- polymers for class 12 Notes
- NCERT Solutions For Class 12 Chemistry Chapter 15 Polymers
- Important Questions for CBSE Class 12 Chemistry – Polymers
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polymers for class 12 Notes
- The word ‘polymer’ is coined from two Greek words: poly means many and mer means unit or part.
- Plastics or polymers are integral part of our daily life.
- Polymers have huge applications everywhere.
- For example: – Hot water bag, tooth brush, switches, ropes etc. are all made of polymers.
Define the terms: Monomers, Polymers & Polymerization
- The term polymer is defined as a chemical substance of a very high molecular mass (103-107u) formed by combination of a simple molecule, called monomers.
- Polymers are also known as macromolecules, which are formed by repeating structural units on large scale.
- This process of formation of polymers from respective monomers is called polymerisation.
- For example:- n CH2 = nCH2–> n[-CH2-CH2-] –> [-CH2-CH2-] n
Ethene Repeating Unit Polythene polymer
Classification of Polymers
There are several ways of classification of polymers based on some special considerations.
The following are some of the common classifications of polymers:
- Mode of polymerization
- Molecular Force
- Under this type of classification, there are three sub categories.
- Natural polymers
- These polymers are found in plants and animals. Examples are proteins, cellulose, starch, some resins and rubber.
- Natural polymers
- Semi-synthetic polymers
- b) Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the some examples.
- Synthetic Polymers
- A variety of synthetic polymers as plastic (polythene), synthetic fibres. Examples: – (nylon 6, 6) and synthetic rubbers (Buna – S) are polymers extensively used in daily life as well as in industry.
- There are three different types based on the structure of the polymers.
Polymers can also be classified on the basis of mode of polymerisation into two sub groups.
- Addition polymers: –
- The addition polymers are formed by the repeated addition of monomer molecules possessing double or triple bonds.
- For example: – The formation of polythene from Ethene and polypropene from propene.
- However, the addition polymers formed by the polymerisation of a single monomeric species are known as homopolymers.
- For example: – polythene.
n CH2=CH2 –> (CH2-CH2-)n Homopolymer
- The polymers made by addition polymerisation from two different monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc.
nCH2 = CH- CH =CH2 + n C6H5CH=CH2 à (-CH2-CH=CH-C6H5-CH2-CH-CH2-) n
1,3 – Butadiene Styrene Butadiene-styrene copolymer
- Condensation polymers
- The condensation polymers are formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units.
- In these polymerisation reactions, the elimination of small molecules such as water, alcohol, hydrogen chloride, etc. take place.
- The examples are Terylene (Dacron), nylon 6, 6, nylon 6, etc.
- For example, nylon 6, 6 is formed by the condensation of hexamethylene diamine with adipic acid.
- A large number of polymers can be used in different fields because of their mechanical properties like tensile strength, elasticity, toughness etc.
- These mechanical properties are governed by intermolecular forces, e.g., van der Waals forces and hydrogen bonds, present in the polymer. These forces also bind the polymer chains.
- The polymers are classified into the following four sub groups on the basis of magnitude of intermolecular forces present in them.
- a) Elastomers: –
- These are rubber – like solids with elastic properties.
- The polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched.
- A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber. The examples are Buna-S, Buna-N, neoprene, etc.
- b) Fibres:-
- Fibres are the thread forming solids which possess high tensile strength and high modulus.
- These characteristics can be attributed to the strong intermolecular forces like hydrogen bonding.
- These strong forces also lead to close packing of chains and thus impart crystalline nature. The examples are polyamides (nylon 6, 6), polyesters (terylene), etc.
- c) Thermoplastic Polymers:-
- These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling.
- These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres.
- Some common thermoplastics are polythene, polystyrene, polyvinyl, etc.
- d) Thermosetting Polymers:-
- These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible.
- These cannot be reused. Some common examples are Bakelite, urea-formaldehyde resins, etc.
Types of Polymerization Reactions
- There are broadly 2 types of polymerization reactions:-
- Addition or chain growth polymerization
- Condensation or step growth polymerization
Addition or chain growth polymerization
- The molecules of the same monomer or different monomers add together on a large scale to form a polymer.
