CBSE Class 12 Chemistry Polymers Questions

VSA TYPE QUESTIONS (1 - MARK QUESTIONS)

Question 1. Define the term copolymer.
Answer: A polymer made up of more than one species of monomer units is called a copolymer. For example, Buna-S is a copolymer formed by the copolymerization of 1,3-butadiene and styrene.
In simple words: Polymers formed from two or more different types of monomers are called copolymers.

Exam Tip: Always give an example like Buna-S or Buna-N when defining a copolymer to secure full marks.

Question 2. Identify homopolymer from the following examples Nylon-66, Nylon-6, Nylon- 2-Nylon-6.
Answer: Nylon-6 is a homopolymer because it is obtained from a single type of monomer unit, namely caprolactam. On the other hand, Nylon-66 and Nylon-2-Nylon-6 are copolymers as they are formed from two different types of monomers.
In simple words: Homopolymers contain only one kind of repeating monomer unit.

Exam Tip: Remember that nylon polymers with two numbers (like Nylon-6,6) are polyamides formed from two monomers, hence copolymers.

Question 3. Give example of a natural polyamide which is an important constituent of diet.
Answer: Proteins are natural polyamides that serve as an essential constituent of our diet.
In simple words: Proteins are natural polymers made of amino acids linked by peptide bonds.

Exam Tip: Peptide bonds are essentially amide linkages, which categorizes proteins as natural polyamides.

Question 4. Classify polythene and bakelite as thermosetting plastics or thermoplastics.
Answer: Polythene is a thermoplastic polymer (softens on heating and hardens on cooling), whereas bakelite is a thermosetting polymer (cannot be softened on heating once molded).
In simple words: Thermoplastics melt when heated, while thermosetting plastics set permanently.

Exam Tip: Thermoplastics have weak intermolecular forces between linear chains, whereas thermosets have extensive cross-linking.

Question 5. Among fibres, elastomers and thermosetting polymers, which one has strongest intermolecular forces of attraction?
Answer: Fibres have the strongest intermolecular forces of attraction due to strong hydrogen bonding or dipole-dipole interactions, which lead to close packing and high crystallinity.
In simple words: Fibres are tightly held together by strong forces, making them rigid and strong.

Exam Tip: Elastomers have the weakest forces (allowing stretching), followed by thermoplastics, and fibres have the strongest.

Question 6. Why is bakelite called a thermosetting polymer.
Answer: Bakelite is called a thermosetting polymer because it undergoes extensive cross-linking on heating to form a three-dimensional infusible and insoluble network that cannot be softened or remolded upon reheating.
In simple words: It permanently hardens when heated during formation and cannot be melted again.

Exam Tip: Mention cross-linking and 3D network structure to get full credit.

Question 7. Give the monomers of bakelite.
Answer: The monomers of bakelite are phenol and formaldehyde.
In simple words: Phenol and formaldehyde react together to form this polymer.

Question 8. Identify the monomer in the following polymeric structure.
\(\left[ -\text{CO}-(\text{CH}_2)_4-\text{CO}-\text{NH}-(\text{CH}_2)_6-\text{NH}- \right]_n\)
Answer: The given polymer is Nylon-6,6. Its monomers are:
1. Adipic acid: \(\text{HOOC}-(\text{CH}_2)_4-\text{COOH}\)
2. Hexamethylenediamine: \(\text{H}_2\text{N}-(\text{CH}_2)_6-\text{NH}_2\)
In simple words: Nylon-6,6 is made from a 6-carbon diacid and a 6-carbon diamine.

Exam Tip: Break the amide bond (\(-\text{CO}-\text{NH}-\)) and add hydroxyl (\(-\text{OH}\)) to the carbonyl carbon and hydrogen (\(-\text{H}\)) to the nitrogen to find the parent monomers.

Question 9. Nylon-2-Nylon-6 is a biodegradable polymer obtained from glycine, \(\text{H}_2\text{N}-\text{CH}_2-\text{COOH}\) and aminocaproic acid, \(\text{H}_2\text{N}-(\text{CH}_2)_5-\text{COOH}\). Write the structure of this polymer.
Answer: The structure of Nylon-2-Nylon-6 is:
\(\left[ -\text{NH}-\text{CH}_2-\text{CO}-\text{NH}-(\text{CH}_2)_5-\text{CO}- \right]_n\)
In simple words: It is a copolymer of amino acid glycine and 6-aminohexanoic acid.

