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## Basic Science-(Chemistry) (MSBTE-1 Scheme) 3-10 Paints, Vamishes, Insulators, Polymer, Adhesives & Lubricants ### Links at each end join chemically with other similar or different monomers Eventually, linear long chain structure is formed. -M-M-M-M-M-M-M-M- ### On the other hand, monomers po...

## Basic Science-(Chemistry) (MSBTE-1 Scheme) 3-10 Paints, Vamishes, Insulators, Polymer, Adhesives & Lubricants ### Links at each end join chemically with other similar or different monomers Eventually, linear long chain structure is formed. -M-M-M-M-M-M-M-M- ### On the other hand, monomers possess three links in their structure then other monomers can get attached at three different sites. Then there is a network of chain (or cross linking) observed. ### Cross-linked polymers ### On the basis of thermal behaviour - **Name the types of plastics with examples of each.** - **Describe Thermosetting plastic with example.** - **Write characteristics of Thermosetting plastic.** ### There are two types of plastics which are classified depending upon the thermal behaviour. They are: (i) Thermosoftening (ii) Thermosetting. ### (i) Thermosoftening plastics (or Thermoplastics) - Thermosoftening plastics are formed by addition polymerization. They consist of linear long chain polymers without cross-linking. - On heating they become soft and acquire plastic state. At this stage they are moulded to desired shape. On cooling they regain their original properties, becomes hard and loose plasticity. - The hardness is a temporary, subject to change with either increase or decrease in temperature. - This repeated heating and cooling does not change the chemical nature of plastics, it is just like our common sealing wax. - They soften on heating and remain soft till they are hot. They regain on cooling their original hardness (state) and rigidity. - Therefore, thermoplastics can be remoulded or reshaped and reclaimed from waste. - These plastics are soft, weak and less brittle and they can bear low strength due to linear structure of polymer. - Their intermolecular bonding is weak. So they are soluble in organic solvents. **Examples:** Polyethylene. polypropylene, polybutylene, polystyrene, polyvinyl chloride, cellulose nitrate, cellulose acetate. Their structure can be represented as follows : M M-M M MM M- Where, 'M' represents the constituent monomer. ### (ii) Thermosetting plastics - Thermosetting plastics are obtained by condensation polymerization. When heated they become irreversibly into hard and rigid materials. - After cooling, if the set article is heated again it will not soften again, hence it is irreversible. - They are permanent setting plastics, which once set, cannot be reshaped or reused. They acquire three-dimensional cross-liked structure with strong covalent bonds while moulding. - Therefore, they are insoluble in organic solvents. These bonds retain their strength, even on heating.