- The monomers used are unsaturated compounds, e.g., alkenes, alkadienes and their derivatives.
- This mode of polymerisation leading to an increase in chain length or chain growth can take place through the formation of either free radicals or ionic species.
- However, the free radical governed addition or chain growth polymerisation is the most common mode.
- Free Radical Mechanism:-
- Many of alkenes or dienes and their derivatives are polymerized in the presence of a free radical (catalyst) like benzoyl peroxide.
- The sequence of steps may be depicted as follows:
- Chain initiation steps
- Chain propagating step
- Chain terminating step
- The polymerisation of Ethene to polythene consists of heating or exposing to light a mixture of Ethene with a small amount of benzoyl peroxide initiator.
- The process starts with the addition of phenyl free radical formed by the peroxide to the Ethene double bond thus generating a new and larger free radical. This step is called chain initiating step.
- Ultimately, at some stage the product radical thus formed reacts with another radical to form the polymerised product. This step is called the chain terminating step.
Chain terminating step
Preparation of Important Addition Reaction
Polythene: – There are two types of polythene-
- Low density polythene:
- It is obtained by the polymerisation of Ethene under high pressure of 1000 to 2000 atmospheres at a temperature of 350 K to 570 K in the presence of traces of dioxygen or a peroxide initiator (catalyst).
- The low density polythene (LDP) obtained through the free radical addition and H-atom abstraction has highly branched structure.
- Low density polythene is chemically inert and tough but flexible and a poor conductor of electricity.
- Hence, it is used in the insulation of electricity carrying wires and manufacture of squeeze bottles, toys and flexible pipes.
- High density polythene:
- It is formed when addition polymerisation of Ethene takes place in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler-Natta catalyst) at a temperature of 333 K to 343 K and under a pressure of 6-7 atmospheres.
- High density polythene (HDP) thus produced, consists of linear molecules and has a high density due to close packing.
- It is also chemically inert and more tough and hard. It is used for manufacturing buckets, dustbins, bottles, pipes, etc.
- Polytetrafluroethene (Teflon)
- Teflon is manufactured by heating tetrafluoroethene with a free radical or per sulphate catalyst at high pressures.
- It is chemically inert and resistant to attack by corrosive reagents. It is used in making oil seals and gaskets and also used for non – stick surface coated utensils.
- The addition polymerisation of acrylonitrile in presence of a peroxide catalyst leads to the formation of polyacrylonitrile.
- Polyacrylonitrile is used as a substitute for wool in making commercial fibres as Orlon or acrilan.
Condensation Polymerization or step growth polymerization
- This type of polymerisation involves a repetitive condensation reaction between two bi-functional monomers.
- These poly condensation reactions results in the loss of some simple molecules as water, alcohol, etc., and lead to the formation of high molecular mass condensation polymers.
- In these reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on.
- Since, each step produces a distinct functionalised species and is independent of each other; this process is also called as step growth polymerisation.
- The formation of Terylene or Dacron by the interaction of ethylene glycol and terephthalic acid is an example of this type of polymerisation.
Preparation of Important Addition Reaction
- These polymers possessing amide linkages are important examples of synthetic fibres and are termed as nylons. The general method of preparation consists of the condensation polymerisation of diamines with dicarboxylic acids and also of amino acids and their lactams.
- Preparation of Nylons
- Nylon 6, 6:-
- It is prepared by the condensation polymerisation of hexamethylenediamine with adipic acid under high pressure and at high temperature.
- Nylon 6, 6 is used in making sheets, bristles for brushes and in textile industry.
- Nylon 6, 6:-
- Copolymerisation is a polymerisation reaction in which a mixture of more than one monomeric species is allowed to polymerise and form a copolymer.
- The copolymer can be made not only by chain growth polymerisation but by step growth polymerisation also.
- It contains multiple units of each monomer used in the same polymeric chain.
- For example:-a mixture of 1, 3 – butadiene and styrene can form a copolymer.
