Learning outcomes:

After studying the current module, students will be able to-

1. classify polymers on the basis of their origin, structure, monomeric units and mode of polymerisation reaction.

2. name polymers and identify the monomers from which the polymers are built.

3. understand the mechanisms of chain and growth polymerisation.

4. examine, how the structure of polymer and the type of forces present in them affect their physical and mechanical properties.

5. study the senior level polymer science curriculum with sufficient knowledge of the preliminary/ basic aspects of polymer science.

Polymers are macromolecules, having high molecular mass and are composed of a large number of repeating units called, ‘Mer’. These repeating units are derived from simple and reactive molecules known as ‘Monomers’. The process of formation of polymer from respective monomers is called ‘Polymerisation’.

monomer $\mathrm{CH} _{2}=\mathrm{CH} _{2}$

Repeating unit/Mer $=-\mathrm{CH} _{2}-\mathrm{CH} _{2}-$

No. of repeating units in a polymer is ‘degree of polymerisation’

Classification of polymers:

1) Based upon their origin-

a) Natural polymers: these are found in plants and animals, e.g. proteins, cellulose, starch, natural rubber.

b) Semi-synthetic polymers: these are derived from natural polymers, e.g. cellulose acetate, cellulose nitrate

c) Synthetic polymers: these are man made polymers, synthesised in laboratory. e.g. plastic, synthetic fibre, synthetic rubber (Buna-S) etc.

2) Classification based upon their structure:-

a) Linear polymers: These are one dimensional polymers, having long and straight chains. e.g. polyethylene, Polyvinyl chloride, polyesters etc.

b) Branched chain polymers: These are 2-D polymers, whose linear chains are having some branching e.g. LDPE (Iow density polyethylene)

c) Cross linked polymers: These are 3-D polymers, formed by bifunctional, trifunctional polymers containing strong covalent bonds between linear polymeric chains e.g. bakelite, melamine etc.

3) Classification based upon type of monomeric units:-

a) Homopolymers- Polymers whose repeating structural unit is derived from only one type of monomer units are called homopolymers. For example, polythene, polypropylene, PVC, polyisoprene, neoprene, polyacrylonitrile, nylon-6, teflon, cellulose, starch

b) Copolymers- Copolymers are polymers in which the repeating structural units are derived from two or more monomer units - nylon-6, 6 , buna-S, polyesters, alkyd resins, bakelite.

4) On the basis of molecular forces of attraction polymers have been divided into the following four categories:

a) Elastomers have the weakest intermolecular forces of attraction between the polymer chains. For example Natural rubber, vulcanized rubber, buna-S, buna-N

b) Fibres are polymers in which the intermolecular forces of attraction are the strongest. These intermolecular forces may be either $\mathrm{H}$-bonding between $\mathrm{N}-\mathrm{H}$ and $\mathrm{C}=0$ groups or dipole-dipole interactions between the polar carbonyl groups in polyesters or cyano groups in orlon, acrilan.

c) Thermoplastics are polymers in which the strength of intermolecular forces are in between those of elastomers and fibres. For example, Polythene, polypropylene, polystyrene, PVC, teflon, polyvinyl acetate, polyacrylonitrile, polymethacrylate. Thermoplastic polymer can be melted on heating and can be obtained again without any change.

d) Thermosetting polymers: Low molecular weight, semifluid substances which when heated in a mould undergo change in chemical composition to give a hard, infusible and insoluble mass are called thermosetting polymers, e.g. bakelite, urea-formaldehyde, melamine-formaldehyde. Thermosetting polymer can be heated only once when it permanently sets into a sold which cannot be remelted and reworked.

5) On the basis of mechanism of polymerisation, they are of two types- (a) Addition/ chain growth polymerisation (b) Condensation/step growth polymerisation

a) Addition/chain growth polymerisation: In this same/different monomers possessing double or triple bonds, add together through covalent bonds and polymerisation takes place due to increase in chain via free radical or ionic species as intermediates. Initiators are required to initiate the reaction. These are of three types (i) free radical (ii) cationic (ii) anionic

(i) Free radical addition polymerisation:

- Initiator:- Peroxides, like benzoyl peroxide

Example:- Polymerisation of ethene to polythene

3 step mechanism:

- Chain initiating step:

- Chain propogating step:

