Study about polymers.

1. INTRODUCTION
A polymer is a large molecule or a macromolecule which essentially is a combination of many
subunits. The term polymer in Greek means ‘many parts’. Polymers can be found all around us.
From the strand of our DNA which is a naturally occurring biopolymer to polypropylene which
is used throughout the world as plastic.
Polymers may be naturally found in plants and animals (natural polymers) or may be man-
made (synthetic polymers). Different polymers have a number of unique physical and
chemical properties due to which they find usage in everyday life.
Polymers are all created by the process of polymerization wherein their constituent elements
called monomers, are reacted together to form polymer chains i.e 3-dimensional networks
forming the polymer bonds.

2. FUNCTIONALITY OF A MONOMER
•The functionality of a monomer is the number of binding sites that is/are present in that
monomer. For a organic molecule to act as a monomer for polymerization, the minimum
functionality is 2.
•For example, CH₃OH can’t act as monomer for polymerization since it has one functional
group whereas ethylene glycol (HO-CH₂-CH₂-OH) can act as monomer for polymerization
since it has TWO functional groups (Functionality =2)
•Other examples:
•Functionality of ethylene is 2 since it has two reactive sites. For example, the ethylene has two
reactive or bonding sites i.e, there are two new single bonds formed when the ethylene double
bond is broken. So, ethylene is considered to be bifunctional monomer.
• Acetylene has Functionality of four.

3. DEGREE OF POLYMERIZATION
• The degree of polymerization is the number of monomeric units in a macromolecule or polymer
molecule. For example, polyethylene is composed of repeating units (CH₂-CH₂)n where “n” is an
integer number that indicates the degree of polymerization. Mathematically, this parameter is a
ratio of the molecular weights of the polymer and the respective monomer unit.
• The above formula cannot be designed to calculate Dp in copolymers where the monomeric units
are not identical.

4. CLASSIFICATION OF POLYMERS
•Polymers cannot be classified under one category because of their complex structures, different behaviours, and vast
applications. We can, therefore, classify polymers based on the following considerations.
• Classification of Polymers based on the Source of Availability
•There are three types of classification under this category, namely, Natural, Synthetic, and Semi-synthetic Polymers.
•Natural Polymers:
•They occur naturally and are found in plants and animals. For example proteins, starch, cellulose, and rubber.
•Semi-synthetic Polymers:
•They are derived from naturally occurring polymers and undergo further chemical modification. For example,
cellulose nitrate, cellulose acetate.
•Synthetic Polymers:
•These are man-made polymers. Plastic is the most common and widely used synthetic polymer. It is used in industries
and various dairy products. For example, nylon-6, 6, polyester etc.

5. Classification of Polymers based on the Structure of the Monomer Chain
•This category has the following classifications:
•Linear polymers
•In polymers, the monomeric units are connected to each other in the form of long straight
chain are called linear polymers. It is due to close packing as well as high magnitude of
intramolecular forces of attraction in linear polymers which possess high m.p, density and
tensilestrength.
• E.g.: High density polythene (HDPE), Polyester, nylons

6. •Branched chain polymers
•These are linear in nature, but the main chain possesses some branches of monomeric units. These
branches are formed by the replacement of a substituent like hydrogen on a monomeric unit by another
covalently bonded chain of that polymer.
•These branched chain polymers are irregularly packed due to branches so that they have low melting
point, density, tensile strength compared to linear polymers.
• E.g.: Low density polythene (LDPE), Glycogen, Amylopectin.

7. • Cross linked polymers
• These are polymers in which monomeric units are cross linked together by only covalent bonds to
form a three dimensional network (or) cross linked polymers. These are huge molecules in which
movement of individual monomeric units is restricted by strong crosslinks, which cause the
polymer to possess hard, rigid, brittle and do not melt; they burn on strong heating.
• Ex: Bakelite, Urea-Formaldehyde , Melamine-Formaldehyde resin etc.

8. Classification Based on TYPE of Polymerization
•(i) Addition polymerization: In this polymerization process, the monomers add together by
repeating addition without formation of biproducts to form polymer. This process is called as
addition polymerization and the resultant polymer is known as addition polymer.
•This mode of polymerization can takes place through formation of either radicals (or) ionic
species such as carbanions and carbocations.
•E.g.: Polystyrene, Polyethylene, Polyvinyl Chloride (PVC)

9. •(ii) Condensation polymerization: When the molecules of same monomers or different
monomers simply linked together by the formation of low molecular weight byproducts. e.g.:
H₂O, ROH, HCl, etc to form polymer. This process is called as condensation polymerization
and resultant polymer is known as condensation polymer.
•Most of the cases condensation polymers are thermosetting plastics.
•Ex: Terylene (or) Dacron, Polyamides, Nylon-6,6, Polyesters, Proteins etc.