Exam Tip: Note that Nylon-2-Nylon-6 contains a 2-carbon unit from glycine and a 6-carbon unit from aminocaproic acid.

Question 10. Give two uses of teflon.
Answer:
1. Used in making non-stick frying pans.
2. Used in making oil seals, gaskets, and for insulating electrical wires.
In simple words: Teflon is used for non-stick cookware and electrical insulation.

Exam Tip: Teflon is chemically inert and thermally stable, which makes it ideal for non-stick coatings.

Question 11. Name the polymer used for making insulation material for coating copper wire. [Hint : PVC].
Answer: Polyvinyl chloride (PVC) is used for making insulation material for coating electrical copper wires.
In simple words: PVC is a tough plastic used to coat electrical wires.

Exam Tip: PVC stands for Polyvinyl chloride, formed by addition polymerization of vinyl chloride.

Question 12. Write the name and structure of monomer of the polymer which is used as synthetic wool.
Answer: The polymer used as synthetic wool is polyacrylonitrile (PAN) or Orlon. Its monomer is acrylonitrile, whose structure is:
\(\text{CH}_2=\text{CH}-\text{CN}\)
In simple words: Acrylonitrile is polymerized to make synthetic wool (Orlon).

Exam Tip: Do not confuse synthetic wool (PAN/Orlon) with synthetic silk (Nylon).

Question 13. How is vulcanized rubber obtained?
Answer: Vulcanized rubber is obtained by heating natural rubber with sulfur at an elevated temperature (373 K to 415 K) along with an additive like zinc oxide. This introduces sulfur cross-links between the polyisoprene chains.
In simple words: Heating raw rubber with sulfur makes it hard, strong, and elastic.

Exam Tip: Cross-linking restricts the independent movement of chains, improving elasticity and tensile strength.

Question 14. Name the polymer used for making radio television cabinets and feeding bottles of children.
Answer: Polystyrene is used for making radio and television cabinets, and polythene or polycarbonate is commonly used for feeding bottles.
In simple words: Polystyrene is rigid and moldable, making it suitable for appliance housings.

Exam Tip: Memorize common household applications of addition polymers like polystyrene and PVC.

Question 15. What do the digits 6 and 66 represent in the names nylon-6 and nylon-66?
Answer: The digit 6 in Nylon-6 represents the number of carbon atoms present in its single monomer (caprolactam). In Nylon-66, the first 6 represents the number of carbon atoms in hexamethylenediamine, and the second 6 represents the number of carbon atoms in adipic acid.
In simple words: The numbers tell us how many carbon atoms are present in the monomer molecules.

Exam Tip: This is a frequently asked board exam question. Make sure to distinguish between homopolymer numbering and copolymer numbering.

Question 16. Write the full form of PHBV.
Answer: Poly \(\beta\)-hydroxybutyrate-co-\(\beta\)-hydroxyvalerate.
In simple words: PHBV is a biodegradable copolymer used for specialized medical and packaging applications.

Exam Tip: Spell out the full form carefully without spelling errors to secure full marks.

Question 17. Which of the following sets has all polymers capable of repeatedly softening on heating and hardening on cooling?
(i) Glyptal, Melamine, PAN.
(ii) PVC, Polystyrene, polythene.
(iii) Polypropylene, urea formaldehyde resin, teflon.
Answer: (ii) PVC, Polystyrene, polythene.
Explanation: All three are thermoplastic polymers which soften on heating and harden on cooling. Melamine and urea-formaldehyde resins are thermosetting plastics.
In simple words: Thermoplastics can be reheated and reshaped, unlike thermosetting resins.

Exam Tip: Thermoplastics are generally linear or slightly branched polymers, whereas thermosets are heavily cross-linked.

Question 18. Why benzoyl peroxide is used as an initiator for chain growth polymerisation?
Answer: Benzoyl peroxide is used as an initiator because it undergoes homolytic cleavage upon heating to easily generate phenyl free radicals, which initiate the chain growth polymerization of alkenes.
In simple words: It breaks down easily into free radicals to kickstart the polymerization chain reaction.

Exam Tip: Free radical mechanism involves three steps: chain initiation, chain propagation, and chain termination.