- Chain terminating step:

Step 1: By combination of free radicals

Step 2: By disproportionation of free radicals

other examples: Formation of PVC, PS, Buna-N, Buna-S etc.

ii) Cationic polymerzation: initiator $=\mathrm{BH} _{3}-\mathrm{H} _{2} \mathrm{O}$ that provides $\mathrm{H}^{\oplus}$ Mechanism:

- Chain initiation step:

- Chain propogation step:

Chain termination step:

• Greater the stability of carbocation intermediate easier the polymerisation

$\therefore$ monomers should be

$G=$ electron donating group to stabilise intermediate carbocation $=\mathrm{CH} _{3} / \mathrm{C} _{6} \mathrm{H} _{5}$ etc.

• Examples: polymerisation of styrene to polystyrene

$\qquad \qquad \qquad$ polymerisation of propene to polypropene

iii) Anionic polymerization:

• Initiator = strong base like $\mathrm{KNH} _{2}$

- Mechanism:-

- Chain initiating step:

- Chain propogation step:

- Chain termination step:

• Greater the stability of carbanion, easier the polymerisation.

$\therefore$ monomers should be

$ \mathrm{G}=\text { electron withdraing group like } \mathrm{Cl}, \mathrm{CN}, \mathrm{COCH} _{3} \text { etc. } $

• Examples: polymerisation of vinylchloride $(\mathrm{G}=\mathrm{Cl})$ to polyvinylchloride
  $\hspace{1.4cm}$polymerisation of acrylonitrile ( $\mathrm{G}=\mathrm{CN}$ ) to polyacrylonitrile (PAN)
  $\hspace{1.4cm}$polymerisation of methyl methacrylate $\left(\mathrm{G}=\mathrm{COCH} _{3}\right)$ to
  $\hspace{1.4cm}$plymethylmethacryate (PMMA)

b) Condensation/step growth polymerisation:

These are formed by repeated condensation reaction between two bifunctional or trifunctional monomer units, usually with the elimination of small molecules like water, alcohol, ammonia, carbondioxide, hydrochloric acid etc.

If two reacting molecules have one functional group each, the reaction stops after one step. For example, acetic acid reacts with ethyl alcohol to form ethyl acetate in one step:

If one of the reacting molecules has two functional groups and the other has one functional group, i.e. acetic acid and ethylene glycol, the reaction stops after two steps:

(i)

(ii)

If both the reactants are bifunctional, i.e., have two functional groups each, they undergo a series of condensations in a stepwise manner with the loss of simple molecules like water, alcohol at each step leading ultimately to the formation of a high molecular mass condensation polymer.

- POLYAMIDES (Condensation polymers)

Polymers which have amide linkages are called polyamides. These are prepared by the condensation polymerization of dibasic acids with diamines or their equivalents.

a) Nylon 6,6

(Here, 6, 6 indicates the no. of carbon atoms in diamide and dibasic acid, respectively)

b) Nylon 6, 10

( 6,10 is number of ’ $C$ ’ in diamine & diacid, respectively)

c) Nylon 6

- POLYESTER (Condensation polymer)

Polymers which have easter linkages are called plyesters and are prepared by the condensation polymerisation of diacids with diols.

*Nylon, orlon and dacron are true synthetic fibers. Rayon is semisynthetic fiber derived from cellulose

- RUBBERS (Addition polymers)

a) Natural Rubber:- An elastomer, manufactured from rubber tree (Haevia braziliansis) latex. It is polymer of isoprene, formed by 1,4 addition polymerisation. Also known as cis 1,4 polyisoprene (all double bonds are cis). Exhibits elastic properties due to presence of weak vanderwaal’s interactions.

cis - polyisoprene (Natural rubber)

- Vulcanization: Natural rubber, at high temperature becomes soft and sticky, losses its elasticity and tensile strength. To improve its physical properties, it is heated with sulphur at high temperature to give a crosslinked structure having sulphide linkages. This is known as vulcanisation. Vulcanised rubber is hard and more flexible.

b) Synthetic rubber: Synthetic rubber may be defined as any vulcanisable rubber like polymer which is capable of getting stretched to twice its length. However, it returns to its original size and shape when the stretching force is withdrawn.