11. Classification Based on types of Monomers
•Based on monomeric units involved in the formation of polymers, which are classified mainly into two types.
•(i) Homopolymers
•(ii) Heteropolymers (copolymers)
• Homopolymers
• The polymer which is formed by consisting of one monomer is called homopolymers:
A A A A A A
• Polymer Monomer
• Polyvinyl chloride Vinyl chloride
• Polyethylene Ethylene
• Polystyrene Styrene
• Natural rubber Isoprene

12. • Heteropolymers (copolymers)
• The polymers which are derived from two or more different types of monomeric units are called
heteropolymers (copolymers): A B B A A B
• Polymer Monomeric Units
• ABS plastic Acrylonitrile + Butadiene + Styrene
• SBR Styrene + Butadiene
• Based on arrangement of monomeric units (structural units) in copolymers which can be classified as
• (a) Alternating copolymers: These polymers are formed by regular alternating of A & B monomeric
units: A B A B A B A B
• (b) Statistical copolymer ( random copolymer): Copolymers in which the sequence of monomer units
follows a statistical rule. The probability of finding a given type monomer unit at a particular point in the
chain is equal to the mole fraction of that monomer unit in a chain:
• A B B B A B A B A A

13. • (c) Block copolymer: The copolymers comprise of two or more homopolymer subunits
linked through covalent bonds are called Block copolymers:
• A A A A B B B B C C C C
• (d) Graft copolymer: Copolymer in which the backbone chain is formed of one type of
monomer and branches are formed of the other.

14. V. Classification Based on Molecular Forces
•Based on magnitude of intermolecular forces, the polymers have been classified into four
categories.
•(i) Thermosetting polymes (or) Thermosets
•(ii) Thermoplastics
•(iii) Elastomers
•(iv) Fibers

15. •(i) Thermosetting polymers (or) Thermosets: These polymers undergo permanent change on
heating i.e. once they have solidified, they cannot be softened during moulding process.
•They are generally prepared from low molecular mass semifluid substances. When heated the
polymers which get highly cross linked (or) three dimensional network structure by strong
covalent bonds to form hard infusible and insoluble products in all solvents.
•These polymers are having permanent rigidity due to the cross links held the molecules in
place so that heating does not allow them to move freely.
•E.g: Bakelite, Melamine Formaldehyde resin, Ureaformaldehyde etc.,

16. •(ii) Thermoplastics: These are linear, long chain polymers that turns to a liquid (soft) when
heated and freezes (hard) with little change in their properties when cooled. i.e., their hardness
is temporarily property, when subject to rise or fall of temperature. The intermolecular forces in
those polymers are intermediate between those of elastomers and fibers. There are no cross
linkings between the monomeric chains, so the chains of polymer moves more freely. Which
results the soften the material. When heated they melt to form a fluid which can be moulded
into any desire shape and then cooled to get the desire product.
•E.g.: Polyethylene, Polystyrene, PVC, Teflon etc.,

17. Difference between Thermoplastics and Thermosetting polymers
Thermoplastics Thermosetting polymers
• These are the product of addition
polymerization.
These are the products of condensation
polymerization.
• They are generally long chain linear
polymers. Monomers are bifunctional.
They have three dimensional cross-linked
structure joined by strong covalent bonds. Uses
higher functional monomers.
• On heating, they soften readily because
weak forces between the chains can be
easily broken.
They do not soften on heating because strong
covalent bonds retain their strengths on
heating.
• They can be softened, reshaped and
reused by heating and cooling processes.
They cannot be softened, reshaped and
reused.
• Weak, soft and less brittle. Hard and strong
• Soluble in organic solvents Insoluble in organic solvents
• Low molecular weight High molecular weight

18. •(iii) Elastomers or synthetic rubber: The polymers which behave viscoelasticity (elasticity) like
rubber are called elastomers. These can be stretched to atleast thrice of its length due to weak
intermolecular forces between the polymer chains. When stretching force is released, they return to
their original shape and dimensions due to covalent cross linkages in the polymer chains. If there are no
covalent cross linkages, the material undergoes permanent deformation by applying the stress.
•E.g: Natural rubber
•(iv) Fibers: Polymer fibers are subset of man-made fibers which are synthesized by chemicals. These
have strong intermolecular forces between the chain due to hydrogen bonds or dipole-dipole
interaction. The chains are well packed because of strong forces giving them high tensil strength and
less elasticity. Therefore these polymers have sharp melting point and are used for making fibers.
•Ex: Nylon, Polyester etc.,

19. Classification Based on Backbone chain of Polymer
•On the basis of the type of the backbone chain, polymers can be divided into:
• Organic Polymers: Carbon backbone. For example, wool, silk, proteins, starch,
and cellulose.
• Inorganic Polymers: Backbone constituted by elements other than carbon. For example,
borates, silicates, silicones, and silanes.

20. Classification Based on Tacticity
•Depending upon the orientation of monomers in the polymer chain, polymers can be classified
into three types
•Isotactic polymer: If the side groups of the monomers lie on the same side of the chain, it is
called an isotactic polymer.
•Syndiotactic polymer: If the side groups of the monomers are arranged in alternate fashion
around the main chain, it is called an syndiotactic polymer.
•Atactic polymer: If the side groups of the monomers are arranged in irregular or random
fashion around the main chain, it is called an atactic polymer.
•

22. Classification Based on Atomic composition
•Homochain polymer:
•When the main chain is made up of the same type of atoms, the polymer is known as
homochain polymer, e.g. polythene, polystryene.
•Heterochain heterochain:
•When the main chain is made up of the different type of atoms, the polymer is known as
heterochain polymer, e.g. nylons, polyesters.
•