Polydispersity and Molecular Weight Analysis

The video tutorial explains how to calculate the average molecular weight of a polymer using both number average and weight average methods. It also covers the calculation of polydispersity and the degree of polymerization, given the molecular weight of the repeat unit. The tutorial uses a simplified example with a molecular weight distribution to demonstrate these calculations, emphasizing the differences between number and weight averages and their implications for polymer properties.

What are the two types of averages calculated for polymer molecular weight distribution?

• Number average and volume average

• Volume average and density average

• Number average and weight average

• Weight average and density average

What is the molecular weight range for the first fraction in the example?

• 8 to 20 kilograms per mole

• 44 to 56 kilograms per mole

• 20 to 32 kilograms per mole

• 32 to 44 kilograms per mole

How is the number average molecular weight calculated?

• Sum of the density times the molecular weight

• Sum of the weight fraction times the molecular weight

• Sum of the fraction times the molecular weight of that fraction

• Sum of the molecular weight times the volume fraction

What is the weight average molecular weight in the example?

• 65.3 kilograms per mole

• 60.1 kilograms per mole

• 53.9 kilograms per mole

• 47.7 kilograms per mole

How is the weight fraction calculated?

• x_i times M_i divided by the total weight

• x_i divided by M_i times the average molecular weight

• x_i times M_i divided by the average molecular weight

• x_i divided by M_i times the total weight

What does a polydispersity index of 1.1 indicate?

• A very broad distribution

• A fairly narrow distribution

• A uniform distribution

• A random distribution

How is polydispersity calculated?

• Weight average molecular weight divided by number average molecular weight

• Weight average molecular weight times number average molecular weight

• Number average molecular weight divided by weight average molecular weight

• Number average molecular weight times weight average molecular weight

What is the degree of polymerization?

• The average molecular weight divided by the mass of the repeat unit

• The weight average molecular weight divided by the mass of the repeat unit

• The number average molecular weight divided by the mass of the repeat unit

• The total molecular weight divided by the mass of the repeat unit

What is the mass of the repeat unit in the example?

• 60 grams per mole

• 53 grams per mole

• 47 grams per mole

• 56 grams per mole

What does the degree of polymerization represent?

• The density of the polymer

• The total weight of the polymer

• The volume of the polymer

• The average number of repeat units in the polymer