- Copolymers have properties quite different from homopolymers.
- For example: – butadiene – styrene copolymer is quite tough and is a good substitute for natural rubber.
- It is used for the manufacture of auto tyres, floor tiles, footwear components, cable insulation, etc.
- Rubber is a natural polymer and possesses elastic properties.
- It is also termed as elastomer and has a variety of uses.
- It is manufactured from rubber latex which is a colloidal dispersion of rubber in water. This latex is obtained from the bark of rubber tree and is found in India, Sri Lanka, Indonesia, Malaysia and South America.
- Natural Rubber
- Natural rubber may be considered as a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis – 1, 4 -polyisoprene.
- The cis-polyisoprene molecule consists of various chains held together by weak van der Waals interactions and has a coiled structure.
- Thus, it can be stretched like a spring and exhibits elastic properties.
Vulcanization of Rubber:-
- Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 K) and shows high water absorption capacity.
- It is soluble in non-polar solvents and is non-resistant to attack by oxidising agents. To improve upon these physical properties, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range 373 K to 415K.
- On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.
- In the manufacture of tyre rubber, 5% of sulphur is used as a crosslinking agent.
- The probable structures of vulcanised rubber molecules are depicted below:
- Synthetic Rubber
- Synthetic rubber is any vulcanisable rubber like polymer, which is capable of getting stretched to twice its length.
- However, it returns to its original shape and size as soon as the external stretching force is released.
- Thus, synthetic rubbers are either homopolymers of 1, 3 – butadiene derivatives or copolymers of 1, 3 – butadiene or its derivatives with another unsaturated monomer.
Preparation of Synthetic Rubbers
- Neoprene or poly chloroprene is formed by the free radical polymerisation of chloroprene.
- It has superior resistance to vegetable and mineral oils.
- It is used for manufacturing conveyor belts, gaskets and hoses.
- A large number of polymers are quite resistant to the environmental degradation processes and are thus responsible for the accumulation of polymeric solid waste materials.
- Aliphatic polyesters are one of the important classes of biodegradable polymers.
- Some important examples are given below:
- Poly β-hydroxybutyrate – co-β-hydroxy valerate (PHBV)
- It is obtained by the copolymerisation of 3-hydroxybutanoic acid and
3 – Hydroxypentanoic acid.
- PHBV is used in speciality packaging, orthopaedic devices and in controlled release of drugs. PHBV undergoes bacterial degradation in the environment.
NCERT Solutions For Class 12 Chemistry Chapter 15 Polymers
NCERT INTEXT QUESTIONS ( polymers for class 12 Notes )
15.1. What are polymers?
Ans: Polymers are high molecular mass substances (103 — 107u) consisting of a very large number of simple repeating structural units joined together through covalent bonds in a linear fashion. They are also called macromolecules. Ex: polythene, nylon 6,6, bakelite, rubber, etc.
15.2. How are polymers classified on the basis of structure?
Ans: On the basis of structure, polymers are classified into three types. These are linear chain polymers, branched chain polymers and crossedlinkedpolymers.
1. Linear chain polymers: In this case, the monomer units are linked to one another to form long linear chains. These linear chains are placed one above the other and are closely packed in space. The close packing results in high densities, tensile strength and also high melting and boiling points. High density polyethene is a very common example of this type. Nylon, polyesters and PVC are also linear chain polymers.
2. Branched chain polymers: In this type of polymers, the monomer units are linked to form long chains which have also side chains or branched chains of different Lengths attached to them. As a result of branching, these polymers are not closely packed in space. They have low densities, low tensile strength as well as low melting and boiling points. Some common examples of such polymers are ; low density polyethene, amylopectin, starch, glycogen etc.
3. Cross: linked polymers. In these polymers, also called net—work polymers, the monomer units are linked together to form three dimensionaL net—work as shown in the figure. These are expected to be quite hard, rigid and brittle. Examples of cross linked polymers are bakelite, glyptal. melamine formaldehyde polymer etc.
