CBSE Class 12 Chemistry Polymer Exam Notes

CBSE Class 12 Chemistry Polymer Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

POLYMER

1. Polymers are high molecular mass substances consisting of a large number of repeating structural units. As polymers are single, giant molecules, i.e. big molecules, they are also called macromolecules.
2. Simple molecules which combine to form polymers are called monomers.
3. The process of formation of polymers from the respective monomers is called polymerisation.

Classification Based On

1. Source of availability

1. Natural polymers: Polymers obtained from nature, mostly plants and animals.
   Examples: Cellulose, starch etc.
2. Synthetic polymers: Polymers prepared in the laboratory.
   Examples: Teflon, Nylon 6,6, synthetic rubber (Buna-S) etc.
3. Semi-synthetic polymers: Polymers derived from naturally occurring polymers by carrying out chemical modifications.
   Examples: Rayon (cellulose acetate), cellulose nitrate etc.

2. Structure of polymer

1. Linear polymers: Polymers consisting of long and straight chains.
   Examples: High density polythene, polyvinyl chloride etc.
2. Branched chain polymers: Polymers containing linear chains having some branches.
   Example: Low density polythene.
3. Cross linked or network polymers: Polymers in which monomer units are cross linked together to form a 3-dimensional network.
   Examples: Bakelite, melamine etc.

3. Mode of polymerisation

1. Addition polymers: Polymers formed by the repeated addition of monomers with double and triple bonds.
   1. Homopolymers: Polymers formed by the polymerisation of a single monomeric species.
      Examples: Polythene, polystyrene.
   2. Copolymers: Polymers formed by addition polymerisation of two different monomers.
      Examples: Buna-S, Buna-N.
2. Condensation polymers: Polymers formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units with elimination of simple molecules.
   Examples: Nylon 6,6, Nylon 6.

4. Molecular forces

1. Elastomers: Polymer chains are held together by the weakest intermolecular forces. These polymers are rubber-like solids with elastic properties.
   Examples: Buna-S, Buna-N, Neoprene.
2. Fibres: Polymers have strong intermolecular forces like hydrogen bonding. Fibres are thread-forming solids which possess high tensile strength and high modulus.
   Examples: Nylon 6,6, polyesters.
3. Thermoplastic polymers: Polymers are held by intermolecular forces which are in between those of elastomers and fibres. These polymers are capable of repeated softening on heating and hardening on cooling.
   Examples: Polythene, polystyrene.
4. Thermosetting polymers: Polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and eventually undergo a permanent set.
   Examples: Bakelite, urea-formaldehyde resins.

1. LDP

Monomer: Ethene – under high temperature and high pressure in the presence of a peroxide initiator as a catalyst.

Uses/Properties: Chemically inert, tough but flexible, poor conductor of electricity; used in squeeze bottles, toys, insulation of wires, flexible pipes.

Classified under: Polythene, addition polymers, thermoplastic polymers, branched polymers, homopolymers.

2. HDP

Monomer: Ethene – in the presence of a hydrocarbon solvent and Ziegler–Natta catalyst (triethylaluminium and titanium tetrachloride), 333 K – 343 K, 6–7 bar.

Uses/Properties: High density due to close packing, chemically inert, more tough and hard. Used in manufacturing of buckets, dustbins, bottles, pipes etc.

Classified under: Addition polymerisation, thermoplastic polymers, linear polymers, homopolymers.

3. Polytetrafluoroethene (Teflon)

Monomer: \(n\,\mathrm{CF_2=CF_2}\) (high pressure, catalyst), tetrafluoroethene

Polymer: \(\left[\,\mathrm{CF_2-CF_2}\,\right]_{n}\) Teflon

Uses/Properties: Chemically inert; used in making oil seals, gaskets, non-stick surface coated utensils.

Classified under: Addition polymers.

