Polymers and Biopolymers
Science & Technology › Chemistry in Daily Life and Biomolecules · Topic 7.1
A polymer is a very large molecule made by joining many small repeating units called monomers through a process called polymerisation. Polymers may be natural, such as cellulose, starch, proteins, natural rubber and DNA, or synthetic, such as polythene, PVC, nylon and Teflon. Addition polymers, such as polythene, form when monomers with double bonds add to each other without losing atoms, and condensation polymers, such as nylon and polyester, form with loss of a small molecule such as water. Thermoplastics soften on heating and can be remoulded, while thermosetting plastics such as Bakelite harden permanently. Biopolymers are polymers made by living organisms or from renewable sources, and biodegradable plastics such as polylactic acid aim to reduce plastic pollution.
5 min read · UPSC Prelims · Science & Technology · Chemistry in Daily Life and Biomolecules
At a Glance
- Polythene Ethene monomer; addition
- Nylon Condensation polymer
- Teflon PTFE; non-stick
- Bakelite Thermosetting plastic
- Bioplastic Polylactic acid (PLA)
- Exam link UPSC Prelims, Science & Technology: Chemistry in Daily Life and Biomolecules
Where Does It Fit?
This is the first topic of the macro on chemistry in daily life and biomolecules. It starts with large molecules that make plastics, fibres and rubber, and links to biological polymers described later. Previous topic: Characteristics of Solutions. Next topic: Chemistry of Pharmaceuticals.
Which Synthetic Polymers Should You Know?
| Polymer | Monomer, type and uses |
|---|---|
| Polythene | Ethene. Addition. Low-density for films and bags, high-density for pipes and bottles |
| Polypropylene | Propene. Addition. Ropes, containers and fabrics |
| PVC | Vinyl chloride. Addition. Pipes, cables and flooring |
| Polystyrene | Styrene. Addition. Thermocol and packaging |
| Teflon | Tetrafluoroethene. Addition. Non-stick coatings |
| Perspex | Methyl methacrylate. Addition. Clear sheets and lenses |
| Nylon-6,6 | Hexamethylenediamine and adipic acid. Condensation. Fibres and ropes, developed by Wallace Carothers in 1935 |
| Polyester | Terephthalic acid and ethylene glycol. Condensation. Clothing and PET bottles |
| Bakelite | Phenol and formaldehyde. Condensation. Thermosetting, used in switches and handles, invented by Leo Baekeland in 1907 |
What Are Natural Polymers and Rubber?
- Cellulose: a polymer of glucose in plant cell walls and cotton, used for paper and rayon.
- Starch: a polymer of glucose that plants store as food.
- Proteins and nucleic acids: polymers of amino acids and nucleotides, as in Biomolecules: Carbohydrates, Proteins, Lipids, Nucleic Acids.
- Natural rubber: a polymer of isoprene from latex of the rubber tree. Charles Goodyear found vulcanisation in 1839, heating rubber with sulphur to make it strong and elastic.
- Synthetic rubber: Buna-S from butadiene and styrene, used in tyres, and neoprene.
- Silk and wool: natural protein fibres, and Kevlar is a strong synthetic fibre used in bulletproof vests.
What Are Biopolymers, Plastic Waste and What Else Should You Remember?
- Biopolymers: polymers from living sources or renewable raw materials, such as starch-based plastics, polylactic acid from corn or sugarcane, polyhydroxybutyrate from bacteria and chitosan from crab shells.
- Biodegradable plastics: break down by microbes into water and carbon dioxide, but only under proper composting conditions, so they are not a full solution.
- Plastic pollution: plastics last for hundreds of years, break into microplastics and harm marine life, and enter food chains, as in the topic of environment and ecology.
- Plastic Waste Management Rules: India issued rules in 2016 and amended them in 2021 and 2022. A ban on identified single-use plastic items took effect on 1 July 2022, and extended producer responsibility makes producers responsible for waste.
- Recycling codes: numbers 1 to 7 on plastic items show the type of resin, with 1 for PET and 2 for HDPE.
- Thermoplastic and thermoset: thermoplastics such as polythene can be recycled by melting, while thermosets cannot.
- Silicones: polymers with silicon-oxygen chains, used in sealants and medical implants, as in Carbon and Its Allotropic Forms.
- Conducting polymers: Hideki Shirakawa, Alan MacDiarmid and Alan Heeger received the Nobel Prize in 2000 for them.
- Addition polymerisation: addition polymerisation needs an initiator such as a peroxide, and it can proceed by a free radical chain mechanism, as in the making of low-density polythene at high pressure.
- Fibres: natural fibres include cotton, wool and silk, semi-synthetic fibres include rayon, and synthetic fibres include nylon, polyester and acrylic.
