Polymers and Synthetic Materials – NDA Chemistry Notes

Look at the clothes you wear. Look at the water bottle you use. Look at the eraser on your pencil. All of these are made from polymers. Polymers are everywhere in modern life.

This chapter covers what polymers are, how they are made, and the most important synthetic materials asked in NDA.

1. What is a Polymer?

Think of a long chain made of many small identical beads strung together. A polymer is like that chain. Each bead is a monomer.

A polymer is a large molecule made up of many small, repeating units called monomers. The process of joining monomers together to form a polymer is called polymerisation.

Mono = one | Poly = many

Examples from daily life: Plastic bags are made of polythene (a polymer of ethylene). Nylon stockings are made of nylon (a polymer of two different monomers). Rubber gloves are made of rubber (a polymer of isoprene).

Natural polymers also exist. Starch, cellulose, proteins, DNA, natural rubber and silk are all natural polymers.

2. Types of Polymerisation

Addition Polymerisation: In this process, many monomer molecules simply add together to form one long chain. No other product is formed. The monomer must have a double bond (C=C) that opens up to link with the next monomer. The polymer has the same empirical formula as the monomer.

Examples: Ethylene (C₂H₄) → Polyethylene (polythene). Vinyl chloride (CH₂=CHCl) → PVC (polyvinyl chloride). Tetrafluoroethylene (C₂F₄) → Teflon (PTFE). Styrene → Polystyrene.

Condensation Polymerisation: In this process, two different types of monomers join together. A small molecule (usually water) is released as a by-product at each joining step.

Examples: Nylon (adipic acid + hexamethylene diamine release water). Terylene/Dacron (terephthalic acid + ethylene glycol release water). Bakelite (phenol + formaldehyde release water).

3. Classification of Polymers

By origin:

Type	Description	Examples
Natural polymers	Found in nature	Starch, cellulose, natural rubber, proteins, DNA, silk, wool
Semi-synthetic polymers	Made by chemically modifying natural polymers	Rayon (from cellulose), celluloid
Synthetic polymers	Completely man-made from chemicals	Nylon, polyester, PVC, teflon, bakelite, polythene

Rayon is made from natural raw materials (cellulose from wood pulp). It is the only fibre among rayon, nylon, polyester, and polystyrene that is made from natural raw materials.

By behaviour on heating:

Type	Behaviour on Heating	Can it be remoulded?	Examples
Thermoplastic	Softens on heating, hardens on cooling	Yes	Polythene, PVC, nylon, polystyrene, Teflon
Thermosetting	Hardens permanently on heating	No	Bakelite, melamine, urea-formaldehyde resin

Thermoplastics can be recycled because they can be softened and remoulded again. Thermosetting plastics cannot be recycled. Once they are set, they cannot be softened by heating.

4. Important Synthetic Fibres

Nylon

Nylon is the first fully synthetic fibre. It is made by condensation polymerisation. Nylon-6,6 is made from adipic acid and hexamethylenediamine. Nylon-6 is made from caprolactam.

Properties of nylon: Nylon is strong, elastic, and lustrous. It resists moisture and is easy to wash. Uses: Nylon is used in stockings, ropes, parachutes, toothbrush bristles, and gears.

Rayon (Artificial Silk)

Rayon is a semi-synthetic fibre. It is made by chemically processing cellulose from wood pulp. Rayon is also called artificial silk or viscose rayon. [NDA 2010-I] The monomer of rayon is cellulose. [NDA 2010-I]

Rayon is made from natural raw materials (cellulose). It is therefore the only “natural origin” fibre among rayon, nylon, polyester, and polystyrene. Rayon is soft and has a silky appearance. It is used in dresses, sarees, and curtains.

Polyester (Terylene/Dacron)

Polyester is made by condensation polymerisation of terephthalic acid and ethylene glycol. [NDA 2010-I] Terylene and Dacron are trade names for the same polyester material.

Properties: Does not wrinkle easily, dries quickly, strong. Uses: Shirts, sarees, blending with cotton, making plastic bottles (PET bottles).

Polyester is a thermoplastic. It melts instead of burning when heated. [NDA 2010-I]

Acrylic (Orlon)

Acrylic fibre is made from acrylonitrile polymer. Orlon is a trade name for acrylic fibre.

Acrylic fibre is used as a substitute for wool in making synthetic blankets, sweaters, and shawls. Acrylic is cheaper than wool and easier to wash.

5. Important Synthetic Plastics

Polythene (Polyethylene)

Polythene is the most common plastic in everyday life. Plastic bags, containers, and pipes are made from polythene. Polythene is made by addition polymerisation of ethylene (C₂H₄).

