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There are a wide variety of raw materials used in polyurethane elastomers; the composition and arrangement of groups within their macromolecular structures are complex. Moreover, there are numerous methods for synthesizing and processing polyurethane elastomers, which contributes to the complexity of their chemical structure as well as the significant variations in their physical conformation. These factors result in changes in the properties of polyurethane elastomers. Polyurethane elastomers are used in a solid state, and their mechanical strength under various external forces is the most important indicator of their performance. Generally speaking, like other polymers, the properties of polyurethane elastomers are closely related to factors such as molecular weight, intermolecular forces, segment toughness, crystallization tendency, branching and cross-linking, as well as the position, polarity, and size of substituents. However, unlike hydrocarbon-based polymers (such as PP and PE), polyurethane elastomers have a molecular structure composed of soft segments (oligomeric polyols) and hard segments (polyisocyanates, chain-extending cross-linking agents, etc.). Strong electrostatic forces exist between these macromolecules, especially between the hard segments, and numerous hydrogen bonds are often formed. These strong electrostatic forces not only affect the mechanical properties but also promote the aggregation of hard segments, leading to microphase separation and thereby improving the mechanical and temperature-performance characteristics of the elastomer. 1. The relationship between mechanical properties and structure: The mechanical properties of polyurethane elastomers depend on their tendency to crystallize, particularly that of the soft segments. However, polyurethane elastomers are used in an elastic state, and crystallization is not desired. Therefore, it is necessary to find a balance between elasticity and strength through formulation and process design, so that the resulting polyurethane elastomer does not crystallize at the operating temperature and maintains good elasticity; meanwhile, it should be able to crystallize rapidly when subjected to high stretching, with the melting temperature of this crystal being around room temperature. Once the external force is removed, this crystal melts quickly. Such a reversible crystalline structure is very beneficial for enhancing the mechanical strength of polyurethane elastomers. Whether polyurethane elastomers can exhibit reversible crystallization depends mainly on the polarity of the soft segments, molecular weight, intermolecular forces, and structural regularity. The molecular polarity and intermolecular forces of polyesters are greater than those of polyethers; therefore, the mechanical strength of polyester-based polyurethane elastomers is higher than that of polyether-based polyurethane elastomers ； The side groups in the soft segments reduce crystallinity, thereby lowering the mechanical properties of the product. The structure of the hard segments in polyurethanes also has a direct and indirect influence on the mechanical properties of polyurethane elastomers; generally, aromatic diisocyanates (such as MDI and TDI) have a greater impact than ester diisocyanates (such as HDI) ； Diisocyanates with a symmetrical structure (such as MDI) can endow polyurethane elastomers with higher hardness, tensile strength, and tear strength ； The effect of the structure of chain-extending crosslinking agents on the mechanical properties of elastomers is similar to that of diisocyanates. 2. The relationship between heat resistance and structure: The thermal stability of polymers can be measured by the softening temperature and the thermal decomposition temperature. Under normal circumstances, the thermal decomposition temperature of polyurethane elastomers is lower than their softening temperature. Generally speaking, polyester-based polyurethane elastomers have better heat resistance than polyether-based polyurethane elastomers ； For aromatic diisocyanates, the heat resistance order is PPDI > NDI > MDI > TDI. 3. Relationship between low-temperature properties and structure: The low-temperature elasticity of polymers is usually measured by the glass transition temperature and the cold resistance coefficient (or fragility temperature). Under normal circumstances, polyether-based polyurethane elastomers have better low-temperature flexibility than polyester-based ones. 4. Relationship between water resistance and structure: The effects of water on polyurethane elastomers: the plasticizing effect of water (water absorption) and the degradation effect of water. When the relative humidity is 100%, the water absorption rate of polyester-based polyurethane elastomers is approximately 1.1%, with a performance decline of around 10% ； The water absorption rate of polyether-based polyurethane elastomers is approximately 1.4%, with a performance decline of around 20% ； However, the hydrolytic stability of polyether-based polyurethane elastomers is greater than that of polyester-based polyurethane elastomers. 5. Relationship between structure and oil resistance and chemical resistance: Polyurethane elastomers exhibit good resistance to oils and non-polar solvents. Generally, polyester-based polyurethane elastomers have better oil resistance than polyether-based polyurethane elastomers ； The higher the hardness of the polyurethane elastomer, the better its resistance to oils and fats ； Polycaprolactone-based polyurethane elastomers have better resistance to chemicals such as sulfuric acid and nitric acid compared to other types of polyurethanes. Polyurethane elastomers generally have poor resistance to alkalis and highly polar solvents (such as **, turpentine, etc.).