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NCERT Exemplar · Class 12 · Chemistry

Chapter 15: Polymers

Practice each question, then open the answer or worked solution.

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Long Answer Questions

5 questions
Q53Written answer

Synthetic polymers do not degrade in the environment for a long time. How can biodegradable synthetic polymers be made. Differentiate between biopolymers and biodegradable polymers and give examples of each type.

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Ans: 1.Poly-hydroxybutyrate-co-β-hydroxyvalerate (PHBV)

It's made by copolymerization 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. PHBV is used in specialty packaging, orthopaedic devices, and controlled drug release. In the environment, PHBV is degraded by bacteria.

2. Nylon 2-Nylon 6: It is a biodegradable alternating polyamide copolymer of glycine and amino caproic acid.

Biopolymers are natural polymers found in plants and animals such as protein, fat, cellulose, and so on.

Biodegradable polymers are polymers that contain functional groups that are similar to those found in biopolymers. They are not resistant to the processes of environmental degradation.


Q54Written answer

Differentiate between rubbers and plastics on the basis of intermolecular forces.

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Ans: In rubber, the polymer chain are held together by weakest force of attraction. While, in plastic, the strong intermolecular force of attraction is present between elastomers and fibres.

In rubber, a few crosslinks are introduced between the chain, while plastics are linear or slightly branched molecules which gets soft on heating and hard on cooling.


Q55Written answer

Phenol and formaldehyde undergo condensation to give a polymer (A) which on heating with formaldehyde gives a thermosetting polymer (B). Name the polymers. Write the reactions involved in the formation of (A). What is the structural difference between two polymers?

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Ans: The oldest synthetic polymers are phenol-formaldehyde polymers. These are made by combining phenol and formaldehyde in the presence of either an acid or a base catalyst. The reaction begins with the formation of o-and/or p hydroxymethyl phenol derivatives, which then react with phenol to form compounds with shaving rings connected by –CH2 groups. The first product could be a linear product, such as Novolac.

When heated with formaldehyde, Novolac crosslinks to form Bakelite, an infusible solid mass.

It is used to make combs, phonograph records, electrical switches, and utensil handles.

The polymer A is Novolac and polymer B is Bakelite. 


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Q56Written answer

Low density polythene and high density polythene, both are polymers of ethene but there is marked difference in their properties. Explain.

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Ans:

LDP 

HDP

1. It is obtained by polymerizing ethene under high pressures of 1000 to 2000 atmospheres at temperatures ranging from 350 K to 570 K in the presence of traces of dioxygen or a peroxide initiator (catalyst).

1. It is formed when ethene is added polymerised in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler Natta catalyst) at temperatures ranging from 333 K to 343 K and pressures ranging from 6-7 atmospheres.

2. LDP has a highly branched structure as a result of free radical addition and H-atom abstraction.

2. HDP is made up of linear molecules and has a high density as a result of close packing.

3. Low density polythene is chemically inert, tough, and flexible, but it is a poor conductor of electricity.

3. It is also chemically inert and tougher than sand.


Q57Written answer

Which of the following polymers soften on heating and harden on cooling? What are the polymers with this property collectively called? What are the structural similarities between such polymers? Bakelite, urea-formaldehyde resin, polythene, polyvinyl, polystyrene.

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Ans: Thermoplastic polymer

Thermoplastic polymers are linear or slight branched-chain polymers. In this type of polymer, the strong intermolecular force of attraction is present between elastomers and fibers. This type of polymer softens on heating and hardens on cooling. For example, polythene, polystyrene and polyvinyl.


Thermosetting polymer

Thermosetting polymers are cross-linked polymers. These polymers on heating undergo cross-linking in molds. They become infusible on heating so, cannot be reused again. For example, Bakelite and urea-formaldehyde resins.