This document provides an overview of polymers and rubber. It defines key polymerization terms like monomer, polymer, degree of polymerization, and discusses different types of polymerization including addition, condensation, and copolymerization. Natural rubber is made of polyisoprene and has limitations like low strength and reactivity which are addressed by vulcanization through crosslinking with sulfur. Commercial rubbers like Buna-S are discussed which is a styrene-butadiene copolymer used to make tires and insulation due to its tough mechanical properties.

1. Polymers
An Introduction to Polymer Chemistry

2. Contents
• Polymers: Introduction and definition of important
terms – monomer, polymer, polymerization, degree of
polymerization, tacticity, and melting-glass transition
temperature.
• Plastics: Thermosetting & Thermoplastics,
Compounding of plastics, Preparation, properties and
applications of commercial plastics (PF, PMMA)
• Elastomers: Natural rubber, drawbacks of natural
rubber, Vulcanization of rubber. Preparation, properties
and applications of commercial elastomers (Buna-S,
Isocyanate rubber)
• Speciality polymers: Conducting polymers, Self-
healing polymers. Applications of specialty polymers.

3. • Polymer (Greek: poly=many; mer=part)
giant, complex molecules
• Made up by the linking together of large number of
small molecules (repeating units called monomers )
held together by covalent bonds (two or more bonding
sites)
Introduction

4. Monomers
Alkenes, vinyl chloride, adipic acid, glucose, amino acids, glycol
with two bonding sites act as monomers
C C
H
H
H
H
E t h y le n e
Aminoacid
ethane-1,2-diol
hexane-1,6-diamine
adipic acid
terephthalic acid
Isoprene

5. Butadiene, MW 54 Polybutadiene, MW 200000
Polymerization
MW 28 MW 28000
Monomer Polymer
Process in which low molecular weight compounds combine to
form giant molecules/ macromolecules of high molecular weight
n

6. Degree of Polymerization
• Number of repeating units in the polymer chain
formed is called the degree of polymerization
(n).
• Polyethene: (C2H4)n, where n stands for DP
• Molecular weight of PE, M = nMo,
where Mo is molecular weight of monomer
• Strength of the polymer can be increased by
increasing its DP
– High DP hard and heat resistant
– Low DP  soft, gummy

7.  Molecular mass between 28,000 and
280,000
 Light, flexible
 Low melting point
 Used to make soft items (e.g. wash
bottles, plastic bags and food wraps)
Low Density Polyethene (LDPE)

8. High density polyethene (HDPE)

9. • Data: If MW of Polyethyne, M = 28000,
MW of repeat unit, Mo = 28,
M = nMo
• Thus, n = M/Mo
= 28000/28
= 1000
Degree of Polymerization (n) = 1000
Degree of Polymerization

10. Importance of degree of polymerization
• The degree of polymerisation uniquely determines the weight of a
macromolecule of known composition
• The physical and chemical properties of an oligomer change with
increasing molecular weight. There is a certain critical value beyond
which further increase in the molecular weight no longer significantly
affects these properties. This value characterises the transition from
the oligomer to the polymer, and it differs for different properties.
• Polydisperse polymers are described by different molecular weight
averages, and a complete characterisation is given by the molecular
weight distribution.
• Molecular weight distribution can be characterised as weight-
average Mw and z-average molecular weights that correspond to
other ways of averaging over a set of macromolecules.

11. Classification
i) On the basis of origin
– Natural
– Synthetic
ii) On the basis of nature of repeat unit
• Homopolymers (comprise of monomers of the same type)
– Linear (homochain or heterochain)
– Branched
– Cross-linked
• Heteropolymers/ Copolymers (Different repeating units)
– Linear; Branched; Graft (regular/irregular); Block
(regular/irregular)
iii) On the basis of chemical nature
• Organic (polymer backbone chain made up of carbon atom)
• Inorganic (No carbon atoms in the backbone chain, eg., Silicone
rubbers)

