POLYMERS

INTRODUCTION

  • Polymer word is derived from the word which means many units or parts.
  • Polymers are chemical substances that have a high molecular mass because they are formed by the combination of a large number of simple molecules, known as monomers.
  • The process by which monomers get combined and transformed into polymers is known as polymerization.

 

CLASSIFICATION OF POLYMER – 

Classification of polymers based on their source of origin – 

  1. Natural polymers – These polymers occur naturally. i.e., from plants or animals. Example – Starch, Cellulose, Proteins and Natural rubber.
  2. Synthetic polymers or man-made polymers – Polymers that are being prepared in a laboratory. Example – PVC, orlon, nylon-66, Teflon, etc.
  3. Semisynthetic polymers – These polymers are obtained from modifying natural polymers by some artificial means. Example – vulcanized rubber, rayon, etc.

Classification of polymers based on their structure – 

  1. Linear polymers In these polymer monomers are linked to each other to form a long linear chain. These polymers have high density, high tensile strength, and high melting and boiling points because the linear chains are closely packed in space. Example – high-density polyethylene, nylon, and polyesters.
  2. Branched-chain polymers In these polymer monomers are linked to form long chains in the form of branch chains. And because of this, they are very closely packed and hence have low density, low tensile strength, and low boiling and melting point. Example – low-density polyethylene, glycogen, and starch, etc.
  3. Cross-linked polymers or network polymers In these polymer monomers are linked to form a three-dimensional network. These are hard, brittle, and rigid. Examples – glyptal, Bakelite, etc.

Classification of polymers based on their mode of polymerization –

  • Addition polymers – Polymers are formed by the polymerization of monomers containing double or triple bonds.

Can be further classified into 2 types on the basis of type of monomers – 

  1. HOMOPOLYMERS – Obtained from the polymerization of a single type of monomer.
  2. COPOLYMERS – Obtained from the polymerization of two or more monomer.
  • Condensation polymers These polymers are formed by combining monomers followed by the elimination of small molecules like alcohol, water, etc. Example – nylon 6.

Classification of polymers based on molecular forces – 

  1. Elastomers – These polymers are clenched together by the weakest intermolecular forces; these are rubber-like solid polymers. Example – buna-S, Buna-N, etc. Because of the weak bonding of forces, this polymer can be stretched.
  2. Fibers – These are thread-like and can be woven into fabrics. These polymers are held up by strong intermolecular forces hence have high tensile strength. Example – nylon-66, terylene.
  3. Thermoplastic – These polymers are held up by weak van der Waal’s forces and are linear in nature. They can be converted into suitable shapes by melting. Example – polyethylene, polystyrene.
  4. Thermosetting plastics – These are having low molecular mass and are usually semifluid substances. Examples – Bakelite, melamine.

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