(i) Neoprene

(ii) Buna-N (Butadiene-acrylonitrile copolymer)

(iii) Buna-S (Butadiene-styrene copolymer)

- BIODEGRADABLE POLYMERS

Polymers such as polysaccharides (starch, cellulose, etc.) proteins and nucleic acids which control the various life processes are called biopolymers. All these biopolymers disintegrate by themselves in biological systems during a certain period of time by enzymatic hydrolysis and to some extent by oxidation and hence are biodegradable. As a result, they do not cause any pollution.

(i) Poly- $\beta$-hydroxybutyrate-co- $\beta$-hydroxyvalerate (PHBV)

(ii) Nylon 2, Nylon 6

It is a biodegradable step-growth copolymer.

Some polymers, their starting units and uses:

A. Addition homopolymers:-

S.No	Name	Monomer	Polymer structure	Uses
1.	Polythene (PE)	$\mathrm{CH} _{2}=\mathrm{CH} _{2}$	$\left(\mathrm{CH} _{2}=\mathrm{CH} _{2}\right) _{n}$ (a) LDPE: Low density Polythene (highly branched, flexible) (b) HDPE: High density polythene (less branching, tough)	LDPE is used for making toys, squeeze bottles, flexible pipes. HDPE is used for making containers, bottles etc
2.	Polypropene (PP)	$\mathrm{CH} _{3}-\mathrm{CH}=\mathrm{CH} _{2}$ propene		Manufacture of toys, ropes, pipes, fibres etc.
3.	Polystyrene (PS)	styrene		As wrapping materials, toys, disposable glasses, plates etc.
4.	Polyvinyl chloride (PVC)	$\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{Cl}$ vinylchloride		PVC water piping, hand bags, raincoats, vinyl flooring etc.
5	ORLON/ Polyacrylo-nitrile (PAN)	$\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{CN}$ vinylnitrite		Substitute to wool in making commercial fibres orlon or acrilan
6.	Polymethylmeth-acrylate (PMMA)	methylmeth acrylate	PMMA or PLEXIGLASS/LUCITE	Windscreens, solar panels, lighting fixtures, air craft windows
7 .	Teflon	$\mathrm{CF} _{2}=\mathrm{CF} _{2}$		Nonstick surfaces, cable insulation
8.	polyisoprene	isoprene (2-methyl, 1, 3-butadiene)		Natural rubber (elastic) Guttapercha (non crystalline)
9.	Neoprene	chloroprene		For making gaskets and hoses.
B.	Addition copolymers:-
10.	Buna-N (NBR)	$\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH} _{2}$ $(1,3$-Butadiene $\quad+$ $\mathrm{H} _{2} \mathrm{C}=\mathrm{CH}-\mathrm{CN}$ (acrylonitrile)		Making oil seals and tank lining etc.
11.	Buna-S (SBR)	$\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH} _{2}$ $(1,3$-butadiene $)$ $\quad+$ (styrene)		Cable insulations, auto tyres, floortiles etc.
C.	Condensation polymers:-
12.	Terylene/ Dacron	(Terephthalic Acid) + $\mathrm{HO} _{2}-\mathrm{CH} _{2}-\mathrm{CH} _{2}-\mathrm{OH}$ (Ethan-1, 2-diol)		Synthetic fabric
13.	Glyptal	(Phthalic Acid) $\quad+$ $\mathrm{HO}-\mathrm{CH} _{2}-\mathrm{CH} _{2}-\mathrm{OH}$ (Ethan-1, 2-diol)		Manufacture of paints and Lacquers
14 .	Nylon 6, 6	$\mathrm{HOOC}-\left(\mathrm{CH} _{2}\right) _{4}-\mathrm{COOH}$ (Adipic Acid) $\quad+$ $\mathrm{H} _{2} \mathrm{~N}-\left(\mathrm{CH} _{2}\right) _{6}-\mathrm{NH} _{2}$ (Hexamethylenediamine)		Textile industry, in making bristles for brushes.
15.	Nylon-6			Fabrics, tyre, cords, ropes
16.	Thiokol	$\mathrm{Cl}-\mathrm{CH} _{2}-\mathrm{CH} _{2}-\mathrm{Cl}$ (ethylene Chloride) $\quad+$ $\mathrm{Na} _{2} \mathrm{~S} _{4}$ (Sodium polysulphide)		For making hoses and engine gaskets
17.	Urea-formaldehyde resin	$\begin{gathered}+ \\ \text { HCHO } \\ \text { (formaldelyde) } \end{gathered}$		Making unbreakable cups,laminated sheets etc.
18.	Melamine polymer			Making unbreakable crockery
19.	(i) Novolac (Linear phenol- formal- delyde) polymer	$\begin{gathered} + \\ \text { HCHO } \\ \text { (formaldelyde) } \end{gathered}$		It is used in paints
	(ii) Bakelite (Cross linked phenol) formaldeyde resin)	$\begin{gathered} + \\ \text { HCHO } \end{gathered}$		For making combs, electric switches, handles of utensils.