12. Homopolymer: Monomers of the
same type
Copolymer: Different repeating units
Random copolymer: Two or more different repeating units are
distributed randomly
Alternating copolymer: Alternating sequences of different monomers
Block copolymer: Long sequences of a monomer are followed by long
sequences of another monomer
Homopolymers can be linear,
branched or cross-linked
Nomenclature

13. Graft copolymer: Chain made from one type of monomer
with branches of another type

14. Tacticity: Orientation of monomeric units in polymer takes
place in orderly/disorderly fashion w.r.t main chain.
The difference in configuration affects their physical
properties
Isotactic: Head-to-tail configuration
Functional groups are all on the same side of the main
chain, FG= Y
Tacticity:
Natural rubber is example of isotactic

15. Syndiotactic: Functional groups occupy alternating position.
Atactic: Functional groups arranged in random manner
For example, atactic polypropylene is a gummy solid, while isotactic
version is highly crystalline & tough.
Tacticity:
Guttapercha is example of syndiotactic

16. • Polymerization
Fundamental process in which low molecular weight
compounds combine to form giant molecules/
macromolecules of high molecular weight
Three types of polymerization
• Addition
• Condensation
• Copolymerization
Types of Polymerization

17. Addition Polymerization
• Formed from the monomer, without the loss of any
byproduct, like small molecules. Monomers with
double or triple bonds tend to polymerize without the
liberation of small molecules. Example: Polyethylene
(PE)
• It yields product that is an exact multiple of the original
monomer unit

18. Common Polyolefins
Monomer Polymer
Ethylene
H3C
CH3
n
Repeat unit
Polyethylene
CH3
CH3
n
CH3 CH3 CH3 CH3 CH3 CH3
CH3
Propylene
Polypropylene
Ph
CH3
n
Ph Ph Ph Ph Ph Ph
Ph
Styrene
Polystyrene
Cl
CH3
n
Cl Cl Cl Cl Cl Cl
Cl
Vinyl Chloride
Poly(vinyl chloride)
F2C CF2
Tetrafluoroethylene
F3C
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
CF3
n
Poly(tetrafluoroethylene): Teflon

19. Condensation/Step Polymerization
• Formation of polymers from polyfunctional monomers
of organic molecules with elimination of small
molecules like water, HCl
• Functional group of one monomer unit reacts with
functional group of the other
• Eg- Nylon-66 (hexamethylene diamine + adipic acid)

20. Polyesters & Amides
Monomer Polymer
CO2H
HO2C
HO
OH
O O
HO O
H2
C
H2
C O
n
Terephthalic
acid
Ethylene
glycol
Poly(ethylene terephthalate
H
Ester
HO OH
O O
4
H2N NH2
4
Adipic Acid 1,6-Diaminohexane Nylon 6,6
HO N
H
N
H
H
O O
4 4
n
CO2H
HO2C
Terephthalic
acid
NH2
H2N
1,4-Diamino
benzene
Kevlar
O
HO
O
H
N
H
N H
n
Amide

21. Natural Polymers
Monomer Polymer
Isoprene
n
Polyisoprene:
Natural rubber
O
H
HO
H
HO
H
H
OH
H
OH
OH
Poly(ß-D-glycoside):
cellulose
O
H
O
H
HO
H
H
OH
H
OH
OH
H
n
ß-D-glucose
H3N
O
O
R
Polyamino acid:
protein
H3N
O
H
N
R1
O
H
N
Rn+1
O
OH
Rn+2
n
Amino Acid
Base
O
OH
O
P
O
O
O
oligonucleic acid
DNA
Nucleotide
Base = C, G, T, A
Base
O
O
O
P
O
O
O
DNA
DNA

22. Copolymerization
• Specific type of addition polymerization, without loss
of any small molecules
• Monomers of more than one type are involved thereby
giving variety of polymers
• Eg. Styrene-Butadiene rubber (Buna-S)

