Hey guys, this is the last subtopic for stage 2 chemistry. This is subtopic 4.4 on materials. It's probably the biggest topic, so we'll be breaking this up into three major parts. The first major part is going to be on polymers.
I'll essentially be breaking up polymers into two videos. So to start off, we have these understandings. Polymers are produced from by additional condensation reactions.
You need to be able to identify whether a molecule could undergo polymerization given its structural formula and if so the type of polymerization. Also identify a polymer as being the product of an addition polymerization or condensation polymerization given its structural formula and identify the repeating unit of a polymer given its structural formula. From previous studies we've learned that polymers are long chain molecules consisting of repeating units and polymers can be made from these so-called building blocks which we call monomers.
You'll see these two terms being used, but it's important to understand that these two aren't able to be used interchangeably. So in other words, repeating units are not the same thing as monomers. There are two types of polymers.
We can say that there are addition as well as condensation polymers. On this slide here we can see some carbohydrates. So at the top we have a glucose molecule which is classified as monosaccharide. and we have amylose starch here which is classified as a polysaccharide or a polymer of glucose.
From our polymer structure here we can actually represent the repeating unit as shown by these square brackets and if we just sum up all the atoms within these square brackets here we would find it has the formula of C6H10O5. This is put in brackets and then an N as a subscript to indicate that this repeats a number of times. If we then go to the monomer used to make this up which is glucose and we count the atoms we find that the monomer has a molecular formula of C6H12O6 there is a clear difference in the formulas for both the monomer and the repeating unit one showing it repeats and number of times and one is an individual or discrete unit during our studies we've seen how previous concepts from stage one as well as stage two have come back. So in this case we're going to be talking about addition polymers and this does come back to stage one chemistry subtopic 3.4 on polymers. Addition polymers can be formed from addition reactions.
In order to form addition polymers we need alkene functional groups or carbon to carbon double bonds. The monomers must contain at least one carbon to carbon double bond and in the examples we'll have a look at they typically will. Another key point is that with addition polymerization we'll see no loss of atoms as these monomer units join to one another. But what we'll see is this carbon to carbon double bond essentially being converted into a single bond which then frees up a bond with the carbon atoms to then join onto a successive monomers structure. We have a general formula here where we've got a carbon to carbon double bond and they have variable groups here labelled as AB, X and Y and it really doesn't matter what these groups are but through an addition reaction with the right conditions we can get the joining of these monomer units to form a structure which looks like this.
So now we can see that each carbon atom is bonded together through a single carbon to carbon bond we still have those variable Groups A, B, X and Y. We can indicate the repeating unit by using the square brackets and we've just got a subscript in here to indicate that this occurs a number of times. And another important thing would just be to note the difference between the repeating unit and the monomer. So the monomer has a carbon to carbon double bond whereas the repeating unit does not. One is a discrete molecule whereas the other one is a repeating structure.
On this slide we're going to consider some different examples. So at the top here we have ethene and we can undergo polymerization reactions to form a polymer of ethene known as polyethene or polyethylene. Again, given the right conditions that could include things such as catalysts or the addition of energy or temperature or pressure, we can get one of the bonds within the double bond essentially breaking and then a successive ethene molecule adding across that double bond and joining on to this ethene molecule itself.
So when that happens we get a structure that looks like this. It's important to note that continuous chain of carbon atoms going along because this is what we can use to help identify addition polymers which will be different to condensation polymers. Common use for polyethene is in the construction of our typical plastic bags but there are other examples of polymers that can be used.
For the second example we have here vinyl chloride. which consists of a carbon to carbon double bond as well but we have one chloride group or chlorine atom bonded to one of the carbons so in this addition polymerization we're going to get the breaking of one of the bonds within the double bond and then we get the joining together or adding across of another monomer unit which itself will also undergo the same process and this will occur in a bit of a chain reaction we end up producing a molecule that looks like this Also note that these bonds here are just drawn without any atoms and this just indicates that this structure continues on. We can see the repeating unit here which consists of two carbon atoms like with the previous example of polyethene. So we can see this section here we should be able to essentially copy and paste it over and over again to allow us to determine the structure of it.
and the polymer is commonly referred to as PVC which stands for polyvinyl chloride which we typically use in piping and plumbing. Condensation polymers on the other hand is something that we covered previously in stage 2 chemistry topic 3. It makes sense that they're formed from condensation reactions. Condensation reactions result in the release of a small molecule which is typically water. We can typically classify condensation polymers as either polyesters or polyamides.