SAMPLE QUESTIONS:

1) The polymer containing strong intermolecular forces; $\mathrm{H}$-bonding is -

a) natural rubber

b) teflon

c) nylon 6,6

d) polystyrene

2) The species which can best serve as an initiator for cationic polymerization is:

a) BuLi

b) $\mathrm{LiAlH} _{4}$

c) $\mathrm{HNO} _{3}$

d) $\mathrm{AlCl} _{3}$

3) High density polythene (HDPE) can be prepared by:

a) Free radical addition

b) Cationic polymerization

c) Anionic polymerization

d) coordination polymerization

4) Which of these can undergo cationic polymerization with greater case than $\mathrm{CH} _{2}=\mathrm{CH} _{2}$

a) $\mathrm{CH} _{3}-\mathrm{CH}=\mathrm{CH} _{2}$

b) $\mathrm{CN}-\mathrm{CH}=\mathrm{CH} _{2}$

c) $\mathrm{Cl}-\mathrm{CH}=\mathrm{CH} _{2}$

d) $\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{COCH} _{3}$

5) The straight chain polymer is formed by-

a) Hydrolysis of $\mathrm{CH} _{3} \mathrm{SiCl} _{3}$ followed by condensation polymerization

b) Hydrolysis of $\left(\mathrm{CH} _{3}\right) _{4} \mathrm{Si}$ by addition polymerization

c) Hydrolysis of $\left(\mathrm{CH} _{3}\right) _{2} \mathrm{SiCl} _{2}$ followed by condensation polymerisation

d) Hydrolysis of $\left(\mathrm{CH} _{3}\right) _{2} \mathrm{SiCl}$ followed by condensation polymerisation

Show Answer

Answer:- (c) is bifunctional; undergoes condensation to give linear polymers known as silicones

PRACTICE QUESTIONS

Question 1- Which of the following is false?

a) Artificial silk is derived from cellulose

b) Nylon-6, 6 is an example of elastomer

c) The repeat unit in natural rubber is isoprene

d) Both starch and cellulose are polymers of glucose

Question 2- Among cellulose, polyvinyl chloride, nylon and natural rubber, the polymer in which the intermolecular force of attraction is weakest is

a) Nylon

b) Polyvinyl chloride

c) Cellulose

d) Natural rubber

Question 3- Which of the following structures represents Neoprene polymers?

Question 4- The species which can best serve as an initiator for the free radical polymerization is

a) Benzoyl peroxide

b) $\mathrm{AlCl} _{3}$

c) BuLi

d) $\mathrm{LiAiH} _{4}$

Question 5- Which of the following is a fully fluorinated polymer?

a) Neoprene

b) Teflon

c) Thiokol

d) PVC

Question 6- Natural Rubber is

a) All trans-polyisoprene

b) Chloroprene

c) Buna-S

d) All cis-polyisoprene

Question 7- Which of the following statements is not correct

a) Caprolactam is the monomer of nylon-6

b) Terylene is a polyester polymer

c) Phenol formaldehyde resin is known as bakelite

d) The monomer of natural rubber is butadiene.