23. Polymer Crystallinity
• Polymers are never completely crystalline crystalline
regions with amorphous regions are together
• Polymer is crystalline if all molecules are arranged in an
orderly manner with symmetrical orientation
• Degree of crystallinity depends on DP & tacticity
• Crystalline polymers possess high density, sharp melting
points, strong, brittle and hard
• Amorphous polymers do not possess melting points,
but softening points

24. Melting and Glass transition temperatures
• Lowest temperature beyond which polymer becomes
hard, brittle, glass-like or temperature at which polymer
experiences transition from rubbery to rigid states is
called glass transition temperature (Tg)
In this state, solid tends to shatter if it is hit, since the
molecular chains cannot move easily.
• Temperature above which polymer turns out to be
flexible, elastic and rubbery (Tm)

25. Beyond glass transition temperature, crystalline and amorphous
polymer behaves differently as shown in the diagram below.
Effect of heat on polymer

26. Significance
• Tg and Tm are significant parameters
• Gives an indication of the temperature region at which
a polymeric material transforms from a rigid solid to a
soft viscous state
• Helps in choosing the right processing temperature in
which materials are converted into finished products

27. Factors affecting Tg
• Tg is directly proportional to the molecular
weight of the polymer.
• Greater the degree of cross-linking, higher the Tg.
• Polymers with strong intermolecular forces of
attraction have greater Tg.
• Side groups, especially benzene and aromatic
groups attached to main chain increases Tg.

28. Number average Molecular weight
• Consider a polymer sample in which n1, n2 and n3… are number
of molecules with molecular weights M1,M2,M3…respectively
then,
=
=
Where, ni is number of molecules of mass Mi
Molecular Weight

29. Number of Molecules, Ni Mass of Each Molecule, Mi
Total Mass of Each Type of
Molecule, NiMi
1 800,000 800,000
3 750,000 2,250,000
5 700,000 3,500,000
8 650,000 5,200,000
10 600,000 6,000,000
13 550,000 7,150,000
20 500,000 10,000,000
13 450,000 5,850,000
10 400,000 4,000,000
8 350,000 2,800,000
5 300,000 1,500,000
3 250,000 750,000
1 200,000 200,000
Total Mass = NiMi = 50,000,000
NiMi, where Ni is the number of molecules of weight Mi
Ni = 100
The number average molecular weight for this sample is then,
NiMi / Ni = 50,000,000/100 = 500,000
The number average molecular weight

30. In 1953, Hermann Staudinger
formulated a macromolecular structure
for rubber and received the Nobel Prize.
isoprene
 based on the repeating unit
2-methylbuta-1,3-diene
Rubber

31. Elastomers/ Rubbers
• The polymers possessing elasticity to the extent of
nearly 200 to 300 percent are known as Elastomers
or Rubber
• Amorphous polymer with numerous cross linkages
and high degree of elasticity deformed by
stretching & regain original form when stretching
force is removed
• Rubber has no crystallinity. Their extension and contraction are
due to temporary movements of segments of polymer chain.
The chains do not slip past each other due to cross linkages
U n s t r e s s e d R u b b e r S t r e s s e d R u b b e r
A p p l i e d r e le a s e o f
S t r e s s
s t r e s s
B a c k t o
o r i g in a l p o s i t i o n

32. Properties of Rubber
Important properties of rubber are its
• Flexibility
• Strength
• Impermeability to water
• High resistance to abrasion etc,
Due to these properties rubber is highly useful for industrial as well
as domestic purposes.

33. Types of Rubber
 Natural Rubber- Obtained from natural sources
 Synthetic Rubber- Made synthetically

34. • Raw material from rubber tree (Hevea
brasiliensis) is tapped every second day for its
sap, known as latex, by making slanting cuts in
the bark of the tree.
• Latex is collected and acetic acid is added to it so
as to precipitate out the rubber, which then
hardens/coagulates.
• After being washed and dried, rubber is cured in
special smokehouses to protect it against
microbial attack.
• Purer the rubber, higher the grade – it is ready
for delivery to rubber companies worldwide.
Natural Rubber

35. • Natural Rubber
• Polymer of isoprene (2-methyl-1,3-butadiene)
• Low tensile strength, elasticity over a narrow
range of temperature
Rubber
Destructive
distillation
Isoprene
Dipentene
+
Molecular weight of rubber is very high of
about 300,000.

