In addition to chemical structure, the molecular weight of polymers also influen

ID: 512164 • Letter: I

Question

In addition to chemical structure, the molecular weight of polymers also influences their bulk properties. Consider the following two reactions:

Case B) 25 mg of azobisisobutyronitrile (AIBN) and 65.3 g of methyl methacrylate

In the theoretical* case of all resulting polymers within this sample having the same molecular weight, what would be:

(i) the molecular weight of a single polymer (in amu)

(ii) the number of repeat units in each polymer, and

(iii) the total mass of all polymers yielded from the polymerization?

For the reaction:

i) AIBN + MMA ------ PMMA

there are 65.3 g of the monomer, methyl methacrylate (MMA)

Molar mass of MMA = 100 g/mol

# moles of monomer MMA = 65.3/100 = 0.653 moles

Theoretically, we should expect 0.653 moles of the product i.e the polymer PMMA

Now, the mass of polymer formed = moles of polymer formed * mol wt of a single monomer unit

= 0.653 * 100 = 65.3 g

This gives a molecular weight of the polymer as 100 g/mol

ii) Number of repeat units = mol wt of polymer/mol wt of each repeat unit = 65.3/65.3 = 1

iii) Total mass of Polymer PMMA = moles * mol wt = 0.635 * 100 = 63.5 g

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