The optimum ratio of diisocyanate and polyol required for the synthesis of polyurethane depends on the desired properties of the final product. In general, the stoichiometric ratio of diisocyanate to polyol is 1:1, meaning one isocyanate group reacts with one hydroxyl group. However, this ratio can be adjusted to achieve specific properties in the final polyurethane product.The ratio of diisocyanate to polyol affects the physical and chemical properties of the final polyurethane product in the following ways:1. Hardness and rigidity: Increasing the amount of diisocyanate relative to polyol will result in a harder and more rigid polyurethane material. This is because the diisocyanate forms a more cross-linked structure with the polyol, leading to a denser and more rigid network.2. Flexibility and elongation: Conversely, increasing the amount of polyol relative to diisocyanate will result in a more flexible and elastic polyurethane material. The higher polyol content leads to longer chains between cross-links, allowing for greater movement and flexibility.3. Tensile strength: The tensile strength of the polyurethane material can be influenced by the ratio of diisocyanate to polyol. A higher diisocyanate content can result in increased tensile strength due to the formation of a more cross-linked structure.4. Chemical resistance: The chemical resistance of the polyurethane material can be affected by the ratio of diisocyanate to polyol. A higher diisocyanate content can lead to increased chemical resistance due to the formation of a more cross-linked and dense network.5. Thermal stability: The thermal stability of the polyurethane material can be influenced by the ratio of diisocyanate to polyol. A higher diisocyanate content can result in increased thermal stability due to the formation of a more cross-linked structure.In conclusion, the optimum ratio of diisocyanate and polyol required for the synthesis of polyurethane depends on the desired properties of the final product. Adjusting the ratio can lead to changes in hardness, flexibility, tensile strength, chemical resistance, and thermal stability. It is essential to carefully control the ratio of diisocyanate to polyol to achieve the desired properties in the final polyurethane product.