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Oregon State University Ecampus Online Chemistry Lecture - Polymers

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Hi, I would like to talk a little bit about a magic trick. And, uh, magic trick is a little variation on the old ball and cups. In the old days, they would take a ball, cover it with a cup and play the old shuffle game. And then go, hey which cup is the ball under?? And maybe there was a slide of hands such as...that. But we are going to do a little variation because this is chemistry involving water. So I've got three empty party cups and I am going to pour water into one of them. And put some water into there. And the idea is I'm going to shuffle these cups and find out if you can keep track of which one I poured water in. There was no cutting of the film. And how many of you think it's in this one? Think it's in this one? Think it's in this one? Let try this one first. No, there's no water in this cup. Think it's in this one? No it's not in that one. Think it's in this one? No it's not that one. So what happened to the water? Where did it go? There is no water in these cups. There was no cutting of the film. It turns out that this had the water in it. Before I started the trick, I put a little bit of a powder in here and it's called super absorbent polymer. That's it's name, super absorbent polymer. And polymer is very much in line with a plastic. And this is the polymer, called super absorbent polymer that's used in diapers! Your disposable diapers! So when a baby goes ahead and urinates...it sucks all that absorbent stuff and holds it away from the baby's skin. So when I poured the water in here, super absorbent polymer absorbed a bunch of the water. And is sticky and holds onto it. Pretty neat. We'll talk about what polymers are right now. The word polymer, oh course is two words put together. "POLY" meaning many and "MER" actually meaning units. So, many units. Maybe you were bored when you were a kid, like in history class and you would take the little paperclips, hook them together, and make paperclip necklaces. Well, you were making a polymer. Many units. Not on the molecular level but with paperclips. What we're gonna do in chemistry over here to the right is...take some compounds. This one is compound A and this one is called compound B and we're not going to hook A to B We're going to hook A to B to another A to another B to another A to another B. We are going to link them back and forth. A B A B A B billions and trillions and trillions of times. The idea here is one of these molecules has two hands. A hand on this side, meaning something that will reach out and grab. And a hand on the other side. If you only have a molecule with one hand you can hold on to something and that's it. You can't go any further on this side. By having two hands you can link together. So one of these is going to have a B on the right and a B on the left. And one of these B molecules has got two hands and it's going to have A on the left and A on the right. And they are going to alternate back and forth. It turns out that this function group, as we call it, part of the molecule here that goes COOH is called a carboxylic acid group, COOH there, and it has the word "di" out in front because we've got ourselves two of them. This is a dialcohol. This doesn't have COOH it just simply has a OH attached to a carbon. There is no oxygen up there with the double bond. This is the alcohol group. So we call it a dialcohol. And the reaction happens when these two get together and water is eliminated. This carbon over here is going to form a new bond to that oxygen and that OH on this molecule and the H here are going to leave. You can clearly see that that's water, H2O. We call this a condensation reaction because condensation means the removal of a small molecule. Like when water comes out of the air and situates it's on a cold glass of iced tea. You would say condensation, so water leaves. So when these two react we are going to make A B A B A B... and it's going to make a long strand. Turns out that when we go ahead and make this we're going to make a long stand. And it's very similar to the material they like to use when making backpacks and disco slacks and all sorts of fabrics. So... make a polymer. We can make another polymer type. It's called a radical polymerization. Now a radical has a symbol big R with a single dot because a radical has an odd number of electrons. For a radical I give a nice example of this, and it's not OH minus, it is OH. Meaning that it doesn't have an extra electron and it has an odd number of electrons. Two here in the bond, total of seven. This is very reactive. What it's going to do is, it's going to come right out in front here. It's going to attack the carbon. It's going to take the electron out of this pie system and move it out in front and form a new bond. So this electron and electron here, will come over here and form two electrons in a bond. That's going to leave and electron here in this bond here to move out in front. And we have not solved the radical problem. We just have a bigger radical. We have this, we have this, and we still have an electron out front. Now, nobody in the polymer game is going to take one of these and react it with one of these. You are going to take this stuff, mix it up in a pot, you are going to use a little bit of this and a whole lot of this. It's called ethylene, it's common name, and when we put it in a pot we are going to use a lot of this. So what happens is one of these starts a chain reaction with this, this still is a radical, another one of these ethylene molecules will be attacked and another one, and another one, and another one until literally thousands, millions of these all line up in a row and you are going to make a long strand or a polymer. Now philosophically, questions can be asked like when does it end or another one of these radicals could come up or two chains could be building inside the pot and then...bam they hit each other and neutralize. We don't want a whole lot of chains going otherwise these will end up really short. So...an introduction to polymers. Polymers are plastics. Little water bottles, things like some disposal materials like a comb and a toothbrush. These actually came from a prison. I toured a prison with my son in cub scouts and they gave us these little items and of course they are polymers. Something really soft and flexible so that they couldn't be made, like, into weapons in a prison. Well, I hope you've enjoyed the little trick and introduction to polymer.

Video Details

Duration: 7 minutes and 32 seconds
Country: United States
Language: English
Genre: None
Views: 43
Posted by: umarket on Sep 24, 2009

Videos were taken from an Online Chemistry course provided by Ecampus at Oregon State University. The professor is Dr. Richard Nafshun.

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