So, today, we're going to be talking about polymers. Polymers are basically long chain molecules, and they're made up of many repeat units called a mer. Right, poly meaning many and mer meaning a unit, all right? And they were the first engineered materials that started from basically simple chemicals, like ethylene and propylene.

Traditionally, a polymer is a pure material, and a plastic is considered a composite. So what are the properties that we normally associate with a plastic, right? Well, obviously, compared to something like steel or copper and bronze, it is a softer material, so it has lower strength. It has lower temperature stability, so that it will melt at relatively low temperatures, or it will degrade at low temperatures.

All right? It typically is waterproof. It's less reactive to certain environments than metals, for example it doesn't corrode like a metal does typically. It has a very long elongation that can happen, so if you have a rubber band, for example, it can stretch and that generates a tremendous elongation, right, relative to, say, a piece of steel.

I can't stretch it that far before it breaks. And, in general, they're lighter. They have a lower density. So you use them in situations where you don't want to have something heavy. All right? And they're also much easier to process. So, it's impossible to injection mold, for example, plastics into complex shapes, whereas a metal, you might have to machine it.

All right? So what were the first polymers? Well if we go back in time, and you look, the very first polymers were the natural occurring polymers like Bitumen, which we talked about before, which is basically tar. Or silk was a polymer, right? It's a form of cellulose. And then you have rubber, right rubber was discovered in the it's basically a coagulate of sap that comes from the Hebe tree.

Right, this is a piece of raw rubber. And the Caribbean it was actually used to wear, people would wear it on their feet and what not and so it was used a lot. They made balls out of it. They would kick it around, have fun with it. The problem was is that it's actually very, very sticky.

So in the 1700s it was brought back to France and in 1820 Mcintosh started missing this rubber with Napta which is basically gasoline to make raincoats. And they were obviously very sticky and they were also very brittle. So they had a lot of problems with their raincoats. And that was actually solved by another gentleman named Goodyear.

And we're gonna talk about what he did to make that work in a second. But first, to understand how he solved that problem, you have to understand more about a polymer. So a polymer is basically a material that starts from something relatively simple. Like if you take an ethylene molecule that's just a carbon that's double-bonded to another carbon.

Just two carbons. The four hydrogens hanging off of it. Then, if I open up that double-bond and actually allows it to chain up or to hook up to the next ethylene. And the next ethylene. And so by doing that process, I can make polyethylene. I can stick these chains of carbon together.

And they can become quite long. I can do the same thing with propylene. And then what would happen is I would wind up with this carbon, carbon, carbon chain and then I'll have this little methyl group hanging off the bottom. All right? And that's what we call polypropylene.

So when you hook these chains together, we say you've polymerized the molecule, right? Now, there's lots of side groups that you can put on that chain. Right, we just put a little methyl group and polypropylene hanging off, but what would happen if I pull that off and I stuck a chlorine in there?

Well, then I would have poly vinyl chloride, or what you know as PVC. Right, I could take that off, and I could stick a benzine ring in there, which is like six little carbons stuck together. If I do that, now I have polystyrene, or what you know as styrofoam, all right.

Or I could rip off all the hydrogens, and replace them with just fluorines, and now I have polytetraflouride, which is what you know as teflon. So how I play with those side chains had a lot to do with the properties and the different flexibility in materials that I could make.

So now back to the challenge of rubber. I start with this really sticky stuff and I wind up making something that's very useful. How did we do that? All right so Charles Goodyear, in the 1830s, was a owner of a hardware store and he loved to invent stuff.

And so he was sitting around trying to figure out how he could and improve rubber. And so, what he did was, he finally decided on adding sulfur. He wasn't quite sure what he was doing but what he found out was that when he added sulfur, what he was basically doing was cross-linking the chains.

So if I have all these long chains of carbon, the sulfur actually bridged one chain to the next. And by doing that, it made that material have this tremendous elastic strength, all right? And it also kept it from being sticky. And so by cross-linking it in a process that he called vulcanization, he improved the material tremendously.

