CBSE Class 12 Chemistry Chapter 29 Polymers NCERT Solutions

Solution: Polymers are defined as large molecules, or macromolecules, that are composed of numerous repeating structural units. These units, known as monomers, are chemically bonded together to form a long chain. Polymers possess very high molecular masses, typically ranging from $10^3$ to $10^7$ atomic mass units (u). The monomers are linked by strong covalent bonds. Polymers can occur naturally, such as rubber and cellulose, or be synthesized artificially, like polythene and nylon 6, 6.

Solution: Polymers can be classified into three main types based on their structural arrangement:

1. Linear polymers: These polymers consist of long, straight, and unbranched chains. They can be represented schematically as a series of repeating units in a line. Examples include high-density polythene (HDP) and polyvinyl chloride (PVC).

   

2. Branched chain polymers: These polymers are characterized by a main polymer chain that has shorter side chains or branches attached to it. They can be visualized as a primary chain with offshoots. Low-density polythene (LDP) and amylopectin are examples.

   

3. Cross-linked or Network polymers: In these polymers, the linear or branched chains are interconnected by covalent bonds, forming a three-dimensional network structure. This cross-linking often involves monomers that are bi-functional or tri-functional. Examples include bakelite and melmac.

   

Solution:

1. The polymer represented by $$\backslash left\backslash \{\backslash operatorname\{CF\}\_\{2\}-\backslash operatorname\{CF\}\_\{2\}\backslash right\backslash \}\_\{n\}$$ is Polytetrafluoroethene (Teflon). Its monomer is Tetrafluoroethene, with the chemical formula $$\backslash operatorname\{CF\}\_\{2\}=\backslash operatorname\{CF\}\_\{2\}$$.
2. Nylon 6,6 is a copolymer formed from two different monomers: Hexamethylenediamine, which has the structure $$\backslash left[H\_2N-\backslash left(CH\_2\backslash right)\_6-NH\_2\backslash right]$$, and Adipic acid, with the structure $$\backslash left[HOOC-\backslash left(CH\_2\backslash right)\_4-COOH\backslash right]$$.
3. The polymer formed from Caprolactam is Nylon 6. Therefore, the monomer is Caprolactam itself, which is a cyclic amide.

   

Solution: The classification of the given polymers is as follows:

Addition polymers: These polymers are formed by the repeated addition of monomer molecules without the loss of any by-products. The monomers usually contain double or triple bonds.

• Polyvinyl chloride: Formed from the addition polymerization of vinyl chloride monomers ($CH\_2=CHCl$).

  

• Polythene: Formed from the addition polymerization of ethene monomers ($CH\_2=CH\_2$).

  

Condensation polymers: These polymers are formed when monomers react with each other with the elimination of small molecules like water, ammonia, or methanol.

• Terylene: Also known as Dacron, it is formed by the condensation reaction between ethylene glycol and terephthalic acid, with the elimination of water molecules.

  

• Bakelite: It is a thermosetting polymer formed by the condensation reaction between phenol and formaldehyde, resulting in a cross-linked network structure.