15.3. Write the names of the monomers of the following polymers:
Ans: (i) Hexamethylene diamine NH2-(CH2)6NH2 and adipic acid HOOC – (CH2)4 – COOH
(iii) Tetrafluoroethene F2C = CF2
15.4. Classify the following as addition and condensation polymers:
Terylene, Bakelite, Polyvinyl chloride,Polythene
Ans: Addition polymers: Polyvinyl chloride, Polythene
Condensation polymers : Terylene, bakelite.
15.5. Explain the difference between Buna-N and Buna-S.
Ans: Both Buna-N and Buna-S are synthetic rubber and are co-polymers in nature. They differ in their constituents.
Buna-N: Constituents are : buta-1, 3-diene and acrylonitrile.
Buna-S: Constituents are : buta-1, 3-diene, and styrene. They condense in the presence of Na.
Buna – S: It is a co—polymer of 1. 3 – butadiene and styrene and is prepared by the polymerisation of these components in the
ratio of 3 : 1 in the presence of sodium.
15.6. Arrange the following polymers in increasing order of their intermolecuiar forces.
(i) Nylon 6,6, Buna-S, Polythene
(ii) Nylon 6, Neoprene, Polyvinyl chloride
Ans: On the basis of intermolecuiar forces, polymers
are classified as elastomers, fibres and plastics. The increasing order of intermolecuiar forces is: Elastomer < Plastic < fibre.
Thus, we have
(i)Buns-S < Polythene < Nylon 6,6
(ii)Neoprene < Polyvinyl chloride < Nylon 6.
NCERT EXRECISES ( polymers for class 12 Notes )
15.1. Explain the terms polymer and monomer.
Ans: Polymers are high molecular mass substances consisting of a very large number of simple repeating structural units joined together through covalent bonds in a regular fashion. Polymers are also called macromolecules. Some examples are polythene, nylon-66, bakelite, rubber, etc. Monomers are the. simple and reactive molecules from which the polymers are prepared either by addition or condensation polymerisation. Some examples are ethene, vinyl chloride, acrylonitrile, phenol and formaldehyde etc.
15.2. What are natural and synthetic polymers ? Give two examples of each.
1. Natural polymers: The polymers which occur in nature mostly in plants and animals are called natural polymers. A few common examples are starch, cellulose, proteins, rubber nucleic acids, etc. Among them, starch and cellulose are the polymers of glucose molecules. Proteins are formed from amino acids which may be linked in different ways. These have been discussed in detail in unit 15 on biomolecules. Natural rubber is yet another useful polymer which is obtained from the latex of the rubber tree. The monomer units are of the unsaturated hydrocarbon 2-methyl-i, 3-butadiene, also called isoprene.
Example of natural polymers: Natural rubber, cellulose, nucleic acids, proteins etc.
2. Synthetic polymers: The polymers which are prepared in the laboraroiy are called synthetic polymers. These are also called man made polymers and have been developed in the present century to meet the ever increasing demand of the modem civilisation.
Example of synthetic polymers: Dacron (or terylene), Bakelite, PVC, Nylon-66, Nylon-6 etc.
15.3. Distinguish between the terms homopolymer and copolymer and give an example of each.
Ans: Polymers whose repeating structural units are derived from only one type of monomer units are called homopolymers, e.g., PVC polyethene, PAN, teflon, polystyrene, nylon- 6 etc.
Polymers whose repeating structural units are derived from two or more types of monomer molecules are copolymers, e.g., Buna-S, Buna-N, nylon-66, polyester, bakelite.
15.4. How do you explain the functionality of a monomer?
Ans: Functionality of a monomer implies the number of bonding sites present in it. For example, monomers like propene, styrene, acrylonitrile have functionality of one which means that have one bonding site.
Monomers such as ethylene glycol, hexamethylenediamine, adipic acid have functionality of two which means that they have two bonding sites.
15.5. Define the term polymerisation?
Ans: It is a process of formation of a high molecular Sol. mass polymer from one or more monomers by linking together a large number of repeating structural units through covalent bonds.