Charles Goodyear is so excited about this invention that he sent material over to Macintosh and said, let's collaborate and figure out what in the world is making this material improve by the use of sulphur, and how is this working? And Macintosh basically took the samples, decomposed them, figured out there were sulphur in them.

And then reproduce exactly what Goodyear had done. And so, then he filed a patent two months before Goodyear filed a patent. And so, he wound up basically grabbing the market from Goodyear. Now, Goodyear did not die a pauper. He still did okay. So, it quickly became evident, that now that I had a stable form of rubber, the first, and best, application for that actually was in car tires, and so a lot of people started using this for transportation, and governments realized this was critical for moving larger pieces of equipment during wars.

And so the supply issues in World War I and World War II became critical because all of the rubber was coming from these trees that were down in the tropics, and so Germany quickly realized that they were not going to have access to this, and the American's actually in, World War two, lost access to them in the South Pacific when the Japanese took over all those islands, and so they decided to go ahead and synthesize rubber in the laboratory.

And so by the end of World War II, there was a very large quantity of the rubber that was being used, was being used from a synthetic source, not from the natural occurring tree. So the next polymer that we're interested in is a polymer called cellulose nitrate. This material was discovered by Schonbein at the University of Basel, in 1846.

And what he did was he found that if he took paper, and he dissolved in nitric and sulfuric acid, that he could extract a polymer from this. In 1868, Phelan and Collender launched a challenge. They offered a $10,000 prize to anyone who could replace the billiard ball, which was at that time made of ivory, with a synthetic material.

All right? And so in the time when cellulose nitrate was discovered, Parks had figured out that you could soften this material using camphor. And so Hyatt came along and decided he would use cellulose nitrate to make billiard balls. And it was a great invention. It worked very well.

Cellulose nitrate worked fine. It had one problem. When you make cellulose nitrate, all right what you do in effect is you take the hydroxyl group on this cellulose, and you replace it with an NO3 group from the nitric acid. Well, and NO3 group has lots of oxygens, and that tended to make the material very flammable, even explosive, and so, if you're making, if turns out if you're making a billiard ball, and you touch that billiard ball with a cigar, it will actually explode, or if you actually hit another billiard ball into it, it will actually cause a minor explosion to happen just from the connection.

So it turned out that there are a whole bunch of bars that every time that they said that they broke the pool balls apart that everybody pulled out their gun cuz they thought there was a gun fight going on cuz the billiard balls were popping. So that was not the greatest invention.

In 1890, another person named Chardonnet replaced the nitrates on this cellulose nitric with xanthates. And in doing so, he invented the first synthetic fiber, which he called Rayon. And it wasn't until about the 1930s that we actually discovered the first synthetic polymers that were not based on natural products.

Remember up till now we've been using wood as our starter or the rubber from a rubber tree as a starter and the 1930s Fawcett and Gibson came along and they accidentally polymerized polyethylene. Polyethylene was an important material because it actually is extremely good for use in radar cabling and so during World War II it was used, and it was actually kept as a secret from anybody, so they didn't know about it.

Now the biggest problem with polyethylene is, in addition to being very difficult to synthesize, was that it had a tendency to side branch. So if you're trying to chain these carbons together like I've been talking about, what would happen if suddenly at one point the carbon just goes off in another direction and the rest of the chain keeps growing, you have what's called side branching.

If you gets lots of side branching, then the polymer when it forms doesn't have the same property as another one that had less side branching. So you're properties were very variable all right, and they wound up with generating piles and piles of polyethylene that were basically unused because they couldn't sell it because the properties were all over the place.

So they couldn't figure out what to do with this material. And along comes this invention that basically saves the polyethylene industry. And the invention was the hula hoop. So the hula hoop it turns out, you could make with all kinds of different molecular lengths of polyethylene. And it didn't really matter.

Nobody cared about the properties of the hula hoop. Only that it worked, right? And so that allowed them to use up vast quantities of this stored polyethylene they had. And at the same time, a gentleman named Ziegler and another one named Natta came along and they invented catalysts in the early 50s.

