Polyacrylamide (PAM) is a polymer composed of repeating units of acrylamide. It is available in various grades distinguished by their molecular weights. The molecular weight of PAM affects its physical properties and performance in different applications. Here are the key differences between polyacrylamide with different molecular weights:

1. Molecular Weight: PAM can have molecular weights ranging from several thousand to millions of Molecular weight. The higher the molecular weight, the larger the polymer chains and the increased viscosity of the solution.

2. Solution Viscosity: Higher molecular weight PAM forms more viscous solutions. This property is important for applications like thickening, flocculation, and solid-liquid separation processes.

3. Flocculation Ability: PAM with higher molecular weights exhibits stronger flocculation ability, which is useful in water treatment processes where suspended particles need to be agglomerated and settled.

4. Shear Resistance: Higher molecular weight PAMs offer resistance to mechanical shear forces, making them suitable for applications in high-shear conditions such as oil drilling or hydraulic fracturing.

5. Gel Formation: Higher molecular weight PAMs have a higher tendency to form gels, making them suitable for gel electrophoresis and other gel-based applications.

6. Dissolution Time: Lower molecular weight PAMs typically dissolve more quickly than higher molecular weight ones due to their smaller particle size.

7. Price: The cost of PAM increases with increasing molecular weight, as higher molecular weights require more complex synthesis processes.

When selecting a grade of PAM, it's essential to consider the specific requirements of the application, such as desired viscosity, flocculation efficiency, shear resistance, and, to choose the most appropriate molecular weight grade.