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## Basic Science-(Chemistry) (MSBTE- - I Scheme) 3-11 ### Thermosetting Plastics - Thermosetting plastics are hard, strong and more brittle as compared to thermosoftening plastics and they cannot be reclaimed from wastes. ### Examples: - Bakelite - Urea formaldehyde - Polyesters - Silicone pla...

## Basic Science-(Chemistry) (MSBTE- - I Scheme) 3-11 ### Thermosetting Plastics - Thermosetting plastics are hard, strong and more brittle as compared to thermosoftening plastics and they cannot be reclaimed from wastes. ### Examples: - Bakelite - Urea formaldehyde - Polyesters - Silicone plastics etc. The structure of thermosetting plastics can be represented as: **M - M - M - M - M - M - M - M - M - M - M - M - M - M - M** **| | | | | | | | | | | | | | | | | |** **M - M - M - M - M - M - M - M - M - M - M - M - M - M - M** **| | | | | | | | | | | | | | | | | |** **M - M - M - M - M - M - M - M - M - M - M - M - M - M - M** **| | | | | | | | | | | | | | | | | |** **M - M - M - M - M - M - M - M - M - M - M - M - M - M - M** Where, 'M' represents the constituent monomer. ### 3.4.3 Distinction between Thermoplastics and Thermosetting Plastics #### Q. Differentiate between thermosetting plastic and thermoplastic. Give specific examples (any four points). (S-14, S-15) #### Q. Distinguish between thermosofting and thermosetting plastics. (S-16, S-17) | Sr. No. | Property | Thermoplastics | Thermosetting plastics | |---|---|---|---| | 1 | Preparation | Thermoplastics are prepared by addition polymerization. | Thermosetting plastics are prepared by condensation polymerization. | | 2 | Structure | They consist of linear long chain polymers with limited cross links. | They consist of three dimensional net work structure joined by strong covalent bonds. | | 3 | Heating effect | They are softened on heating and hence they can be reshaped and reused. | They do not softened on heating, hence they cannot be reshaped and reused. | ### Paints, Varnishes, Insulators, Polymer, Adhesives & Lubricants | Sr. No. | Property | Thermoplastics | Thermosetting plastics | |---|---|---|---| | 4 | Molecular weight | The polymers of thermoplastics have smaller molecular weight. | The polymers of thermosetting plastics have higher molecular weight. | | 5 | Chemical bonding | They are linked by weak covalent bonds. | They are linked by strong covalent bonds. | | 6 | Nature of plastics | Thermoplastics are usually soft, weak and less brittle. | Thermosetting plastics are usually hard, strong and more brittle. | | 7 | Reclaiming | They can be reclaimed from wastes. | They can not be reclaimed from wastes. | | 8 | Solubility | They are soluble in suitable organic solvents as their intermolecular bonds are weak. | They are insoluble in organic solvents as their intermolecular bonds are strong. | | 9 | Examples | Polythene, PVC, polystyrene etc. | Bakelite, polyesters etc. | ### Syllabus Topic: Types of Polymerization Reaction: Addition Polymerization, Condensation Polymerization ### 3.5 Types of Polymerization #### Q. Give the types of polymerization. (W-15) Monomers undergo polymerization by two methods - Types of Polymerization * (i) Addition polymerization * (ii) Condensation polymerization * Fig. 3.5.1