SA (I) TYPE QUESTIONS (2 - MARK QUESTIONS)

Question 1. Give the structure of monomer of neoprene. What is the advantage of neoprene over the natural rubber?
Answer: The monomer of neoprene is chloroprene (2-chlorobut-1,3-diene). Its structure is:
\(\text{CH}_2=\text{C}(\text{Cl})-\text{CH}=\text{CH}_2\)
Advantage: Neoprene is superior to natural rubber because it has high resistance to vegetable and mineral oils, gasoline, and aging caused by air or heat.
In simple words: Neoprene is a synthetic rubber that resists oils and chemicals better than natural rubber.

Exam Tip: Mention chemical resistance to oils and solvents as the primary advantage of synthetic rubbers like neoprene and Buna-N over natural rubber.

Question 2. Classify the following as homopolymer or copolymer. Also classify them as addition or condensation polymers.

(i) \(\ce{-(NH-CH(R)-CO)_{n}-}\)

(ii) \(\ce{-(CH2-CH=CH-CH2-CH(C2H5))_{n}-}\)
Answer:
(i) Homopolymer and condensation polymer (Polypeptide / Protein type).
(ii) Copolymer and addition polymer.
In simple words: The first is formed from a single amino acid derivative by condensation, while the second is formed by adding two different unsaturated units.

Exam Tip: Look at the backbone structure: peptide/amide linkages indicate condensation, while carbon-carbon single chain backbones with double bonds or side alkyl groups typically indicate addition copolymers.

Question 3. Give the mechanism of polymerisation of ethene to polythene in presence of benzoyl peroxide.
Answer: The mechanism proceeds via a free radical chain mechanism in three steps:
1. Chain Initiation:
\((\text{C}_6\text{H}_5\text{COO})_2 \rightarrow 2\text{C}_6\text{H}_5^\bullet + 2\text{CO}_2\)
\(\text{C}_6\text{H}_5^\bullet + \text{CH}_2=\text{CH}_2 \rightarrow \text{C}_6\text{H}_5-\text{CH}_2-\text{CH}_2^\bullet\)
2. Chain Propagation:
\(\text{C}_6\text{H}_5-(\text{CH}_2-\text{CH}_2)_n-\text{CH}_2-\text{CH}_2^\bullet + \text{CH}_2=\text{CH}_2 \rightarrow \text{C}_6\text{H}_5-(\text{CH}_2-\text{CH}_2)_{n+1}-\text{CH}_2-\text{CH}_2^\bullet\)
3. Chain Termination:
Two radical chains combine to form a neutral dead polymer molecule.
In simple words: Free radicals attack ethene molecules successively to form long polymer chains until two radicals combine to stop the reaction.

Exam Tip: Clearly write out initiation, propagation, and termination steps with radical dots (\(^\bullet\)) for full marks.

Question 4. Complete the following reactions :
\(n(\text{CH}_2=\text{CH}_2) \xrightarrow[350-570\text{ K}, 1000-2000\text{ atm}]{\text{traces of peroxide}} \text{ ?}\)
\(n(\text{CH}_2=\text{CH}_2) \xrightarrow[333-343\text{ K}, 6-7\text{ atm}]{\text{Ziegler-Natta Catalyst}} \text{ ?}\)}
Answer:
1. \(n(\text{CH}_2=\text{CH}_2) \xrightarrow[350-570\text{ K}, 1000-2000\text{ atm}]{\text{traces of peroxide}} \left[ -\text{CH}_2-\text{CH}_2- \right]_n\) (Low density polythene - LDP)
2. \(n(\text{CH}_2=\text{CH}_2) \xrightarrow[333-343\text{ K}, 6-7\text{ atm}]{\text{Ziegler-Natta Catalyst}} \left[ -\text{CH}_2-\text{CH}_2- \right]_n\) (High density polythene - HDP)
In simple words: Ethene polymerizes to form polythene under different conditions of temperature, pressure, and catalyst.

Exam Tip: Peroxide initiator at high pressure gives LDP, whereas Ziegler-Natta catalyst at low pressure gives HDP.

Question 5. (i) What is the difference between step growth polymer and chain growth polymer?
(ii) Give one example of each type.
Answer:
(i) Chain growth polymers are formed by successive addition of monomer units to a reactive active center (free radical or ion) without loss of small molecules, whereas step growth polymers are formed by stepwise intermolecular condensation reactions, usually accompanied by the elimination of small molecules like \(\text{H}_2\text{O}\) or \(\text{HCl}\).
(ii) Example of chain growth polymer: Polythene. Example of step growth polymer: Nylon-6,6.
In simple words: Chain growth adds monomers one by one rapidly via active species, while step growth links molecules stepwise with the removal of simple by-products.

