Lesson_3 Plastics and ceramics (6)

Lesson_3 Plastics and ceramics (6) - 16-3 Degree of...

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where M i is again the mean molecular weight of each size range, but x i is the fraction of the total number of chains within each range. Either M x or M n can be used to calculate the degree of polymerization. The two following examples illustrate these concepts. EXAMPLE 16-4 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. SOLUTION 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 an 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 ¼ 116 þ 146 ± 2 ð 18 Þ ¼ 226 g = mol Degree of polymerization ¼ 120 ; 000 226 ¼ 531 The degree of polymerization refers to the total number of repeat units in the chain. The chain contains 531 hexamethylene diamine and 531 adipic acid molecules. EXAMPLE 16-5 Number and Weight Average Molecular Weights We have a polyethylene sample containing 4000 chains with molecular weights
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  • Spring '14
  • Colombo
  • Physics, Polymer, Material Science, Plastics, Manufacturing, Metals, Molecular Weights

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