 Last one you write down is thermosetting polymers, the fourth type, thermosetting polymers. Write down these are semi-fluid substance, these are semi-fluid substance with low molecular weight, which when heated, which when heated undergo a change in chemical composition. Okay, semi-fluid substance with low molecular weight, which when heated undergo a change in chemical composition to give a hard and insoluble mass, hard and insoluble mass, insoluble mass. The hardness is because of extensive cross-linking, is because of extensive cross-linking. Okay, so cross-linking is again that's the same thing, we have a bond between the two layer. Okay, so when you heat this chemical change takes place and cross-linking occurs and hence it becomes hard. Okay, so these are the four different types of polymers we have and this classification is based upon the forces involved in it. Okay, right, next you see, heading you write down rubber, classification is this is done, next is rubber. Okay, there are two types of rubber we have, one is natural, other one is synthetic. Okay, so natural rubber, write down two types of rubber we have, natural and synthetic rubber, natural and synthetic rubber. Natural rubber are those which are available in nature, available in nature. Okay, available in nature and it is obtained from rubber tree, rubber tree and from this we'll get a material we call it as latex material, you must have heard about it. Latex material and from this we obtain rubber. Okay, so it is available in nature basically. Okay, synthetic rubbers are what? These are man-made, synthetic rubbers are man-made. The example of natural rubber is, natural rubber the one example we have is polyisoprene, polyisoprene, okay, polyisoprene. What is the monomer of this? Can you tell me? Isoprene. Isoprene, the structure of isoprene is what? CH2 double bond C, single bond CH3, CH double bond CH2. This is isoprene and when this goes under polymerization it forms polyisoprene. Polyisoprene, the structure is this CH2, C double bond CH3, CH2 and the open end. And this actually you can understand by free radical mechanism this bond pair comes over here, this goes here, this comes over here, this goes here. So this and this forms a double bond here and this is the open end we have this side. So this is the repeating unit. Now can you tell me do this molecule, does this molecule show GI geometrical isomerism? Yes or no? I don't know it's like the groups are all different. No, what is the, you know, condition for a double bond to show geometrical isomerism? There's a condition, okay, and what is that condition? If you have C double bond C and both the carbon has two different group attached, means the group attached at each carbon atom must be different. Then across this double bond we have two isomer possible, cis and trans, okay. This is the condition of double bond to show GI. We can have AB, CD also, but we cannot have AA here. That is not possible. This two must be different. This two must be different. That is what we have here. This is CS3 and obviously this is a different group. It is not CS3 and this carbon has one hydrogen and one different group. So across this double bond we can show, we can say that there is GI possible, geometrical isomerism possible. So it has two form here. One is cis, other one is trans. The cis form of this is soft in nature and the trans one is comparatively hard. This cis form of this molecule only we use in rubber, okay. This is only used in rubber and we call it as heavy rubber, heavy rubber, okay. The trans form is hard in nature. This we do not use in a rubber and we call it as Gattaparcha, G-U-T-A. Must remember this name. G-U-T-A-P-R-C-H-A, okay. So polyisoprene is this. The cis form of polyisomerism, sorry, polyisoprene. The cis form of this is the natural rubber. Done. Yes, sir. Synthetic rubber, manmade rubber. There are many examples. The second one you write down. Synthetic rubber, manmade, okay. So the first example of this is butadiene rubber. Butadiene rubber. Butadiene is the monomer and its structure is what? CH2 double bond CH, single bond CH, double bond CH2. And when you do the polymerization of it, you'll get CH2, CH double bond CH. This is the polymer of this, okay. And this we call it as polybutadiene, polybutadiene, okay. Now the another example of this is neoprene, neoprene. And the monomer of this neoprene is chloroprene. The structure is CH double bond, CCL, CH double bond CH2. The name of this compound is chloroprene, okay. And when you do the polymerization of it, you'll get again the similar way, CH2, CH double bond CHCH2. We have chlorine here. And this is, the name of this one is, since it is chloroprene. So this one is polychloroprene, polychloroprene, which we also call it as neoprene, okay. Then can you go to the next page? Yes, sir. Third example, third one we have is styrene butadiene rubber. Styrene butadiene rubber. Can you tell me the monomer of this? Yeah, what happened? Monomer is what? Monomer is styrene and butadiene. Styrene butadiene rubber. We also write it as SBR in short. Monomers are what? One of the monomer is styrene and we know the structure of styrene we have done already. CH2 double bond CH and here we have a benzene ring. This is styrene. And this combines with butadiene. Butadiene is this CH2 double bond CH, single bond CH, double bond CH2, okay. This we take around 25% in the mixture and this will be 75% in the mixture, okay. And then it forms, under polymerization it forms CH2 CH CH2 CH double bond CH single bond CH2. This is the molecule we get. We also call it as actually when you heat this, we use sodium as a catalyst here, any catalyst in this process. And that is why this molecule is also known as bunas, this BU stands for butadiene. S stands for styrene and N is the catalyst that is sodium. That's why we call it as BUNAS. So the monomer of BUNAS is what? Styrene and butadiene. Catalyst is sodium. Okay. The structure is this. Yes, sir. The fourth one we have a cryonitrile and butadiene rubber. So what is the monomer of this? A cryonitrile and butadiene. The structure of a cryonitrile is what? CH2 double bond CH and here we have CN plus butadiene is CH2 double bond CH, single bond CH, double bond CH2. Heat this in presence of sodium catalyst. The structure is CH2 CH, CN, CH2 CH double bond CH, single bond CH2. That is what we get. And we also call it as BUNA butadiene sodium nitrile, cryonitrile.