15.6. Is (-NH — CHR—CO-)n a homopolymer or copolymer?
Ans: It is a homopolymer because the repeating structural unit has only one type of monomer, i.e., NH2—CHR—COOH.
15.7. In which classes, are the polymers classified on the basis of molecular forces?
Ans: Polymers are classified into four classes on the basis of molecular forces. These are:
elastomers, fibres, thermoplastic polymers and thermosetting polymers.
1. Elastomers: In these polymers, the intermolecular forces are the weakest. As a result, they can be readily stretched by applying small stress and regain their original shape when the stress is removed. The elasticity can be further increased by introducing some cross – links in the polymer chains. Natural rubber is the most popular example of elastomers. A few more examples are of: buna-S, buna-N and neoprene.
2. Fibres: Fibres represent a class of polymers which are thread-like and can be woven into fabrics in a number of ways. These are widely used for making clothes, nets, ropes, gauzes etc. Fibres possess high tensile strength because the chains possess strong intermolecular forces such as hydrogen bonding. These forces are also responsible for close packing of the chains. As a result, the fibres are crystalline in nature and have aJso sharp melting points. A few common polymers belonging to this class are nylon – 66, terylene and polyacrylonitrile etc.
3. Thermoplastics: These are linear polymers and have weak van der Waals forces acting in the various chains and are intermediate of the forces present in the elastomers and in the fibres. When heated, they melt and form a fluid which sets into a hard mass on cooling, Thus, they can be cast into different shapes by using suitable moulds. A few common examples are polyethene and polystyrene polyvinyls etc. These can be used for making toys, buckets, telephone apparatus, television cabinets etc.
4. Thermosetting plastics: These are normally semifluid substances with low molecular masses. When heated, they become hard and infusible due to the cross-linking between the polymer chains. As a result, they also become three dimensional in nature. They do not melt when heated. A few common thermosetting polymers are bakelite, melamine-formaldehyde, urea-formaldehyde and polyurethane etc.
15.8. How can you differentiate between addition and condensation polymerisatiop?
Ans: In addition polymerization, the molecules of the same or different monomers simply add on to one another leading to the formation of a macromolecules without elimination of small molecules like H2O, NH3 etc. Addition polymerization generally occurs among molecules containing double and triple bonds. For example, formation of polythene from ethene and neoprene from chloroprene, etc. In condensation polymerisation, two or more bifunctional trifimctional molecules undergo a series of independent condensation reactions usually with the elimination of simple molecules like water, alcohol, ammonia, carbon dioxide and hydrogen chloride to form a macromolecule. For example, nylon-6,6 is a condensation polymer of hexamethylenediamine and adipic acid formed by elimination of water molecules.
15.9. Explain the term copolymerisation and give two examples.
Ans: When two or more different monomers are allowed to polymerise together the product formed is called a copolymer, and the process in called copolymerisation. Example, Buna-S and Buna-N. Buna- S is a copolymer of 1, 3- butadiene and styrene while Buna-N is a copolymer of 1,3-butadiene and acrylonitrile.
15.10. Write the free radical mechanism for the polymerisation of ethene.
15.11. Define thermoplastics and thermo setting polymers with two examples of each
Ans: Thermoplastics polymers are linear polymer which can be repeatedly melted and moulded again and again on heating without any change in chemical composition and mechanical strength. Examples are polythene and polypropylene.
Thermosetting polymers, on the other hand, are permanently setting polymers. Once on heating in a mould, they get hardened and set, and then cannot be softened again. This hardening on heating is due to cross- linking between different polymeric chains to give a three dimensional network solid. Examples are bakelite, melamine-foimaldehyde polymer etc.
15.12. Write the monomers used for gettingThe following polymers:
(ii) Teflon (iii) Bakelite
15.13. Write the name and structure of one of the common initiators used in free radical addition polymerisation.
15.14. How does the presence of double bonds in rubber molecules influence their structure and reactivity?
Ans: Natural rubber is cis-polyisoprene and is obtained by 1, 4-polymerization of isoprene units. In this polymer, double bonds are located between C2 and C3 of each isoprene unit. These cis-double bonds do not allow the polymer chains to come closer for effective interactions and hence intermolecular forces are quite weak. As a result, natural rubber, i.e., cis-polyisoprene has a randomly coiled structure not the linear one and hence show elasticity.
