The molecular weight of a polymer has a significant impact on its physical properties, including viscosity and elasticity. As the molecular weight of a polymer increases, both its viscosity and elasticity generally increase as well. This is due to the increased number of atoms and bonds within the polymer chains, which leads to stronger intermolecular forces and entanglements between the chains.Viscosity:Viscosity is a measure of a fluid's resistance to flow. In the case of polymers, the viscosity of a polymer solution or melt is directly related to the molecular weight of the polymer. As the molecular weight increases, the polymer chains become longer and more entangled, leading to an increase in viscosity. This is because the longer chains have more points of contact with each other, which creates more resistance to flow when a force is applied.Experimental evidence:An experiment to demonstrate the effect of molecular weight on viscosity can be conducted by preparing polymer solutions with different molecular weights and measuring their viscosities using a viscometer. For example, solutions of polyethylene glycol PEG with varying molecular weights can be prepared by dissolving them in water at a constant concentration. The viscosity of each solution can then be measured using a capillary viscometer or a rotational viscometer. The results will show that the viscosity of the PEG solution increases with increasing molecular weight.Elasticity:Elasticity is the ability of a material to return to its original shape after being deformed. In polymers, elasticity is influenced by the molecular weight because longer polymer chains have more entanglements and stronger intermolecular forces, which contribute to the material's ability to resist deformation and return to its original shape.Experimental evidence:An experiment to demonstrate the effect of molecular weight on elasticity can be conducted by preparing polymer samples with different molecular weights and measuring their elastic properties using a tensile testing machine. For example, samples of polyvinyl alcohol PVA with varying molecular weights can be prepared by casting them into films. The tensile strength and elongation at break of each film can then be measured using a tensile testing machine. The results will show that the elasticity of the PVA films increases with increasing molecular weight, as evidenced by higher tensile strength and elongation at break values.In conclusion, the molecular weight of a polymer plays a crucial role in determining its physical properties, such as viscosity and elasticity. As the molecular weight increases, both viscosity and elasticity generally increase due to the increased number of atoms and bonds within the polymer chains, leading to stronger intermolecular forces and entanglements between the chains. Experimental evidence from viscosity and elasticity measurements supports this relationship.