Homework 10

# Homework 10 - MSE 230 HW10(due 04/08 04/09 Spring 2010 This...

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MSE 230 HW10 (due 04/08, 04/09) Spring 2010 This assignment covers polymers and composites over two weeks. It is due in recitation the week after the exam, so that you do not have a homework assignment due the week of the exam. 1. In order to get an idea of the size and number of “macromolecules” that constitute polymers: (a) Calculate the length of individual polyethylene molecules having molecular weight of 10,000, 100,000 and 1,000,000 g/mol if the molecules were straightened as in Fig. 14.5(b) so the carbon atoms all lie in a plane (i.e., straight end-to-end length not including the zigzagging). The carbon-carbon bond length is 0.155 nm and the tetrahedral bond angle is 109°. (b) Polyethylene has a density of ~1 g/cm 3 . Calculate the number of molecules in 1 cm 3 of polyethylene having the three molecular weights in part (a). 2. The table shows the molecular weight data measured for a particular polytertrafluoroethylene (Teflon). (a) Plot histograms for the molecular weight distribution on a number basis (Number fraction of molecules) and on a weight basis (Weight fraction of molecules). (b) Calculate the number-average molecular weight and the weight-average molecular weight. (c) If the price of the polymer were proportional to its “molecular weight,” which of these averages would be better to use if you were the buyer versus the seller. Explain.

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