15.15. Discuss the main purpose of vulcanisation of rubber.
Ans: Natural rubber has the following disadvantages:
(a) It is soft and sticky and becomes even more so at high temperatures and brittle at low temperatures. Therefore, rubber is generally used in a narrow temperature range (283-335 K) where its elasticity is maintained.
(b)It has large water absorption capacity, has low tensile strength and low resistance to abrasion.
(c)It is not resistant to the action of organic solvents.
(d)It is easily attacked by oxygen and other oxidising agents. .
To improve all these properties, natural rubber is vulcanised by heating it with about 5% sulphur at 373-415 K. The vulcanized rubber thus obtained has excellent elasticity over a larger range of temperature, has low water absorption tendency and is resistant to the action of organic solvents and oxidising agents.
15.16. What are the monomeric repeating units of Nylon-6 and Nylon 6,6?
15.17. Write the names and structures of the monomers of the following polymers:
(i) Buna-S (ii) Buna-N (iii) Dacron (iv) Neoprene
15.18. Identify the monomer in the following polymeric structures:
15.19. How is dacron obtained from ethylene glycol and terephthalic acid?
Ans: Dacron is obtained by condensation polymerization of ethylene glycol and terephthalic acid with the elimination of water molecules. The reaction is carried out at 420 – 460 K in presence of a catalyst consisting of a mixture of zinc acetate and antimony trioxide.
15.20. What is a biodegradable polymer ? Give an example of a biodegradable aliphatic polyester.
Ans: Polymers which disintegrate by themselves over a period of time due to environment degradation by bacteria, etc., are called biodegradable polymers. Example is PHBV, i. e., Poly-β-Hydroxybutyrate-co-β- Hydroxyvalerate.
Important Questions for CBSE Class 12 Chemistry – Polymers
1 Mark Questions ( polymers for class 12 )
1. Name the two types of polymeristion.
Ans.The two types of polymerisation are
(a) Addition polymerisation and
(b) Condensation polymerisation.
2. Name some initiators.
Ans.Examples of initiator are –
Benzoyl peroxide, acetyl peroxide, tert – butyl peroxide etc.
3. Name the two type of polyethene.
Ans.Polyethene is of two types –
1) Low Density Polyethene 2) High Density Polythene
4. Write the monomer of Teflon.
Monomer = Tetrafluoroethene
5. Give preparation of polyacrylonitrile.
6. Write one use of each – Teflon and polyacrylonitrile.
(1) Teflon is used in making oil seals & for non – stick surface coated utensils.
(2) Polyacrytonitrile is used for wool in making commercial fibres an orlon or acrilan.
7. Classify the following substances as natural, semi – synthetic and synthetic polymer
Ans. Natural polymers: Cellulose, Starch, And Protein
Synthetic: Plastic, Nylon
8. Give two examples of each (i) linear polymer (ii) Network polymer.
Ans. Linear polymers: Polythene, Polyvinylchloride
Network polymers: Bakelite, Melamine
9. Why is condensation polymerisation also called on step – growth polymerisation?
Ans. Condensation polymerisation produces a distinct functionalized species and is independent of each other. Therefore it is also called step growth polymerisation.
10. Write some examples of condensation polymers.
Ans. Examples of condensation polymers are Nylon-6, 6, Dacron, Nylon 6 etc
11. How is Nylon – 6, 6 different from Nylon -6?
Ans. Nylon – 6, 6 is made of two bifunctional monomers, each having 6 carbon atoms whereas Nylon – 6 is made from heating only one monomer having 6 carbon atoms.
12. Give the formula of monomer of Nylon – 6.
Ans. Monomer of Nylon -6 is caprolactum
13. What is copolymerisation?
Ans. The reaction in which a mixture of more than one monomeric species is allowed to polymerise & form a copolymer is called copolymerisation e.g. Buna -S.