So polyesters consist of ester functional groups, polyamides with amide functional groups, and they can be formed in one of two ways. That's either with one monomer or with two monomers. If we look at polyesters, then they could be formed from one monomer, which would be called a hydroxycarboxylic acid. If there are two monomers, then we would have a diol as well as a dicarboxylic acid. We can do the same thing for polyamides if there's only one monomer.
that would be termed an amino carboxylic acid. If there's two monomers we would have a diamine and a dicarboxylic acid. If you've watched my previous videos on subtopic 3.7 esters then you would have seen these slides previously so we're just going to go through it quickly again. So the first method which involves one polymer is a hydroxycarboxylic acid.
We can see a range of general formulas of hydroxycarboxylic acids so they would have some type of variable group here in the middle with a various number of carbons. These monomer units are going to undergo condensation reactions, so we have a carboxyl group and a hydroxyl group which are going to be involved in the elimination of water as a small molecule. We can see over this side as well. And when these atoms are removed as water, that then frees up a bond for this carbon as well as this oxygen.
So it allows for these two atoms to form a new covalent bond, and in doing so we end up forming our polyester. From this structure hopefully you'd be able to see that the repeating unit consists of this component here so this variable number of carbons in a hydrocarbon chain followed by our ester group and here in red we can just see circled are the ester groups in our polymer chain. The second method involves two monomers that is a diol and a dicarboxylic acid so we're just going to see a range of those lined up here now in different colors so we've got a dicarboxylic acid here and then diol. We're going to get the association of our carboxyl group and our hydroxyl group here. We get the elimination of water as a small molecule.
We then free up bonds between these atoms and they're going to join together to form our various ester functional groups. We can see in square brackets this is our repeating unit so it somewhat appears bigger but that would just depend on how big these R groups are. And finally again we can see circled are the ester groups.
Like with subtopic 3.7 on esters, if you've watched subtopic 3.8 on amides, then you would have actually seen these slides already. So in terms of polyamides, we can have them produced from one monomer being an amino carboxylic acid. And very quickly, we can see the alignment of these amino carboxylic acids. Instead of a hydroxyl group, we've got an amino group now that's going to associate with our carboxyl group.
We are going to get the elimination of water and then we're going to get the formation of... amide functional groups. Those amide functional groups can be seen in red here and we can see the repeating unit in the square brackets there.
For the case where there's two monomers we have diamines and dicarboxylic acids. We can see an alignment of these molecules here. We're going to also get condensation reactions which release water.
We then get the joining together of these monomer units to produce our polyamide. To finish up we're just going to consider some examples of condensation polymers. So starting with the polyester we have polyethylene terephthalate or PET for short or PET. We can see the two monomers that are used to produce this and they will undergo condensation reactions to produce a polymer with this repeating unit. We can see that PET is made from two different monomers so we've got a dicarboxylic acid here and its name is benzene 1,4-dioic acid and then we've got a diol here which is ethane 1,2-dioil.
We can most commonly associate PET as being polymer which we use to manufacture plastic bottles. In regards to polyamides we have here Nylon 6-6. So here are our two monomers that can go to produce our polymer with this repeating unit. Our first monomer we should be able to see that it is a diamine and it consists of six carbon atoms.
So this is called 1,6-hexane diamine and over here we can see that we have a dicarboxylic acid. Also with six carbon atoms, so it is called hexane dioic acid. Nylon 6-6 as well as other variations of nylon can be used to make quite a large range of products. We can see some examples over to this side.
Other examples could be things like the bristles within toothbrushes, parachutes and also stockings. This includes part one of the polymer section of subtopic 4.4 on materials. I'll see you guys in the next video.