Exam Tip: Chain growth is generally addition polymerization; step growth is generally condensation polymerization.

Question 6. How can you differentiate between thermosetting and thermoplastic polymers.
Answer:
1. Thermoplastics soften on heating and harden on cooling repeatedly, whereas thermosetting polymers become infusible and hard on heating and cannot be remolded.
2. Thermoplastics have linear or slightly branched chain structures with weak intermolecular forces, while thermosets have cross-linked 3D network structures.
In simple words: Thermoplastics can be recycled by melting, but thermosetting plastics cannot be melted once set.

Exam Tip: Contrast their behavior on heating and their underlying molecular architecture (linear vs. cross-linked).

Question 7. Mention the type of intermolecular forces present in nylon-6,6. What properties do they impart to nylon?
[Hint : Strong intermolecular forces of attraction like Hydrogen bonding. This results in close packing of chains and thus impart crystalline nature to the fibres.]
Answer: Nylon-6,6 molecules are held together by strong intermolecular hydrogen bonding between adjacent amide (\(-\text{CO}-\text{NH}-\)) groups. This strong hydrogen bonding leads to close packing of polymer chains, imparting high tensile strength, high crystallinity, and fiber-like properties.
In simple words: Hydrogen bonds hold the chains tightly together, making nylon exceptionally strong and tough.

Exam Tip: Whenever asked about polyamide properties, explicitly mention hydrogen bonding and crystalline nature.

Question 8. What is the difference between linear chain and branched chain polymers. Explain giving examples.
Answer: Linear polymers consist of long, straight, and continuous chains of monomer units that pack closely together, giving high density and tensile strength (e.g., High Density Polythene - HDP). Branched chain polymers contain linear chains having side chains or branches of various lengths, which prevent close packing, resulting in lower density and lower melting points (e.g., Low Density Polythene - LDP).
In simple words: Linear chains fit closely together making dense materials, while branched chains are loosely packed.

Exam Tip: High density polythene is linear; low density polythene is branched.

Question 9. Identify the polymer whose structure are given and mention one of their important use.
(i) \( -\left[ \text{CO}-(\text{CH}_2)_5-\text{NH} \right]_n-
(ii) \(-\left[ \text{CH}_2-\text{CHCl} \right]_n-\)
Answer:
(i) Polymer: Nylon-6. Important use: Used in the manufacture of tire cords, fabrics, and ropes.
(ii) Polymer: Polyvinyl chloride (PVC). Important use: Used for making water pipes, raincoats, and vinyl flooring.
In simple words: (i) is Nylon-6 for textiles, and (ii) is PVC for pipes and insulation.

Question 10. Arrange the following polymers in the order of increasing intermolecular forces :
(i) Nylon-6,6, Buna-S, Polythene.
(ii) Nylon-6, Neoprene, Polyvinylchloride
Answer:
(i) Buna-S < Polythene < Nylon-6,6 (Elastomer < Thermoplastic < Fibre)
(ii) Neoprene < Polyvinylchloride < Nylon-6 (Elastomer < Thermoplastic < Fibre)
In simple words: Elastomers have the weakest forces, thermoplastics are intermediate, and fibers (polyamides) have the strongest forces.

Exam Tip: General rule for intermolecular forces: Elastomers < Thermoplastics < Fibres.

Question 11. Write the expanded form and give the structures of monomers for the following polymers:
(i) PAN (ii) PTFE
Answer:
(i) PAN: Polyacrylonitrile. Monomer structure: \(\text{CH}_2=\text{CH}-\text{CN}\) (Acrylonitrile)
(ii) PTFE: Polytetrafluoroethylene (Teflon). Monomer structure: \(\text{CF}_2=\text{CF}_2\) (Tetrafluoroethylene)
In simple words: PAN is made from acrylonitrile and PTFE is made from tetrafluoroethylene.

