Degree of Polymerization for 6,6-Nylon
Calculate the degree of polymerization if 6,6-nylon has a molecular weight of 120,000 g/mol.
The reaction by which 6,6-nylon is produced was described in Example 16-3. Hexamethylene diamine and adipic acid combine and release a molecule of water. When a long chain forms, there is, on average, one water molecule released for each reacting molecule. The molecular weights are 116 g/mol for hexamethylene diamine, 146 g/mol for adipic acid, and 18 g/mol for water. The repeat unit for 6,6-nylon is
The molecular weight of the repeat unit is the sum of the molecular weights of the two monomers, minus that of the two water molecules that are evolved:
M_{repeat \ unit} = 116 + 146 – 2(18) = 226 g/mol
Degree of polymerization = \frac{120,000 \ g/mol}{226 \ g/mol} = 531
The degree of polymerization refers to the total number of repeat units in the chain.