 Next, we have to discuss about the one last classification of polymers that is based on right down classification based on molecular forces based on molecular forces based on molecular forces. So depending upon the strength of the force that is involved in the polymers, this classification is done. Okay, and it is important. The first one is lastomers. The first one is elastomers. Write down into this. In short, you write down these are the polymers in which the intermolecular force of attraction is very weak. Elastomers, in short, write down point wise. IMF, that is intermolecular force. So IMF is weakest here. And when IMF is weakest, so obviously the polymers can slide over the layer. Okay, we have layer by layer structure. So when intermolecular force is weak, then they then all these layer can slide onto each other, right? So that's why they have elasticity property. They have high degree of elasticity, high degree of elasticity. And what we say they have ability to stretch over their normal length, actually 10 times of their normal length, they can stretch, but that is not important. Okay, they have the structure is irregular, write down irregular shape, irregular shape we have. And few cross links are there. And few cross links. Okay, example you write down. Examples of elastomers are natural rubber, natural rubber. Examples. Buna S. You know what is Buna S? You do not know. Okay, Buna S is a copolymer. We'll discuss that. Buna S is a copolymer. We'll discuss that. Rubber when we do rubber, we'll discuss into that. Let's write down the example now. Okay, Buna S. So vulcanized rubber also here we take as this thing, elastomers. Vulcanized rubber is important. They have asked this question many times in the exam, vulcanized rubber. So in this only, we'll discuss what is vulcanized rubber. So write down the heading, write down, write down the vulcanization is a process, excuse me, vulcanization is a process by which by which the tensile strength, elasticity, the tensile strength, elasticity and resistance of natural rubber can be increased. Can be increased. Okay. Next line. In this process, in this process, the rubber is heating with sulfur, heating with sulfur. And in bracket you write down after sulfur, we use 3 to 5% of sulfur means the rubber is heating with 3 to 5% of sulfur. During vulcanization, the sulfur bridges, the sulfur bridges or the cross links, sulfur bridges or the cross links or the cross links forms between the polymer chain. And this is known as vulcanized rubber. This is known as vulcanized rubber. So basically, the natural rubber you have, suppose the rubber, natural rubber is this, we have different, you know, chain. In this we have natural rubber is this, suppose this is natural rubber. And when you heat this with 3 to 5% sulfur, then there will be a cross link of sulfur bridge between the polymer chain. Like this, suppose the chain we have. So all these will have sulfur bridges present between this. And that is how the strength increases, the resistance increases. Like this, the chain forms. Okay. So this rubber, we call it as vulcanized rubber. This is natural rubber. So this vulcanized rubber they have asked many times in the exam, competitive exam also they have asked, in board exam also they have asked. Okay. So but there's only one thing you need to keep in mind that the natural rubber is heated with 3 to 5% sulfur to give the rubber which has more tensile strength, resistance and all that rubber we call it as vulcanized rubber. Generally, the question that they ask in competitive exam, in vulcanization the rubber is heated with what? We'll have four options, sulfur is the answer. Okay. So that is one type of, you know, first classification of molecular, based on molecular forces we have of polymers. Okay. Second one, write down is fiber, is fiber, fiber write down. In this the intermolecular, here you see intermolecular forces weakest here. And here the intermolecular force in fiber is the strongest. Okay. IMF strongest here. Write down. The forces involved in this, next line, the forces involved write down hydrogen bonding or dipole-dipole interaction. Dipole-dipole interaction. Like in case of polyamides, nylons are polyamides. That also you must remember. Nylons are polyamides. Amide linkage is there. So in case of polyamides, the intermolecular force are due to hydrogen bonding. You must remember this. Polyamide may we have hydrogen bonding. But when you have polyesters, like terylene dichron that you have, polyesters, we have, we have dipole-dipole interaction. In polyester and polyacrylonitrile, that is orlone, see polyester is, see polyester is, is dichron and polyacrylonitrile is orlone. See in both we have dipole-dipole interaction. This you must remember for both the things. Dipole-dipole interaction. So in all these comes under the category of fibers. Okay. They are very strong in terms of their strength. Okay. So when intermolecular forces are strong, they have obviously high tensile strength, the property. They have high tensile strength. Okay. And less elasticity. Separate tendency is not there. Hence, less elasticity. And the last thing to write down, they have high melting point, high melting point and low solubility. Examples must important. Fibres, the examples are dichron, orlone and polyamides. Okay. Fine. Yes, sir. Okay. So fibers we have done. Next you write down thermoplastic. The third type, we have thermoplastics. Write down the polymers in which the polymers in which the intermolecular force, the polymers in which the intermolecular force of attraction are in between elastomers and fibers. The intermolecular force of attraction are in between elastomers and fibers. So moderate we have here. These are linear polymers. These are linear polymers hard at room temperature. These are linear polymers hard at room temperature and become soft and viscous on heating, become soft and viscous on heating and again become rigid on cooling. They become soft and viscous on heating and again become rigid in cooling. Okay. Example you write down. Example you write down polythene, polypropylene, polystyrene, PVC, Teflon, polyacrylonitrile. There's a term that we use here is plasticizers. Okay. Write down that term in this only, plasticizers. Definition of plasticizers you write down. Those plastics, those plastics which do not soft, which do not get soft, very much on heating. Those plastics which do not get soft very much on heating can be made soft and workable by addition of certain organic compound called plasticizers. Those plastics which do not get soft very much on heating can be made soft and workable by the addition of certain organic compounds called plasticizers. Okay. There are some examples of plasticizers. You must remember dialkyl, dialkyl thalates, dialkyl p-h-t-h-a-l-a-t-e-s is the one kind of plasticizers. Okay. Examples you must remember. But next I will write down PVC. PVC is extremely stiff. PVC polyvinyl chloride is extremely stiff and hard, extremely stiff and hard. But the addition of di-nbutyl phthalate, this one, di-nbutyl p-h-t-h-a-l-a-t-e. This is the general name. This one is specific example we are taking. PVC is extremely stiff and hard, but the addition of di-almageol phthalate, in short, in bracket you write down, we also call it as DBP, di-nbutyl phthalate, makes it soft and rubber-like. Makes it soft and rubber-like. Okay. Di-octyl phthalate is another example. Di-octyl p-h-t-h-a-l-a-t-e, in short, we write it DOP, is the another example of this plasticizers. Okay. Structure of this you see, thalic acid is this, benzene ring, and we have COOH here, but that H you remove by butyl group, C4H9. It becomes DBP, C4H9. Okay. Octyl is what? C8H17, you need to put here. So, this is the structure of octyl. COOH, C8H17, COOH, C8H17. This is DOP, and this is DBP. This supply size, you must remember. So, this is one thing. Cracyl phosphate also we use as a plasticizers. Another example, the last one you write down, Cracyl phosphate. The structure is this, ME, and here we have OP double bond OOH double bond O. This is ortho-cracyl phosphate. Another plasticizers. Okay. So, these three examples you must remember.