4. Polyacrylonitrile

Monomer: \(n\,\mathrm{CH_2=CHCN}\) (peroxide catalyst)

Polymer: \(\left[\,\mathrm{CH_2-\overset{\overset{\mathrm{CN}}{|}}{\mathrm{CH}}}\,\right]_{n}\) Polyacrylonitrile

Uses/Properties: Used as a substitute for wool in making commercial fibres such as orlon and acrilan.

Classified under: Addition polymerisation.

5. Nylon 6,6

Monomer: \(n\,\mathrm{HOOC(CH_2)_4COOH} + n\,\mathrm{H_2N(CH_2)_6NH_2}\) – hexamethylenediamine with adipic acid.

Polymer: \(\left[\,\overset{\overset{\mathrm{H}}{|}}{\mathrm{N}}\mathrm{-(CH_2)_6-}\overset{\overset{\mathrm{H}}{|}}{\mathrm{N}}\mathrm{-}\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}\mathrm{(CH_2)_4-}\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}\,\right]_{n}\) Nylon 6,6

Uses/Properties: Making sheets, bristles for brushes and in the textile industry.

Classified under: Condensation polymerisation, fibres, synthetic polymers, polyamides.

6. Nylon 6

Monomer: Caprolactam with water at a high temperature

Polymer: \(\left[\,\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}\mathrm{-(CH_2)_5-}\overset{\overset{\mathrm{H}}{|}}{\mathrm{N}}\,\right]_{n}\)

Uses/Properties: Manufacture of tyre cords, fabrics and ropes.

Classified under: Condensation polymerisation, fibres, synthetic polymers, polyamides.

7. Dacron

Monomer: Ethylene glycol and terephthalic acid in the presence of zinc acetate: \(n\,\mathrm{HOH_2C-CH_2OH} + n\,\mathrm{HOOC-C_6H_4-COOH}\)

Polymer: Dacron (terylene)

Uses/Properties: Crease resistant; used in blending with cotton and wool fibres, in safety helmets etc.

Classified under: Condensation polymerisation, polyesters, fibres.

8. Bakelite

Monomer: Novolac on heating with formaldehyde

Polymer: Bakelite

Uses/Properties: For making combs, electrical switches, computer discs.

Classified under: Condensation polymerisation, synthetic polymers, thermosetting polymer, cross linked.

9. Melamine formaldehyde polymer

Monomer: Melamine and formaldehyde (HCHO)

Polymer: Melamine polymer

Uses/Properties: For manufacture of unbreakable crockery.

Classified under: Condensation polymerisation of melamine and formaldehyde.

10. Buna-S

Monomer: 1,3-butadiene and styrene: \(n\,\mathrm{CH_2=CH-CH=CH_2}\)

Polymer: \(\left[\,\mathrm{-CH_2-CH=CH-CH_2-CH(C_6H_5)-CH_2-}\,\right]_{n}\)

Uses/Properties: Manufacture of auto tyres, floor tiles, footwear components; resistant to the action of petrol and oil; used in making oil seals, tank lining etc.

Classified under: Copolymerisation, synthetic polymers, elastomer.

11. Natural rubber

Monomer: Isoprene (cis-1,4-polyisoprene): \(\mathrm{H_2C=}\overset{\overset{\mathrm{CH_3}}{|}}{\mathrm{C}}\mathrm{-CH=CH_2}\)

Polymer: Natural rubber

Uses/Properties: Weak van der Waals interactions and has a coiled structure.

Classified under: Copolymerisation, linear polymer, elastomers, rubber.

12. Neoprene / polychloroprene

Monomer: Chloroprene

Polymer: \(\left[\,\mathrm{CH_2-\overset{\overset{\mathrm{Cl}}{|}}{\mathrm{C}}=CH-CH_2}\,\right]_{n}\) Neoprene

Uses/Properties: Manufacturing conveyor belts, gaskets and hoses.

Classified under: Synthetic rubber, chloroprene, elastomer.