And these catalysts allowed you to polymerize polyethylene. Very long chains, Ziegler catalysts would do this, and without any side branching. So you got very controlled properties in your polyethylene. Natta did the same thing with polypropylene, and they won the Nobel Prize in Chemistry for the invention of this Ziegler Natta Catalyst family.

So, what you’re going to hear more about in your chapter reading is tupperware. Tupperware is made from polyethylene or polypropylene. All right, and it's a really important invention because Earl Topper figured out a way to use polyethylene, but what you're gonna learn about is the fact that he could not sell it, and that fell on Brownie Wise to figure out how to do that.

So you're gonna learn all about that in your reading. Now, low-density polyethylene is what you see a lot of in, for example, plastic bags. They're relatively short chained molecules. If you make it very short it becomes something like floor wax. All right? But it's used a lot today in other applications like containers, etc.

And you can change the properties of polyethylene by changing the density. So you can go from low-density polyethylene, which has a market-share that's something in the order of $22 billion in 2009 to high-density polyethylene. High-density polyethylene is a material that has very long chains that will crystallize and pack into a nice routine order, and because of that, it becomes very, very strong.

So high density polyethylene is used for example in a lot of your tupperware today and it also has a very large market share. And so now, another way that you can do one of these basic materials, as I talked to before, is polypropylene. Polypropylene, because they have these methyl groups that are sticking on the side, it depends upon which side you put them on.

Because of thanks to Natta's, Natta's catalyst, you can now put them all on the same side. We call that isotactic material, and that allowed it to crystallize. And because it has this intermediate level of crystallinity, it has properties that are something between low density and high density polyethylene.

And so it's very normally a very tough and flexible material, and polypropylene is used in a lot of fabrics and things like that. Now, let's talk about other forms of polymers. So, DuPont, in the 1930s, there was a scientist there named Plunkett, and he was trying to discover a way to make a lubricant, and he was using polytetraflouroethylene inside of a canister, and one day he turned it on.

He knew the canister was full. Nothing came out. So he was trying to figure out how to use this tetrafluoroethylene, and because nothing came out he sawed off the top of the canister and he looked inside. Turned out there was this white powder. So he did a bunch of experiments on it.

He tried to dissolve it. Turned out it was very slippery, he couldn't dissolve it. He had accidentally discovered teflon. It was kept a secret until after the war because it was used a lot in the war effort of World War II. At the same time, there was another gentleman named Carothers at DuPont.

Carothers came up with a very clever idea. He decided to react this, a series of carbon chains, say six carbons, with a hydroxyl group and a double bonded O on it, so this is what we call a carboxylic acid with a diamene. Something that a bunch of carbons and then an NH group on the end, NH2.

And by doing that he could actually rip off a hydrogen from the NH and the OH from the carboxylic acid. And make water, and the chain would actually stitch itself together, and what he discovered was nylon. And so nylon is an incredibly versatile polymer, because it has some properties like it's very chemically resistant, and has a relatively high melting point.

And it's used in a lot of applications, everything from nylons that were basically hosiery early on to string fishing line to other materials. Okay, so we're talking about nylon. Nylon is actually made from two different chemicals. One of them is called hexamethylenediamine. Boy that's a big word. Hexamethylenediamine, it means that you got hexamethyles, six methyl groups.

And then you've got two amine groups on the end. These are these N-H groups that you saw in the chemical formula for nylon. So what I'm gonna do is I'm taking a little of the hexamethylenediamine and I dissolved it in water. So now I'm gonna pour that into a beaker.

When I do that, all right, there it is just looks like a clear liquid solution water. And now the second chemical that you use when you make nylon is some sort of in this case I'm using chloride. It's basically ten carbons all chained together, but then I have a C double bond O carboxyl group and a chlorine so what's gonna happen is that when I pour this in, on the surface it's gonna actually be lighter cuz it's dissolved in heptane.

And so when I dissolve this thing, here I'll pour it on here. What you're gonna see is that Now this material is sitting now on top. And what happens is what we call an interfacial polymerization. Again, big word. What it means is that I have, at the interface I'm forming nylon.

