Chap 15 Solns
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CHAPTER 14 POLYMER STRUCTURES PROBLEM SOLUTIONS Hydrocarbon Molecules Polymer Molecules The Chemistry of Polymer Molecules 14.1 On the basis of the structures presented in this chapter, sketch repeat unit structures for the following polymers: (a) polychlorotrifluoroethylene, and (b) poly(vinyl alcohol). Solution The repeat unit structures called for are sketched below. (a) Polychlorotrifluoroethylene (b) Poly(vinyl alcohol) Molecular Weight 14.2 Compute repeat unit molecular weights for the following: (a) poly(vinyl chloride), (b) poly(ethylene terephthalate), (c) polycarbonate, and (d) polydimethylsiloxane. Solution (a) For poly(vinyl chloride), each repeat unit consists of two carbons, three hydrogens, and one chlorine (Table 14.3). If AC, AH and ACl represent the atomic weights of carbon, hydrogen, and chlorine, respectively, then m = 2(AC) + 3(AH) + (ACl) = (2)(12.01 g/mol) + (3)(1.008 g/mol) + 35.45 g/mol = 62.49 g/mol (b) For poly(ethylene terephthalate), from Table 14.3, each repeat unit has ten carbons, eight hydrogens, and four oxygens. Thus, m = 10(AC) + 8(AH) + 4(AO) = (10)(12.01 g/mol) + (8)(1.008 g/mol) + (4)(16.00 g/mol) = 192.16 g/mol (c) For polycarbonate, from Table 14.3, each repeat unit has sixteen carbons, fourteen hydrogens, and three oxygens. Thus, m = 16(AC) + 14(AH) + 3(AO) = (16)(12.01 g/mol) + (14)(1.008 g/mol) + (3)(16.00 g/mol) = 254.27 g/mol (d) For polydimethylsiloxane, from Table 14.5, each repeat unit has two carbons, six hydrogens, one silicon and one oxygen. Thus, m = 2(AC) + 6(AH) + (ASi) + (AO) = (2)(12.01 g/mol) + (6)(1.008 g/mol) + (28.09 g/mol) + (16.00 g/mol) = 74.16 g/mol 14.3 The number-average molecular weight of a polypropylene is 1,000,000 g/mol. Compute the degree of polymerization. Solution We are asked to compute the degree of polymerization for polypropylene, given that the number-average molecular weight is 1,000,000 g/mol. The repeat unit molecular weight of polypropylene is just m = 3(AC) + 6(AH) = (3)(12.01 g/mol) + (6)(1.008 g/mol) = 42.08 g/mol Now it is possible to compute the degree of polymerization using Equation 14.6 as 14.4 (a) Compute the repeat unit molecular weight of polystyrene. (b) Compute the number-average molecular weight for a polystyrene for which the degree of polymerization is 25,000. Solution (a) The repeat unit molecular weight of polystyrene is called for in this portion of the problem. For polystyrene, from Table 14.3, each repeat unit has eight carbons and eight hydrogens. Thus, m = 8(AC) + 8(AH) = (8)(12.01 g/mol) + (8)(1.008 g/mol) = 104.14 g/mol (b) We are now asked to compute the number-average molecular weight. Since the degree of polymerization is 25,000, using Equation 14.6 14.5 Below, molecular weight data for a polypropylene material are tabulated. Compute (a) the number-average molecular weight, (b) the weight-average molecular weight, and (c) the degree of polymerization.
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