and brittle, and the elongation at break decreases. Studies have shown that when the average molecular weight between cross - linking points (Mc) is in a certain range (such as 1000 - 3000 g/mol), silicone rubber can have both good strength and flexibility. The length and distribution of molecular chains also affect mechanical properties. Longer molecular chains and a narrower molecular weight distribution can improve the tensile strength and toughness of the material because the entanglement between long molecular chains is strong, which can effectively transfer stress.
The Correlation with Thermal Properties
In terms of thermal stability, the high bond energy of the silicon - oxygen bond is the basis for the heat resistance of silicone rubber. However, the side groups and cross - linking structure will affect its thermal decomposition temperature. Introducing side groups with good thermal stability (such as aryl groups) can increase the thermal decomposition temperature of silicone rubber. For example, the thermal decomposition temperature of silicone rubber with aryl - containing side groups can be increased by 20 - 30 °C compared with ordinary silicone rubber. The cross - linking structure also affects thermal properties. Appropriate cross - linking can inhibit the thermal movement of molecular chains and improve thermal stability; however, excessive cross - linking may lead to local stress concentration and trigger thermal degradation at high temperatures. The glass transition temperature (Tg) is related to the flexibility of the molecular chain. The main chain structure and the properties of side groups can change the flexibility of the molecular chain, thereby affecting Tg. Side groups with large volume and high rigidity will hinder the internal rotation of the molecular chain and increase Tg; conversely, structures that increase the flexibility of the molecular chain will decrease Tg. For example, introducing flexible spacer groups into the molecular chain of silicone rubber can reduce Tg, enabling it to maintain good flexibility at low temperatures.
Performance Optimization Strategies Based on Molecular Structure
Molecular Structure Design
The properties of silicone rubber can be improved by rationally designing its molecular structure. Introducing heteroatoms (such as nitrogen and phosphorus) into the main chain to form Si - N and Si - P bonds can change the electron cloud distribution of the molecular chain and enhance thermal stability and flame - retardant properties. In the design of side groups, specific functional groups are introduced according to application requirements. In the biomedical field, introducing bioactive side groups (such as polyethylene glycol segments) can improve the biocompatibility of silicone rubber, promote cell adhesion and growth, and be used in the manufacture of artificial organs, tissue engineering scaffolds, etc. In the aerospace field, introducing fluorine - containing side groups can improve the high and low temperature resistance and radiation resistance of silicone rubber to meet the application requirements in extreme environments.
Optimization of Synthesis Process
Improving the synthesis process is crucial for regulating the molecular structure and properties. In the polymerization reaction, precise control of reaction conditions (such as temperature, pressure, catalyst dosage, and reaction time) can achieve precise control of the molecular chain length, molecular weight distribution, and cross - linking density. Using living polymerization techniques, such as anionic polymerization and atom transfer radical polymerization (ATRP), can prepare silicone rubber with a predetermined molecular weight and a narrow molecular weight distribution, improving the uniformity and stability of material properties. In the cross - linking process, appropriate cross - linking agents and cross - linking methods are selected. Peroxide cross - linking can form a uniform cross - linking network, but may produce by - products; hydrosilylation cross - linking has mild reaction conditions and few side reactions, and can prepare high - performance silicone rubber. By optimizing the cross - linking process and adjusting the cross - linking density and cross - linking point distribution, silicone rubber materials with ideal mechanical properties can be obtained.
A deep understanding of the intrinsic relationship between the molecular structure and properties of silicone rubber and the application of molecular structure design and synthesis process optimization strategies can effectively improve the properties of silicone rubber and lay a foundation for its innovative applications in more fields. Future research can further explore new molecular structures and synthesis technologies to promote the development of silicone rubber materials towards high - performance and multi - functional directions.
MY 107 hydroxyl-terminated polydimethylsiloxane V150000-V550000