There are two types: Low-density polythene (LDPE) is soft and flexible, used for plastic bags and wrapping films. High-density polythene (HDPE) is rigid and tough, used for water pipes, bottles, and containers. Polythene is a thermoplastic.

PVC (Polyvinyl Chloride)

PVC is made by addition polymerisation of vinyl chloride (CH₂=CHCl). Uses: Water pipes, electrical cable insulation, flooring, shoes, raincoats.

PVC is thermoplastic. One hydrogen atom in the ethylene monomer is replaced by a chlorine atom. [NDA 2010-I]

Teflon (PTFE)

Teflon is made by addition polymerisation of tetrafluoroethylene (C₂F₄). Properties: Extremely non-stick. Chemically inert. High heat resistance. Very low friction.

Uses: Non-stick coating on cooking pans. Contact lenses are NOT made from teflon. Contact lenses are made from lucite (polymethyl methacrylate).

Teflon is a thermoplastic polymer. It does not react with almost any chemical substance. This extreme chemical resistance makes it highly useful in industry.

Bakelite

Bakelite is the first man-made synthetic plastic. Bakelite is made by condensation polymerisation of phenol and formaldehyde. [NDA 2010-I]

Bakelite is a thermosetting plastic. It hardens permanently on heating and cannot be remoulded. Uses: Handles of pressure cookers, electrical switches, sockets, and insulators are made from bakelite.

Bakelite is a good electrical insulator. It has high heat resistance. This is why it is used in pressure cooker handles and electrical fittings.

Polystyrene

Polystyrene is made by addition polymerisation of styrene (C₈H₈). Uses: Styrofoam (thermocol) cups, packaging material, disposable plates. Polystyrene is a thermoplastic.

6. Natural Rubber and Vulcanisation

[Image Suggestion: Rubber polymer chains before vulcanisation (separate, sliding chains) and after vulcanisation (linked together by sulphur cross-link bridges into a strong elastic network)]

Natural Rubber: Natural rubber comes from the latex of the rubber tree (Hevea brasiliensis). Latex is a milky white liquid produced by rubber trees in tropical countries (Malaysia, India, Sri Lanka).

Chemical name: Natural rubber is the polymer of isoprene (2-methyl-1,3-butadiene). Natural rubber is soft, sticky, and loses shape when heated. It becomes hard and brittle in cold. It is not useful in these forms.

Vulcanisation: Vulcanisation is the process of heating natural rubber with sulphur to make it stronger, harder, more elastic, and more durable.  Sulphur forms cross-links between rubber polymer chains. These cross-links make the rubber stiffer and stronger. Vulcanised rubber is used in tyres, tubes, shoes, balls, and industrial products.

Why Synthetic Rubber Has Replaced Natural Rubber: Synthetic rubber has largely replaced natural rubber for industrial use because the raw material for synthetic rubber is easily available from petroleum. Natural rubber requires tropical conditions to grow and supply cannot keep up with demand.

Important Synthetic Rubbers:

Name	Monomer	Key Property	Use
Neoprene	Chloroprene	Oil resistant, weather resistant	Wetsuits, hoses, gloves
Buna-S (SBR)	Styrene + Butadiene	Abrasion resistant	Tyres
Buna-N (NBR)	Acrylonitrile + Butadiene	Oil resistant	Oil seals, hoses

7. Kevlar

Kevlar is a very strong synthetic polymer. It is made from two aromatic monomers.

Kevlar is used for making bulletproof jackets and vests. Kevlar is also used in lightweight bicycle frames, helmets, and cut-resistant gloves. Kevlar is much stronger than steel for its weight.

8. Bhopal Gas Tragedy

The Bhopal gas tragedy occurred in December 1984. It was one of the world’s worst industrial disasters.

Methyl isocyanate (MIC) gas leaked from the Union Carbide factory in Bhopal. The Union Carbide factory was producing pesticides (carbaryl/Sevin) when the leak occurred.

Methyl isocyanate is an intermediate chemical used in making pesticides. Thousands of people died and many more were permanently injured.

9. Contact Lenses

Contact lenses are made from lucite (polymethyl methacrylate, PMMA).

Lucite is also called perspex or plexiglass. It is a transparent thermoplastic. Contact lenses are NOT made from teflon, PVC, or polystyrene.

10. Natural Polymers

Natural Polymer	Monomer	Found in
Starch	Glucose	Rice, wheat, potatoes
Cellulose	Glucose	Wood, cotton, paper
Natural rubber	Isoprene	Rubber tree latex
Proteins	Amino acids	Meat, eggs, dal
DNA/RNA	Nucleotides	Nucleus of every living cell
Silk	Amino acids (fibroin)	Silkworm cocoon
Wool	Amino acids (keratin)	Sheep fleece