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L20_Polymer_Properties_Annotated(2)

# 22 3850 c table 144b shows the22500 for the weight

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Unformatted text preview: weight-average molecular weight, as data 20,000–25,000 0.27 6075 taken from Figure 14.3b. The wi Mi products for the size intervals are tabu25,000–30,000 27,500 0.20 5500 lated in the 30,000–35,000 right-hand column. The sum of these products (Equation 14.5b) 32,500 0.08 2600 yields a value 35,000–40,000 of 23,200 g/mol for Mw. 37,500 0.02 750 Mn 21,150 Table 14.4b Data Used for Weight-Average Molecular Weight Computations in Example (b) To determine the degree of polymerization (Equation 14.6), it is first necProblem 14.1 essary to compute the repeat unit molecular weight. For PVC, each repeat Molecular Weight Mean Mi unit consists of two carbon atoms, three hydrogen atoms, and a single chloRange ( g/mol ) ( g/mol ) wi wiMi rine atom (Table 14.3). Furthermore, the atomic weights of C, H, and Cl are, 5,000–10,000 7,500 150 respectively, 12.01, 1.01, and 35.45 g/mol.0.02 for PVC Thus, 10,000–15,000 15,000–20,000 g/mol 2 m 2 1 12.01 20,000–25,000 62.50 25,000–30,000g/mol 30,000–35,000 and 35,000–40,000 12,500 17,500 3 1 1.01 g/mol 2 22,500 27,500 32,500 37,500 DP Mn m 0.10 0.18 35.45 g/mol 0.29 0.26 0.13 0.02 21,150 g/mol 62.50 g/mol Mw 338 1250 3150 6525 7150 4225 750 23,200 Lecture 20-21 Two Ways to Count Chains/Measure MW: Amount of Polymer ¯ Number-Average M General Trends of the Distribution: N Weight-Average ¯ Mw Since the weight-average puts a large emphasis on the higher molecular weight there is a: • Shift of the peak to the right and broadening of the distribution • Decrease in the peak height as compared to the number-average Molecular Weight → Polydispersity Index (PDI) ~ 2 -50 PDI play a role in injection molding! TP Lecture 20-21 So, How Does MW Affect Properties? Molecular Weight n, Polyethylene Tensile Strength Material State 58 86-226 254-1402 1402-9802 105 2 2 3-10 18-30 gas 3-8 8-50 50-350 >350 (MPa) liquid solid solid solid Why as the MW increases do we see the change? 1. Polymer chains become increas...
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