ps3soln - Problem Set #3 BENG 434/ENAS 534 Biomaterials...

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BENG 434/ENAS 534 Biomaterials Due: Tuesday, October 21st at the beginning of class 1) You buy a 1920’s beach shack and the plumbing fails in a catastrophic way. Since you bought the shack, you have no money. You’re first plan is to make your own pipe for the plumbing. You look it up and figure out that you need PVC piping. (a) What does PVC stand for? Poly(vinyl chloride) the monomer is in parenthesis. Poly(vinyl chloride) is , technically, not the same as polyvinyl chloride (b) Show the steps in synthesizing PVC PVC goes by chain growth polymerization—free radical. (c) How is piping processed? (You may find it useful to read the following paper: pvcpipe.pdf on website) Plasticizers are typically added during or just post synthesis. PVC is most commonly made using a suspension polymerization technique, although bulk and emulsion can be used (for more detail see Odian, Principles of Polymerization , p. 308 on) Plasticizers are small molecules that make materials softer (less rigid) and more processable as well as often, less brittle—one doesn’t want one’s pipe to burst) Piping is most often extruded by heating up the PVC plus plasticizers and forcing the material through a die. One outcome of this is that the chains can take on orientation very nicely which can lead to anisotropic properties. (d) What are the major concerns that you need to think about in synthesis that will affect the processing and properties? Molecular weight is always an issue. You need to think about how to synthesize the material so that you have a reasonable mw but can still process it into the piping. You also need to be concerned about side reactions. In the presence of light and heat, PVC can break down and HCl can be formed. The addition of oxides and carbonates (a component of the suspension polymerization) help to reduce this breakdown. (Summarized from Odian again—see p. 309 on for details) 2) It turns out that you kind of stink at making and laying pipe. You decide that you need to make a great deal of money quickly but in an entirely legal manner. You saw the graduate, and you know money is in plastics. You decide to create the best, cheapest segmented polyurethanes around. (a) You have the following starting materials
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ps3soln - Problem Set #3 BENG 434/ENAS 534 Biomaterials...

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