13. Buna-N

Monomer: 1,3-butadiene (\(n\,\mathrm{CH_2=CH-CH=CH_2}\)), acrylonitrile (\(\mathrm{CH_2=CHCN}\))

Polymer: \(\left[\,\mathrm{CH_2-CH=CH-CH_2-CH_2-}\overset{\overset{\mathrm{CN}}{|}}{\mathrm{CH}}\,\right]_{n}\) Buna-N

Uses/Properties: Resistant to the action of petrol, lubricating oil and organic solvents. It is used in making oil seals, tank lining etc.

Classified under: Copolymerisation, biodegradable polymers.

14. Poly-β-hydroxybutyrate-co-β-hydroxyvalerate (PHBV)

Monomer: 3-hydroxybutanoic acid and 3-hydroxypentanoic acid.

Polymer: \(\left[\,\mathrm{O-}\overset{\overset{\mathrm{CH_3}}{|}}{\mathrm{CH}}\mathrm{-CH_2-}\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}\mathrm{-O-}\overset{\overset{\mathrm{CH_2CH_3}}{|}}{\mathrm{CH}}\mathrm{-CH_2-}\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}\,\right]_{n}\) PHBV

Uses/Properties: Speciality packaging, orthopaedic devices and controlled release of drugs.

Classified under: Biodegradable polymers.

15. Nylon 2-nylon 6

Monomer: Glycine (\(\mathrm{H_2N-CH_2-COOH}\)) and amino caproic acid (\(\mathrm{H_2N(CH_2)_5COOH}\))

Classified under: Homopolymers, tapes, toys, fibres.

16. Polypropene

Monomer: Propene

Polymer: \(\left[\,\mathrm{CH_2-\overset{\overset{\mathrm{CH_3}}{|}}{\mathrm{CH}}}\,\right]_{n}\)

Uses/Properties: As insulator, wrapping material, manufacture of toys, radio and television cabinets.

17. Polystyrene

Monomer: Styrene

Polymer: \(\left[\,\mathrm{CH_2-\overset{\overset{\mathrm{C_6H_5}}{|}}{\mathrm{CH}}}\,\right]_{n}\)

Uses/Properties: Rain coats, hand bags, water pipes.

Classified under: Linear polymers.

18. PVC

Monomer: Vinyl chloride

Polymer: \(\left[\,\mathrm{CH_2-\overset{\overset{\mathrm{Cl}}{|}}{\mathrm{CH}}}\,\right]_{n}\)

Uses/Properties: Manufacture of paints and lacquers.

19. Glyptal

Monomer: Ethylene glycol, phthalic acid

Polymer:

Uses/Properties: Not specified.

Addition polymerisation or chain growth polymerisation:

The most common mechanism for addition polymerisation reactions is the free radical mechanism.

Step 1: Chain initiating step

\[\underset{\text{Benzoyl peroxide}}{\mathrm{C_6H_5-\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}-O-O-\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}-C_6H_5}} \longrightarrow 2\,\mathrm{C_6H_5-\overset{\overset{\mathrm{O}}{\Vert}}{\mathrm{C}}-O^{\bullet}} \longrightarrow 2\,\underset{\text{Phenyl radical}}{\mathrm{C_6H_5^{\bullet}}} + 2\,\mathrm{CO_2}\] \[\mathrm{C_6H_5^{\bullet}+CH_2=CH_2\longrightarrow C_6H_5-CH_2-\overset{\bullet}{C}H_2}\]

Step 2: Chain propagating step

\[\mathrm{C_6H_5-CH_2-\overset{\bullet}{C}H_2+CH_2=CH_2\longrightarrow C_6H_5-CH_2-CH_2-CH_2-\overset{\bullet}{C}H_2}\] \[\longrightarrow\ \mathrm{C_6H_5-(CH_2-CH_2)_n-CH_2-\overset{\bullet}{C}H_2}\]

Step 3: Chain terminating step

\[\mathrm{C_6H_5-(CH_2-CH_2)_n-CH_2-\overset{\bullet}{C}H_2}\ +\ \mathrm{C_6H_5-(CH_2-CH_2)_n-CH_2-\overset{\bullet}{C}H_2}\ \longrightarrow\ \underset{\text{Polythene}}{\mathrm{C_6H_5-(CH_2-CH_2)_n-CH_2-CH_2-CH_2-CH_2-(CH_2-CH_2)_n-C_6H_5}}\]

Vulcanisation of rubber

Heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.

