problems_section_5[1]

# problems_section_5[1] - Problems – Section 5 Polymers 1...

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Problems – Section 5: Polymers 1. One can typically strengthen a thermoplastic polymer by (check all that apply): __ decreasing M w __ increasing the degree of branching __ adding bulky sidegroups __ increasing the ratio of crystalline to amorphous polymer __ adding polar side groups 2. Consider two different solid poly(styrene) solids at room temperature. One has an average degree of polymerization (DP) of 30. The other has an average DP of 1000. If identically shaped specimens of each polymer are loaded in tension, would you expect the maximum load that each could sustain to be the same or different? Briefly justify your answer. 3. The boiling temperatures of methane (CH 4 ), carbon tetrachloride (CCl 4 ), and water (H 2 O) are 111 K, 350 K, and 373 K, respectively. For each of these three molecules: a) make a 2-d sketch the structure of the molecule; b) calculate the percent ionicity of the C-H; C-Cl, and O-H bonds c) develop a brief argument justifying the magnitudes and general order of boiling temperatures for these three molecules. 4. Teflon ™ is a tradename for poly(tetrafluroethylene) [PTFE], and it is often used in non-stick coating applications (e.g. frying pans). Develop an argument based on their permanent dipole structure to rationalize why the interaction between Teflon and water would be different from that between polyethylene and water. 5. Methane (CH 4 ) has a lower boiling temperature than water (H 2 O). Briefly explain why this is true in terms of the bonding between molecules in each of these two substances. 6. Gore-Tex TM is made from by stretching poly(tetra flouroethylene)[PTFE; also known as Teflon] to plastic elongations of several hundred percent. Briefly explain why fibers of Goretex say 200 mm in diameter are extremely strong when loaded in tension. Hint – Consider how polymer molecules orient when stretched and how this affects what type of bonding supports the tensile load.

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7. Suppose you are trying to select a material for use as the hood of a car. List the important properties required by this application and briefly indicate why a polymeric material would or would not be good for it. 8. From the following list, check all the valid reasons for using a polymer in place of an aluminum alloy. The polymer has: __ better formability; __ lower density; __ higher modulus; __ higher melting temperature. Briefly justify your reasoning.
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