14. What is the monomer of natural rubber?
Ans. Monomer of national rubber is isoprene or 2 – methyl – 1, 3 – butadiene.
15. Give two examples of synthetic rubber.
Ans. Example of synthetic rubber – Neoprene, Buna – N etc.
16. Give one example of biodegradable polymer.
Ans. Biodegradable polymer: PHVB, Nylon – 2 – Nylon -6.
17. Classify following on Homopolymer and copolymer- PVC, Polystyrene, Buna – S, Neoprene, Buna – N, Teflon.
Ans. Homopolymer Copolymer
PVC Buna – S
Polystyrene Buna – N
18. Classify following an addition and condensation polymer- Bakelite, Polythene, Nylon – 6, 6, Polyacrylonitrile
Ans. Addition polymer condensation polymers
Polyacrylonitrite Nylon – 6, 6, Bakelite
19.Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.
Polyvinyl chloride, polythene
20. Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.
Ans. Addition polymers:
Polyvinyl chloride, polythene
21. Explain the difference between Buna-N and Buna-S.
Ans. Buna – N is a copolymer of 1, 3-butadiene and acrylonitrile.
Buna – S is a copolymer of 1, 3-butadiene and styrene.
22. Is , a homopolymer or copolymer?
Ans. is a homopolymer because it is obtained from a single monomer unit, – CHR – COOH.
2 Marks Questions
1. Define polymers.
Ans. Polymer are defined a very large molecules having high molecular mass which are formed by joining of repeating structural units on a large scale.
2. Write various uses of polymers.
Ans. Polymers are used in manufacture of plastic buckets, cups and saucers, children’s toys, packaging bags, synthetic clothing materials, automobile tyres, insulating materials etc. polymers are the back bone of five major industries – plastics, elastomers, fibres, paints & varnishes.
3. On what basis are polymers classified?
Ans. Polymers are classified on the basis of
c) Mode of polymerisation
(d) Molecular forces
4. What is the difference between a homopolymer and a copolymer?
|The addition polymers formed by polymerisation of a single monomeric species are known an homopolymers e.g. – polythene||The polymers made by addition polymerisation from two different monomers are known as copolymers e.g. Buna – S|
5. Explain the term vulcanisation of rubber?
Ans. To improve upon the physical properties of natural rubber a process of vulcanization is carried out. This process consist of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373K to 415K. On vulcanization, sulphur form cross links at the reactive sites of double bonds and thus the rubber get stiffened.
6. Write uses of bakelite and melamine.
Ans. Bakelite is used for making combs, phonograph records, electrical switches, handles. Melamine is used in manufacture of unbreakable crockery.
9. How are the characteristics of natural rubber modified?
Ans. Natural rubber is soft at high temperatures and brittle at low temperatures. It is soluble in non – polar solvents and non – resistant to oxidizing agents. These properties can be modified by mixing raw rubber with sulphur. & an appropriate additive at a temperature 373K to 415K. This is called venlcanisation.
10. What are polymers?
Ans.Polymers are high molecular mass macromolecules, which consist of repeating structural units derived from monomers. Polymers have a high molecular mass (103 – 107 u). In a polymer, various monomer units are joined by strong covalent bonds. These polymers can be natural as well as synthetic. Polythene, rubber, and nylon 6, 6 are examples of polymers.
11. What are natural and synthetic polymers? Give two examples of each type.
Ans.Natural polymers are polymers that are found in nature. They are formed by plants and animals. Examples include protein, cellulose, starch, etc.
Synthetic polymers are polymers made by human beings. Examples include plastic (polythene), synthetic fibres (nylon 6, 6), synthetic rubbers (Buna – S).
12. How do you explain the functionality of a monomer?
Ans.The functionality of a monomer is the number of binding sites that is/are present in that monomer.
For example, the functionality of monomers such as ethene and propene is one and that of 1, 3-butadiene and adipic acid is two.
13. Define the term polymerisation.
Ans.Polymerization is the process of forming high molecular mass (103 – 107 u) macromolecules, which consist of repeating structural units derived from monomers. In a polymer, various monomer units are joined by strong covalent bonds.