Write an equation for the chemistry involved when a drop of hydrochloric acid makes a hole in nylon stockings.

Answer: The amide bond (−CO−NH−) in nylon gets hydrolysed by the acid, so the polymer chain breaks.

Fibres are of crystalline structure. Why?

Answer: Fibres have strong intermolecular forces of attraction, which lead to close packing of their chains and impart a crystalline structure.

Which artificial polymer is present in bubble gum or chewing gum?

Answer: Bubble gum or chewing gum contains synthetic styrene-butadiene rubber.

Name the polymer used for making medicinal capsules.

Answer: PHBV, i.e. poly-β-hydroxybutyrate-co-β-hydroxyvalerate.

Which colligative property is used to determine the molecular masses of polymers?

Answer: Osmotic pressure is the colligative property used to determine the molecular masses of polymers.

How do the double bonds in the rubber molecule influence its structure and reactivity?

Answer: Due to the presence of double bonds, the rubber molecule has the cis configuration, so the chains cannot pack closely and are held together only by weak van der Waals forces. The double bonds are also the reactive sites where sulphur forms cross links during vulcanisation.

Why are the numbers 6, 6 and 6 put in the names nylon-6,6 and nylon-6?

Answer: Both the monomers of nylon-6,6, namely hexamethylenediamine and adipic acid, contain six carbon atoms each. The number 6 in nylon-6 indicates that its monomer, caprolactam, has six carbon atoms in its molecule.

Can a copolymer be formed in both addition and condensation polymerisation or not? Explain.

Answer: Yes. Though copolymers are mostly addition polymers like styrene-butadiene rubber and butyl rubber, the term can be used for condensation polymers also, for example:

1. Addition polymerisation of styrene and butadiene forms the copolymer styrene-butadiene rubber.

\[n\,\mathrm{CH_2=CH-CH=CH_2} + n\,\mathrm{C_6H_5CH=CH_2} \longrightarrow \left(\mathrm{-CH_2-CH=CH-CH_2-}\right)_n\left(\mathrm{-CH_2-\overset{\overset{\mathrm{C_6H_5}}{|}}{\mathrm{CH}}-}\right)_n\]

2. Condensation polymerisation of hexamethylenediamine and adipic acid forms nylon-6,6.

\[n\,\underset{\text{adipic acid}}{\mathrm{HOOC-(CH_2)_4-COOH}} + n\,\underset{\text{hexamethylenediamine}}{\mathrm{H_2N-(CH_2)_6-NH_2}} \xrightarrow{-\,2n\,\mathrm{H_2O}} \left(\mathrm{-NH(CH_2)_6-NH-CO-(CH_2)_4-CO-}\right)_n\]

Arrange the following polymers in increasing order of their intermolecular forces:

1. nylon-6,6, Buna-S, polythene
2. nylon-6, neoprene, polyvinyl chloride

Answer:

1. Buna-S < polythene < nylon-6,6
2. Neoprene < polyvinyl chloride < nylon-6

Explain the difference between Buna-S and Buna-N.

Answer: Buna-N is a copolymer of 1,3-butadiene and acrylonitrile, whereas Buna-S is a copolymer of 1,3-butadiene and styrene.

Why should we always use the purest monomer in the free radical mechanism?

Answer: The monomer has to be as pure as possible because the presence of any other molecule during free radical polymerisation can act as a chain initiator or inhibitor, which will interfere with the normal polymerisation reaction.

Students can revise the concepts quickly using these notes for CBSE Class 12 Chemistry Polymer Exam Notes.