So if I reach down through that interface, and I pull out. I can actually pull out a strand of nylon. Right, that is forming at that interface. So this is the long chain polymer that's been synthesized but from these two chemicals, right? And this is actually one of the methods that you can use to make a polymer.

Now, obviously, commercially, you're not gonna sit there and try to pull out strands of nylon. But it's a very nice way of showing you how polymerization can occur at an interface. All right? So you don't have to just do it at the interface, you can actually just stir it up.

And if you do that, then it will start to react completely, and you can see what's gonna happen here. I pull out a whole glob now of nylon that's formed. So, if you are making a batch of this stuff in a factory, then you would obviously react it to make larger quantities up like this.

And then you'll actually extrude it later on to make the strands, for example, in fishing line. So a byproduct of this reaction is actually hydrochloric acid. So that's because I used a chloride. Normally, when I do this reaction the byproduct will be water. And so it's a condensation polymerization because it condenses water out.

But water reacts at higher temperatures so because I wanted to react this at room temperature I used a chloride. Because it reacts at lower temperatures. So Carothers was a very interesting man. He was a Professor of Organic Chemistry at the University of Illinois. At Harvard, before he became the Director of R & D at DuPont, and he was Director from 1928 to 1937.

And he developed in that time frame nylon as well as neoprene which is an artificial rubber. He launched over 50 patents. He was extremely intelligent and a brilliant man but he suffered from chronic depression and unfortunately he killed himself at the age of 41. So polymers basically come in two simple forms.

If we think about you it, you have thermoplastics and thermosets. A thermoplastics is a polymer that can melted down again and recycled. So your two liter bottles, right, is a polyester that is a thermoplastics material and it can be recycled. Thermosets are materials that have been cross linked.

And because of that, they typically cannot be melted down anymore. So thermostats are materials that the only way you can recycle them for example, a car tire is to grind it up and then use it as a composite material in another system. Now, polymers you have really interesting properties when you're talking about thermoplastic materials.

For example, if I take this piece of polyethylene all right, the polymer itself is not aligned. These chains are all randomly oriented inside this polymer. So, if I take this polymer and I start to stretch it what's gonna happen is those chains are gonna start to line up.

And you can see this thing is starting to line up, so in that center region right here it is lining up. And as I continue to pull on it, these chains are slowly lining up. Now at some point all the chains become lined up, and so there's certain properties of a material.

And so if I line up all the chains then at this point, the property of this material becomes much, much stronger, all right, and so that is a property of a polymer that you can actually utilize. So, if you're making string fishing line, for example, you'll actually pull on that polymer to the point where all the chains line up, and then it develops a very high tensile strength.

If you actually now line up those chains and have something in the backbone that will actually stitch those chains together a little bit, then you can create a material, for example, that was the principle behind Kevlar. All right? Which has very, very high tensile strength. So we talked about a lot of different polymers.

And polymers have only been around for a couple of hundred years. Yet, in that time frame, they have grown to the point where by weight, their, the amount of polymers that we used are comparable to many of the metals that we use. So it's one of the most commonly used materials in the world.

A tremendous number of applications. One of the interesting things when you look at it is, the applications for polymers. An awful lot of it is used in packaging, right? And so, that's where it becomes a challenge for us to figure out how to recycle this material. Because if you put a polymer into a landfill, it will not decompose for hundreds of years.

And so, it's a non-renewable resource. All right? But it is recyclable, so the plastics challenge is to figure out how you can recycle polymers such that you actually decrease the impact of the production of this material on the environment. All right? So when we think about the age of plastics, one of the things that you have to think about is sustainability.

So if you look at how materials have changed since we first started using them. When we first started using materials, the amount that came from renewable resources was nearly 100%. And now almost 100% of the materials that we use comes from non-renewable resources. And so, this is one of the big challenges for polymers is how do you actually develop polymers that come from renewable resources.

So, when you watch your video you're gonna actually see how we've developed new biological sources of polymers that may enable us to create future plastics from a renewable resource and stop using oil from the ground for this application.