36. Structure of Rubber
Rubber which is composed of all cis-linked isoprene units,
forms an amorphous structure that is highly elastic. On the
other hand, gutta percha, which is a polyisoprene compound
made of all trans-linked isoprene units, forms linear strands
which can interact into crystalline arrays that have plastic
properties, but are not elastic.

37. • Its plasticity is greater than elasticity. It can’t sustain
stress. Thus when stretched to a great extent, it
undergoes deformation permanently
• It has large water absorption tendency, which make it
week
• Limitations of natural rubber: It softens at high
temperature and becomes brittle at low temperature.
• Natural rubber is attacked by acids, oxidizing agents,
non-polar solvents and oxidized by air.
To overcome these limitations rubber is vulcanized.
Drawbacks of Natural rubber

38. Vulcanization
• Vulcanization is a process which is essentially
compounding rubber with different chemicals like
sulphur, H2S, benzoyl chloride etc.
• Heating raw rubber with sulphur at 100 -140 ˚C.
Sulphur enters the double bonds of rubber and forms
cross-linkages. Excellent changes in properties,
resistance to changes in temperature, increased
elasticity, tensile strength, durability, chemical resistance
• Brings about stiffening of rubber by anchoring &
restricting intermolecular movement by providing
cross-linkages between chains.

39. Vulcanization

40. • The toughness or stiffness of vulcanization
depends on the amount of sulphur included
• For flexible tyre rubber, sulphur content is
from 3-5% whereas for tougher variety like
ebonite, content of sulphur is 32 %
• Ebonite is so tough that it can be machined
and has very good electrical insulation property.

41. Property Raw Rubber Vulcanized Rubber
Elasticity Very high Low, depending on % S
Tensile Strength 200 kg/cm2 2000 kg/cm2
Chemical resistance Very poor Higher
Durability Less Higher
Quality Inherent Can be controlled by
vulcanization

42. Applications of rubber
• Due to remarkable resistance to electricity, it is used as
an insulating coating on wires and cables, used for
electric power transmission
• Due to its elasticity, it is used to fabricate rubber
bands, rubber goods, golf balls, tubes for automobiles,
etc
• It acts as an excellent adhesive
• Foam-rubber is used for making pillows, cushions,
mattresses, automotive pads, etc.
• Polysulfide rubber is used as a solid-propellant fuel for
rocket motors.

43. Preparation, Properties and Uses of
Commercial Rubbers

44. Copolymerization of butadiene & styrene carried out at 5oC
Good and tough mechanical properties
Easily attacked by oxidizing agents, mainly ozone, organic solvents
Uses: Manufacture of tyres, insulating wires and cables, adhesives,
lining of vessels
Buna-S Rubber/Cold Rubber
Synthetic rubber is any vulcanizable man-made rubber-like polymer
which can be stretched to twice its length and on releasing the stress, it
returns to its original shape and size.

45. Polyurethane (Isocynate) Rubber
• Ethylene glycol polymerizes with ethylene diisocyanate to form
polyurethane rubber.
• Highly resistant to oxidation
• Resistant to organic solvents, attacked by acids and alkali
Uses: surface coatings and manufacture of foams and fibers

46. The world consumption of synthetic polymers :
150 million metric tons per year.
1) Plastics : 56%
2) Fibers : 18%
3) Synthetic rubber : 11%
4) Coating and Adhesives : 15%
Industrial Polymers

47. Plastics
ThermoPlastics/Thermosoftening Polymers
• Some polymers when heated become soft and can be
moulded into any shape that can retain on cooling
• PVC, PE, nylon sealing wax, etc
Thermosetting polymers
• On heating, polymers undergo a chemical change and
become an infusible mass which cannot be reshaped
• Bakelite, polyester, resins
The polymeric materials, which are rigid, dimensionally
stable and usually brittle are known as plastic.