Question 12. Novolac is the linear polymer which on heating with formaldehyde forms cross-linked bakelite. Write the structures of monomers and the polymer novolac.
Answer:
Monomers:
1. Phenol: \(\text{C}_6\text{H}_5\text{OH}\)
2. Formaldehyde: \(\text{HCHO}\)
Structure of Novolac: A linear chain of phenol rings connected via \(-\text{CH}_2-\) methylene bridges at ortho or para positions: \(\left[ -\text{C}_6\text{H}_2(\text{OH})-\text{CH}_2- \right]_n\)
In simple words: Novolac is a linear precursor of bakelite formed by condensing phenol with formaldehyde.

Exam Tip: Novolac is linear; reaction with more formaldehyde turns it into cross-linked bakelite.

Question 13. Write the structure of following polymers and also give their main uses :
(a) Polystyrene (ii) Melamine - formaldehyde resin.
Answer:
(a) Polystyrene structure: \(\left[ -\text{CH}_2-\text{CH}(\text{C}_6\text{H}_5)- \right]_n\). Use: Making insulation, toys, and packaging.
(ii) Melamine-formaldehyde resin structure: Highly cross-linked network of melamine and formaldehyde units. Use: Making unbreakable crockery and tableware.
In simple words: Polystyrene is used for packing and toys, while melamine resin is used for making hard dinnerware.

Exam Tip: Melamine crockery is thermosetting and does not break easily upon dropping.

Question 14. Identify the polymers used in the manufacture of paints and lacquers. Write the structure of the polymer and its monomers.
Answer: Glyptal is used in the manufacture of paints and lacquers.
Monomers: Ethylene glycol (\(\text{HO}-\text{CH}_2-\text{CH}_2-\text{OH}\)) and Phthalic acid (\(\text{C}_6\text{H}_4(\text{COOH})_2\)).
Structure of Glyptal: \(\left[ -\text{O}-\text{CH}_2-\text{CH}_2-\text{O}-\text{CO}-\text{C}_6\text{H}_4-\text{CO}- \right]_n\)
In simple words: Glyptal is a polyester used in paints and lacquers.

Exam Tip: Glyptal is a polyester formed by condensation of ethylene glycol and phthalic acid.

Question 15. Can a copolymer be formed by both addition and condensation polymerisation? Explain with the help of examples.
Answer: Yes, copolymers can be formed by both addition and condensation polymerizations.
- Addition copolymerization example: Buna-S is formed by the addition copolymerization of 1,3-butadiene and styrene.
- Condensation copolymerization example: Nylon-6,6 is formed by the condensation copolymerization of hexamethylenediamine and adipic acid.
In simple words: Copolymers simply mean two different monomers are used, which can happen via either addition or condensation reactions.

Exam Tip: Do not confuse copolymerization (different monomers) with condensation (elimination of small molecules).

Question 16. What is the difference between an elastomer and a fibre? Give one example of each.
Answer: Elastomers are rubber-like solids with weak intermolecular forces that allow them to be stretched under stress and spring back into shape (e.g., Buna-S). Fibres are thread-forming solids with high tensile strength and strong intermolecular forces like hydrogen bonding that prevent stretching (e.g., Nylon-6,6).
In simple words: Elastomers stretch easily, while fibres are strong and rigid.

Question 17. Write the structure of the monomers used in the synthesis of :
(i) Nylon-6 (ii) Nylon-6, 6
Answer:
(i) Monomer of Nylon-6: Caprolactam, structure is a 7-membered cyclic lactam ring containing a \(-\text{NH}-\text{CO}-\) group and 5 methylene units: \(\text{HN}-(\text{CH}_2)_5-\text{CO}\)
(ii) Monomers of Nylon-6,6:
- Hexamethylenediamine: \(\text{H}_2\text{N}-(\text{CH}_2)_6-\text{NH}_2\)
- Adipic acid: \(\text{HOOC}-(\text{CH}_2)_4-\text{COOH}\)
In simple words: Nylon-6 uses caprolactam, while Nylon-6,6 uses a diamine and a diacid.

Exam Tip: Draw cyclic caprolactam correctly for Nylon-6.

