Chapter 15 Polymers Class 12 Chemistry Notes For CBSE Students
15.1 What are polymers?
Ans: The word polymer has a Greek origin where poly means many and mers or meros stands for unit or part.
Thus, Polymers are high molecular mass substances consisting of large numbers of repeating structural units. They are also called as macromolecules. Some examples of polymers are polythene, bakelite, rubber, nylon 6, 6, etc.
15.2 How are polymers classified on the basis of structure?
Ans: On the basis of structure, polymers are classified into three types. These are linear chain polymers, branched chain polymers and crossedlinkedpolymers.
(i) Linear Chain Polymers: In this case, the monomer units are linked to one another to form long linear chains. These linear chains are placed one above the other and are closely packed in space. The close packing results in high densities, tensile strength and also high melting and boiling points. High density polyethene is a very common example of this type. Nylon, polyesters and PVC are also linear chain polymers.
(ii) Branched-Chain Polymers: In which the monomers not only join in a linear fashion but also form branches of different lengths along the main chain. For ex: LDPE, glycogen, etc.
(iii) Cross-Linked Polymers: In which the initially formed linear polymer chains join together to form a 3D network structure. For ex: bakelite, Urea-formaldehyde resin, etc.
15.3 Classify the following as addition and condensation polymers: Terylene, Bakelite, Polythene, Teflon.
Ans:
- Condensation polymer
- Condensation polymer
- Addition polymer
- Addition polymer
15.4 Explain the difference between Buna-N and Buna-S.
Ans: Buna – N
Constituents are : buta-1, 3-diene and acrylonitrile.
Buna – N is a copolymer of 1,3−butadiene and acrylonitrile. It is also called Nitrile rubber (NBR). It is obtained by polymerization of 1,3-butadiene and acrylonitrile in the presence of sodium .It is used for making oil seels, manufacturing of tank linings, protective gloves etc.
Buna − S
Buna – S is a copolymer of 1,3−butadiene and styrene. It is obtained by polymerization of 1,3-Butadiene and styrene in the ratio 3:1 in the presence of sodium.
In Buna – S, Bu stands for butadiene, Na for sodium and S for styrene. It is also called SBR (Styrene Butadiene Rubber).It has slightly less tensile strength than natural rubber. It is used for making automobile tyres, rubber soles, belts, hoses etc.
15.5 Arrange the following polymers in increasing order of their intermolecular forces.
Nylon 6,6, Buna-S, Polythene.
Ans: On the basis of intermolecuiar forces, polymers are classified as elastomers, fibres and plastics. The increasing order of intermolecuiar forces is: Elastomer < Plastic < Fibre
- Elastomers- They have elastic character and have weak intermolecular forces. Example – natural rubber.
- Fibres- They have strong hydrogen bond or dipole- dipole interactions between polymers chain. Example – nylon 66.
- Thermoplastics- They have intermolecular forces intermediate between elastomers and fibres. Example – polythene.
- Thermosetting polymers- They undergoes permanent change on heating. Example – bakelite.
Buna − S < Polythene < Nylon 6, 6
15.6 Write the names of monomers of the following polymers:
Ans: (i) Hexamethylene diamine NH2-(CH2)6NH2 and adipic acid HOOC – (CH2)4 – COOH
(ii) Caprolactum
(iii) Tetrafluoroethene F2C = CF2