- Degree of polymerisation: the properties of a polymer depend on the length of its chains and on branching and cross-linking, so high-density and low-density polythene differ.
- Rubber industry: India produces natural rubber mainly in Kerala, and the Rubber Board supports the sector.
- Plastic types in daily life: PET is used for bottles, HDPE for milk cans, PVC for pipes, LDPE for carry bags, polypropylene for caps and polystyrene for cups, and knowing the type helps in sorting for recycling.
- Natural versus synthetic: natural polymers are produced by living organisms, are usually biodegradable and have complex structures, while synthetic polymers are made in factories and are designed for specific properties.
Why Does It Matter for the Exam?
- Matching questions: polymer with monomer and use.
- Concept questions: addition versus condensation, thermoplastic versus thermosetting.
- Policy questions: plastic waste rules, single-use plastic ban and extended producer responsibility.
- Current affairs link: global plastic treaty talks and bioplastic start-ups.
- Common errors: believing that biodegradable always means compostable at home.
As an analytical point, polymers make modern life possible but their waste is a global problem. Reduction, reuse and recycling, backed by rules for producers, matter more than substitution alone.
Why Is This Topic Important?
- Facts Monomers and uses asked
- Concept Addition and condensation
- Policy Plastic rules
What Came Next?
The next topic covers the chemistry of pharmaceuticals. Next topic: Chemistry of Pharmaceuticals.
Key People and Terms
- Polymer Large molecule of repeating units
- Monomer Small repeating unit
- Vulcanisation Heating rubber with sulphur
- Thermoplastic Softens on heating
- Bioplastic Plastic from renewable sources
- EPR Extended producer responsibility
Exam Corner
Points to Remember
- Polythene: ethene; PVC: vinyl chloride.
- Nylon-6,6 by Carothers.
- Bakelite is thermosetting.
- Single-use plastic ban: 1 July 2022.
- Vulcanisation: Goodyear.
Do Not Confuse With
- Thermoplastic and thermoset Remoulds versus sets permanently
- Addition and condensation polymer No byproduct versus small molecule lost
- Biodegradable and bio-based Breaks down versus from renewable source
Memory Hook
Ethene makes polythene, vinyl chloride PVC; nylon by condensation, Bakelite sets for good; single-use ban in twenty-two, PLA in the wood.
Mains Angle
Questions link polymers with the plastic waste problem. These points add depth.
- Types Natural and synthetic
- Use Plastics, fibres, rubber
- Issue Plastic waste
A Question You May Face
An original practice question, not a past paper question.
“Classify polymers with examples and discuss the problem of plastic pollution and the role of biodegradable alternatives.”
How to Answer
- Types Natural, synthetic.
- Methods Addition, condensation.
- Waste Rules.
- Options Bioplastics.
GS Relevance
Frequently Asked Questions
What is a polymer?
A polymer is a large molecule made of many repeating small units called monomers joined by chemical bonds. Natural polymers include cellulose, proteins and rubber, while synthetic polymers include polythene, PVC, nylon and polyester, and polymers have a wide range of uses from plastics and fibres to rubber.
What is the difference between addition and condensation polymers?
Addition polymers, such as polythene and PVC, form when monomers with double bonds join one after another without losing any atoms. Condensation polymers, such as nylon and polyester, form when monomers join with the loss of a small molecule such as water at each step.
What is the difference between thermoplastics and thermosetting plastics?
Thermoplastics such as polythene and PVC soften on heating and harden on cooling, so they can be remoulded and recycled. Thermosetting plastics such as Bakelite and melamine harden permanently when heated for the first time and cannot be softened again, so they are used where heat resistance is needed.
What is vulcanisation?
Vulcanisation is the heating of natural rubber with sulphur, discovered by Charles Goodyear in 1839. The sulphur forms cross-links between the polymer chains, which makes the rubber harder, stronger, more elastic and less sticky, so it is used for tyres.
What are biodegradable plastics?
Biodegradable plastics, such as polylactic acid and polyhydroxybutyrate, are plastics that microbes can break down into water, carbon dioxide and biomass. Many need the heat and conditions of industrial composting, so they are not a full solution to plastic pollution, and reducing use remains important.
PYQ Practice — Statement Analysis
1 Polythene is made from ethene monomers.
An addition polymer.
2 Bakelite is a thermoplastic that can be remoulded.
It is thermosetting.
3 Nylon-6,6 is a condensation polymer.
Developed by Carothers.
4 Vulcanisation uses sulphur to cross-link rubber.
By Goodyear in 1839.
Past Mains Questions on This Topic
This topic comes under Chemistry in Daily Life and Biomolecules. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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