SA (II) TYPE QUESTIONS (3 - MARK QUESTIONS)

Question 1. Differentiate between the following pairs :
(i) Branched chain polymers and cross linked polymers.
(ii) Thermoplastic and thermosetting polymers.
(iii) Chain growth and step growth polymerisation.
Answer:
(i) Branched chain polymers consist of linear chains having side branches, resulting in lower density and melting point (e.g., LDP). Cross-linked polymers have strong covalent bonds linking linear chains together to form a rigid 3D network (e.g., Bakelite).
(ii) Thermoplastics soften on heating and can be repeatedly remolded (e.g., PVC). Thermosetting polymers undergo cross-linking on heating to become permanently hard and infusible (e.g., Melamine resin).
(iii) Chain growth polymerization occurs via addition of monomers to reactive intermediates without losing small molecules, proceeding rapidly. Step growth polymerization occurs by stepwise condensation of bi-functional or poly-functional monomers with the elimination of small molecules like \(\text{H}_2\text{O}\).
In simple words: These polymer pairs differ in their molecular architecture, thermal behavior, and reaction mechanism.

Exam Tip: Use comparative tables or clear bullet points for differentiating questions to score full marks.

Question 2. List two uses each of the following polymers :
(i) Nylon-2-Nylon-6. (ii) Urea-formaldehyde resin (iii) Glyptal
Answer:
(i) Nylon-2-Nylon-6: Used as a biodegradable surgical suture and in biomedical packaging.
(ii) Urea-formaldehyde resin: Used for making unbreakable cups, saucers, and adhesive for wood laminates.
(iii) Glyptal: Used in the manufacture of paints, lacquers, and electrical insulation varnishes.
In simple words: Each of these polymers has specific industrial and domestic applications based on their properties.

Exam Tip: Memorize two distinct uses for each named polymer in the NCERT syllabus.

Question 3. (i) What is meant by biodegradable polymers?
(ii) A biodegradable polymer is used in speciality packaging, orthopaedic devices and in controlled release of drugs. Identify the polymer and give its structure.
Answer:
(i) Biodegradable polymers are polymers that undergo decomposition by bacterial action or enzymatic processes in the environment into natural products like \(\text{CO}_2\) and \(\text{H}_2\text{O}\).
(ii) The polymer is PHBV (Poly \(\beta\)-hydroxybutyrate-co -\(\beta\)-hydroxyvalerate). Its structure is:
\(\left[ -\text{O}-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CO}-\text{O}-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CO}- \right]_n\)
In simple words: Biodegradable polymers break down naturally, and PHBV is used for medical devices and controlled drug delivery.

Exam Tip: PHBV stands for Poly \(\beta\)-hydroxybutyrate-co-\(\beta\)-hydroxyvalerate, an eco-friendly copolymer.

Question 4. Write the name and formula of the following polymers.
(a) Nylon 5, 6 (b) Nylon 6
(c) PHBV (d) Terylene
(e) Buna-S (f) Bakelite
Answer:
(a) Nylon 5,6: Name: Polyhexamethylenepentanamide (or copolymer of pentanedioic acid and hexamethylenediamine). Formula: \(\left[ -\text{CO}-(\text{CH}_2)_3-\text{CO}-\text{NH}-(\text{CH}_2)_6-\text{NH}- \right]_n\)
(b) Nylon 6: Name: Polycaprolactam. Formula: \(\left[ -\text{CO}-(\text{CH}_2)_5-\text{NH}- \right]_n\)
(c) PHBV: Name: Poly \(\beta\)-hydroxybutyrate-co-\(\beta\)-hydroxyvalerate. Formula: \(\left[ -\text{O}-\text{CH}(\text{CH}_3)\text{CH}_2\text{CO}-\text{O}-\text{CH}(\text{C}_2\text{H}_5)\text{CH}_2\text{CO}- \right]_n\)
(d) Terylene (Dacron): Name: Polyethylene terephthalate. Formula: \(\left[ -\text{O}-\text{CH}_2-\text{CH}_2-\text{O}-\text{CO}-\text{C}_6\text{H}_4-\text{CO}- \right]_n\)
(e) Buna-S: Name: Butadiene-styrene copolymer. Formula: \(\left[ -\text{CH}_2-\text{CH}=\text{CH}-\text{CH}_2-\text{CH}(\text{C}_6\text{H}_5)-\text{CH}_2- \right]_n\)
(f) Bakelite: Name: Phenol-formaldehyde polymer. Formula: Cross-linked network of phenol rings bridged by \(-\text{CH}_2-\) groups.
In simple words: These formulas represent the repeating structural units of important commercial polymers.

Exam Tip: Practice writing polymer formulas by identifying repeating monomer units and removing small molecules where condensation occurs.