Question 8- Which of the following polymers is prepared by condensation polymerization

a) Styrene

b) Nylon-6, 6

c) Teflon

d) Rubber

Question 9- Which of the following is a polymer containing nitrogen

a) Polyvinyl chloride

b) Bakelite

c) Nylon

d) Terylene

Question 10- Which of the following sets forms biodegradable polymers

b) $\mathrm{C} _{6} \mathrm{H} _{5}-\mathrm{CH}=\mathrm{CH} _{2}$ and $\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH} _{2}$

c) $\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{CN}$ and $\mathrm{CH} _{2}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH} _{2}$

d) $\mathrm{H}_2 \mathrm{~N}-\mathrm{CH}_2-\mathrm{COOH} \text { and } \mathrm{H}_2 \mathrm{~N}-\left(\mathrm{CH}_2\right)_5-\mathrm{COOH}$

Question 11- $\left(\mathrm{NH}\left(\mathrm{CH}_2\right)_6 \mathrm{NHCO}\left(\mathrm{CH}_2\right)_4 \mathrm{CO}\right)_n$ is a

a) Copolymer

b) Addition polymer

c) Thermosetting

d) Monopolymer

Question 12-

a) 2-methyl propene

b) styrene

c) propylene

d) ethene

Question 13- Which of the following is a chain growth polymer-

a) starch

b) Nucleic acid

c) polystyrene

d) protein

Question 14- Which of the following can undergo anionic polymerization with greater ease than ethylene $\left(\mathrm{CH} _{2}=\mathrm{CH} _{2}\right)-$

Question 15- Which of the following is correct statement-

a) LDPE is obtained under high pressure and room temperature

b) HDPE is obtained at atmospheric pressure

c) HDPE is more flexible than LDPE

d) HDPE has highly branched structure

Question 16- Which of the following is not a correct match-

Question 17- Orlon is a polymer of:

a) Styrene

b) vinyl chloride

c) acrylonitrile

d) propene

Question 18- For the given polymers:-

$$ \begin{aligned} & 1=\text { Buna-S } \\ & 2=\text { Nylon- } 6,6 \\ & 3=\text { Polythene } \end{aligned} $$

the intermolecular

forces will be in decreasing order

a) $1>2>3$

b) $2>1>3$

c) $3>2>1$

d) $3>2<1$

Question 19- Which is not an example of addition polymerization

a) PMMA

b) PE

c) Neoprene

d) Dacron

Question 20- Trans-1, 4-polyisoprene is known as-

a) Natural rubber

b) PVC

c) Gutta-percha

d) Buna-N

Question 21- The monomer of the polymer

a) $\mathrm{CH} _{2}=\mathrm{CH} _{\mathrm{CH}_3}^{\mathrm{CH} _{3}}$

b) $\left(\mathrm{CH} _{3}\right) _{2}-\mathrm{HC}=\mathrm{C}\left(\mathrm{CH} _{3}\right) _{2}$

c) $\mathrm{CH} _{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH} _{3}$

d) $\mathrm{CH} _{3}-\mathrm{CH}=\mathrm{CH} _{2}$

Question 22- Linear phenol-formaldehyde polymer is known as:

a) Bakelite

b) PMMA

c) Novolac

d) Teflon

Question 23- Biodegradable polymer which can be produced from glycine and aminocaprioic acid is

a) Nylon 6,6

b) Nylon 2-nylon-6

c) PHBV

d) Buna-N

Question 24- The species that can be used as an initiator for anionic polymerization is:

a) BuLi

b) $\mathrm{KNH} _{2}$

c) $\mathrm{LiAlH} _{4}$

d) all of the above

Question 25- Which of the following statements is/are correct-

(i) Rubber is natural polymer

(ii) Silk is proteneous is nature and polyer of $\alpha$-amino acids

(iii) Bakelite is a modified form of cellulose

(iv) Cotton and jute are cellulosic in nature and a polymer of glucose

a) (i) and (ii) are correct

b) (ii) and (iv) are correct

c) (i), (ii), (iii) are correct

d) (i), (ii), (iv) are correct

Question 26- Teflon/polytetrafluoroethylene is used for nonstrick coating because of-

a) its insulator properties

b) its hardness and greacy appearance

c) its low coefficient of expension

d) its low coefficient of friction

Question 27- Bakelite is a-

a) chain growth and thermosetting polymer

b) thermosetting condensation polymer

c) stepgrowth thermoplastic

d) crosslinked sheet fibre

Question 28- Structure of which of the polymers is not correct-

Question 29- Which of the following is a biodegradable polymer-

a) Cellulose

b) Polythene

c) Nylon-6

d) PVC

Question 30- Which of the following is used for manufacturing unbreakable crockery-

a) PAN

b) PVC

c) Bakelite

d) Malamine resin