14. In which classes, the polymers are classified on the basis of molecular forces?
Ans.On the basis of magnitude of intermolecular forces present in polymers, they are classified into the following groups:
(iii) Thermoplastic polymers
(iv) Thermosetting polymers
15. Write the free radical mechanism for the polymerisation of ethene.
Ans. Polymerization of ethene to polythene consists of heating or exposing to light a mixture of ethene with a small amount of benzoyl peroxide as the initiator.
The reaction involved in this process is given below:
16. Write the name and structure of one of the common initiators used in free
radical addition polymerisation.
Ans. One common initiator used in free radical addition polymerization is benzoyl peroxide. Its structure is given below.
3 Marks Questions ( polymers for class 12 )
1. How are addition polymers different from condensation polymers?
Ans.Addition Polymers: – They are formed by the repeated addition of monomer molecules possessing double or triple bonds e.g. polythene
2. What is the basic difference between following pairs:
(a) Elastomers and fibres
(b) Thermo setting polymer & thermo plastic polymers.
|1. These are rubber like solids with elastic properties2. The polymer chains are held together by weakest intermolecular forces e.g. Buna – S||1. There are thread forming solids with high tensile strength2. The polymer chains are closely packed due to strong intermolecular forces like Hydrogen bond e.g. Nylon – 6, 6|
|1. They are linear or slightly branched molecules.2. They are capable of repeatedly softening on heating and hardening on cooling e.g. PVC.||1. They are cross – linked or heavily branched molecules.2. They undergo extensive cross linking on heating & can not be reversed e.g. bakelite.|
3. How are neoprene & Buna – N prepared? Which one is a copolymer?
Ans. Preparation of Neoprene-
4. Write the names of monomers of the following polymers:
5. Arrange the following polymers in increasing order of their intermolecular forces.
(i) Nylon 6, 6, Buna-S, Polythene.
(ii) Nylon 6, Neoprene, Polyvinyl chloride.
Ans.Different types of polymers have different intermolecular forces of attraction. Elastomers or rubbers have the weakest while fibres have the strongest intermolecular forces of attraction. Plastics have intermediate intermolecular forces of attraction. Hence, the increasing order of the intermolecular forces of the given polymers is as follows:
(i) Buna – S < polythene < Nylon 6, 6
(ii) Neoprene < polyvinyl chloride < Nylon 6
6. Explain the terms polymer and monomer.
Ans.Polymers are high molecular mass macromolecules composed of repeating structural units derived from monomers. Polymers have a high molecular mass (103 – 107 u). In a polymer, various monomer units are joined by strong covalent bonds. Polymers can be natural as well as synthetic. Polythene, rubber, and nylon 6, 6 are examples of polymers.
Monomers are simple, reactive molecules that combine with each other in large numbers through covalent bonds to give rise to polymers. For example, ethene, propene, styrene, vinyl chloride.
7. Define thermoplastics and thermosetting polymers with two examples of each.
Ans.Thermoplastic polymers are linear (slightly branched) long chain polymers, which can be repeatedly softened and hardened on heating. Hence, they can be modified again and again. Examples include polythene, polystyrene.
Thermosetting polymers are cross-linked or heavily branched polymers which get hardened during the molding process. These plastics cannot be softened again on heating. Examples of thermosetting plastics include bakelite, urea-formaldehyde resins.
8. How does the presence of double bonds in rubber molecules influence their structure and reactivity?
Ans.Natural rubber is a linear cis-polyisoprene in which the double bonds are present between of the isoprene units.
Because of this cis-configuration, intermolecular interactions between the various strands of isoprene are quite weak. As a result, various strands in natural rubber are arranged randomly. Hence, it shows elasticity.
10. What is a biodegradable polymer? Give an example of a biodegradable aliphatic polyester.
Ans.A polymer that can be decomposed by bacteria is called a biodegradable polymer.
Poly--hydroxybutyrate-CO-– hydroxyvalerate (PHBV) is a biodegradable aliphatic polyester.