48. Thermoplastic polymers Thermosetting polymers
They soften on heating and harden on
cooling
They are fusible on initial heating, but
turn into hard infusible mass on heating
further
Can be reshaped and recycled Cannot be reshaped and recycled
Formed by addition polymerization Formed by condensation polymerization
Linear in structure Three dimensional in structure
They are soluble in some organic solvents Insoluble in organic solvents
Moulded articles are taken out after cooling
the mould to avoid deformation of the
article
Moulded articles are taken out from the
mould even when they are hot.
e.g. Polyethylene, polystyrene, PVC, PVA e.g. Nylon 6:6, Phenolformaldehyde,
ureaformaldehyde,
Comparisons

49. Compounding of Plastics
• Unusual for a finished high polymeric articles to solely
consist of high polymers alone
• Mixed with ingredients known as additives resulting in
useful functions and imparts useful properties to the
finished products
• Main types of compounding ingredients are
– Resin: Binder, which holds different constituents/additives
together. Natural or synthetic resins used in this case

50. • Plasticizers: Low MW organic liquids added to polymer to
improve its flexibility; Added 8-10% of total bulk of plastics
(oils, camphor, dioctyl phthalates) The small molecules penetrate
into the polymer matrix and neutralize a part of intermolecular
forces of attraction between macromolecules and increase
mobility of polymer segments so that chains can slide over each
other. Hence, plasticizers act as an internal lubricant

51. • Stabilizers: Most polymers do not possess chemical
stability change colors & decompose
– Stabilizers are additives which chemically stabilize the polymer
and thus arrest degradation
– Organic, inorganic, organometallic compounds like CaO, BaO,
Organo-tin compounds
• Fillers/Extenders: Inert material added to enhance
mechanical strength-- asbestos powder, saw dust, cotton
pulp, clay, etc
• Lubricants: Glossy finish to product, Prevents plastics
from sticking to fabrication equipments; oils, waxes,
soaps, etc

52. • Catalysts
Antioxidants like H2O2, benzoyl peroxide, ZnO, NH3,
Ag, Pb, are added to the polymeric matrix to accelerate
the cross linking in thermosetting plastics while
moulding process
• Coloring materials
Organic dyes and pigments impart desired color for
aesthetic appeal of the finished polymeric material.
Some colors are added to impart UV protection to the
finished products.

53. Preparation, Properties and Uses of
Commercial Plastics

54. Phenol Formaldehyde Resin
Acid or a base as a catalyst to undergo condensation polymerization
product nature depends on the catalyst and ratio of phenol and
formaldehyde. Novolac resin is a linear thermoplastic polymer, whereas
Bakelite is a cross-linked thermosetting polymer.

55. Phenol Formaldehyde Resin

56. Properties and Uses
• Phenolic resins are rigid, hard, water resistant
• Resistant to acids, salts, organic solvents
• Easily attacked by alkalies due to the presence of free
hydroxy groups
• Possess electrical insulating properties due to low
thermal conductivity
• Uses:
– Used to fabricate insulators, plugs, switches
– Used as cation-exchanger resin in water softening
– Adhesives in paints and varnishes
– Propellar shafts for paper industry and mills

57. Poly(methyl methacrylate) (PMMA)
• Poly(methyl methacrylate) (PMMA) is a transparent
thermoplastic often used as a lightweight or shatter-resistant
alternative to glass
• Although it is not technically a type of glass, the substance has
sometimes historically been called acrylic glass
• Chemically, it is the synthetic polymer of methyl methacrylate.

