The molecular weight of a polymer has a significant impact on its physical properties at different temperatures. Some of the key properties affected by molecular weight include mechanical strength, viscosity, glass transition temperature Tg , and melting temperature Tm .1. Mechanical strength: As the molecular weight of a polymer increases, the mechanical strength tensile strength, toughness, and elongation at break generally increases. This is because higher molecular weight polymers have longer chains, which leads to stronger entanglements and intermolecular interactions. These longer chains can also form more crystalline regions, which contribute to the overall strength of the material.2. Viscosity: The viscosity of a polymer solution or melt is directly related to its molecular weight. Higher molecular weight polymers have higher viscosities due to the increased chain entanglements and interactions. This can affect the processability of the polymer, as higher viscosity materials may require more energy and time to process.3. Glass transition temperature Tg : The glass transition temperature is the temperature at which a polymer transitions from a glassy, brittle state to a rubbery, more flexible state. The relationship between molecular weight and Tg is not as straightforward as with mechanical strength and viscosity. However, in general, as the molecular weight of a polymer increases, its Tg also increases, but only up to a certain point. This is because longer polymer chains have more chain entanglements and secondary bonding, which restricts the molecular motion and increases the energy required for the transition. Once the molecular weight reaches a high enough value, the Tg becomes relatively insensitive to further increases in molecular weight.4. Melting temperature Tm : The melting temperature is the temperature at which a polymer transitions from a solid, crystalline state to a liquid, amorphous state. The relationship between molecular weight and Tm is complex and depends on the specific polymer. In general, as the molecular weight increases, the degree of crystallinity and the melting temperature may increase due to the formation of more stable and ordered crystalline regions.In summary, the molecular weight of a polymer plays a crucial role in determining its physical properties at different temperatures. Higher molecular weight polymers generally exhibit increased mechanical strength, viscosity, and glass transition temperature. However, the relationship between molecular weight and melting temperature is more complex and depends on the specific polymer.