58. Property

59. Applications of PMMA
 Safety glass such as Plexiglass and Lucite – uses range
from windows for aquariums and under-water
restaurants to safety shields at hockey rinks to skylights
in your home to simple paperweights
 Used as bone cement for use in arthroplastic
procedures of the hip, knee, and other joints for the
fixation of polymer or metallic prosthetic implants to
living bone
 Used in Pacemakers
 Artificial eye lenses used for cataract surgery

60. Urea formaldehyde resin
Monomethylol urea on polymerization, yields a linear UF resin polymer

61. Urea formaldehyde resin

62. • Urea-formaldehyde resin yields clear, water-white
products.
• Hardness, tensile strength is comparatively better than
phenolic resins
• Better heat & moisture resistance
Uses:
• Adhesives for plywood, decorative laminates- surface
coatings
• Due to their colorability, solvent, grease resistance
cosmetic containers
• Electrical insulation
Property and uses
Properties:

63. Conducting Polymers
• Polymers are poor conductors of electricity, due to non-
availability of large number of free electrons
• Polymers with polyconjugated structures are insulators in
pure state, but when treated with oxidizing or reducing
agents can be converted into polymer salts with electrical
conductivities comparable to metals.
Ex: polyacetylene, a poor conductor in its pure state
could be turned into a highly conductive polymer by
conversion to salt on reacting it with iodine. The result
was a dramatic increase of over 1010 in conductivity

64. • Conductivity increases by decreasing the energy
band gap
• Amount of energy needed to promote an
electron from valence to empty band
(conduction band)
• Polymers have large band gaps, with careful
design of chemical structure of polymeric
backbone  band gap = 0.5 to 1eV
Conducting Polymers

65. Conditions
• Polymer should consist of alternating single and
double bonds called conjugated double bonds
• Polymer matrix has to be disturbed –
– Either by removing electrons from them (oxidation),
– Or inserting electrons into the material (reduction).
The process is known as doping
– By doping with electron donor like alkali-metal ion
or electron acceptor like AsF5, Iodine, etc polymers
turn conductive materials

66. • Iodine molecule attracts an electron from polyacetylene chain and
becomes I3
-
• Polyacetylene molecule, now positively charged, is termed a radical
cation, or polaron
• Lonely electron of the double bond, from which an electron was
removed, can move easily.
• As a consequence, double bond successively moves along the
molecule– Conducting Polymers

67. • π-electron conducting polymers: In these polymers, backbone of
the polymer is made up of molecules that contain conjugated π-
electrons which extend the entire polymer and make the polymer
conducting.
• Conducting element-filled polymer: Here, polymer acts as a
binder that binds the conducting elements like carbon black, metal
oxides, metallic fibres that conduct electricity.
• Inorganic polymer: A metal atom with polydentate ligand, which is
a charge transfer complex is bound to the polymer to make it
conducting.
• Doped- conducting polymer: Polymer is made conducting by
exposing the surfaces to charge transfer agents in gas or in solution
phase.
• Blended conducting polymer: This polymer is made by blending a
conventional polymer with a conducting polymer.
Conducting polymers are classifications

68. Conducting
Polymers
Telecommunicati
on
Aerospace
Battery
technology
Smart Materials
Applications

69. Self healing polymers
• Inspired from biological systems  ‘Wound healing’
• Inherent ability of polymers to repair damage caused by
mechanical usage over time
• Terminator Polymers
• Chemistry World posted a video of the product in action,
showing someone cutting a piece of the polymer in two with a
scalpel, pressing the pieces back together and leaving it on a table
for two hours at room temperature. The person is unable to pull
the material apart with their hands upon returning.
• This is the next generation breakthrough in polymers.

70. • Autonomic healing: A propagating crack ruptures the
microcapsules, releasing the healing agent into the crack
plane by capillary action. Polymerization is initiated by
contact with the embedded catalyst or initiator, bonding
the crack faces, and restoring structural continuity.

71. • Non-autonomic healing: Partially self-
contained; healing capability is designed into the
material, but additional external stimuli such as
heat or UV-radiation is required for the healing
to occur.

72. Applications
• Nissan Motor Co. Ltd has commercialized
world’s first self-healing clear coat for car
surfaces-trade name of this product is ‘Scratch
Guard Coat’
• Self healing concretes– in progress
• Self-healing materials are now used as composites
in aircrafts.

73. Thank you