Polymers
A polymer is a substance that is made up very large molecules that are, in turn, made
up of many repeating units called monomers. 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.
Polymerization is the process through which the monomers come together to form the
macromolecules that constitute polymers. An illustration detailing the polymerization of
the monomer styrene into the polymer known as polystyrene is provided below.
[Polystyrene is a hard, brilliantly transparent, stiff resin. Polystyrene is insoluble in
water. Polystyrene is compound that is non-biodegradable with a couple of exceptions.
It is easily dissolved by many aromatic hydrocarbon solvents and chlorinated solvents. It
is widely used in the food-service industry as rigid trays, containers, disposable eating
plates, bowls, etc.]
Classification of Polymers based on the Source
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 the chemical equation for the formation of the trinitrate is:
3 HNO3 + C6H7(OH)3O2 H SO → C6H7(ONO2)3O2 + 3 H2O
2 4
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,
polyether’s etc.
Classification of Polymers based on the Structure of the Monomer Chain
Linear Polymers
The structure of polymers containing long and straight chains fall into this category.
PVC, i.e. poly-vinyl chloride is largely used for making pipes and electric cables is an
example of a linear polymer.
Branched-chain Polymers
When linear chains of a polymer form branches, then, such polymers are categorized as branched
chain polymers. For example, Low-density polythene.
Cross-linked Polymers
They are composed of bifunctional and trifunctional monomers. They have a stronger covalent
bond in comparison to other linear polymers. Bakelite and melamine are examples in this category.
Classification Based on Polymerization
Addition Polymerization: An addition polymer is a polymer that forms by simple
linking of monomers without the co-generation of other products. Example, poly
ethane, Teflon, Polyvinyl chloride (PVC)
Condensation Polymerization: Condensation polymers are any
kind of polymers formed through a condensation reaction—where
molecules join together--losing small molecules as by-products such
as water or methanol. Example, Nylon -6, 6, perylene, polyesters.
Classification Based on Monomers
Homomer: In this type, a single type of monomer unit is present. For
example, Polyethene
Heteropolymer or co-polymer: It consists of different type of
monomer units. For example, nylon -6, 6
Classification Based on Molecular Forces
Elastomers: These are rubber-like solids weak interaction forces are
present. For example, Rubber.
Fibres: Strong, tough, high tensile strength and strong forces of
interaction are present. For example, nylon -6, 6.
Thermoplastics: These have intermediate forces of attraction. For
example, polyvinyl chloride.
Thermosetting polymers: These polymers greatly improve the
material’s mechanical properties. It provides enhanced chemical and
heat resistance. For example, phenolics, epoxies, and silicones.
Silicone
Epoxy resin preparation
Types of Polymers
On the basis of the type of the backbone chain, polymers can be divided
into:
Organic Polymers: Carbon backbone.
Inorganic Polymers: Backbone constituted by elements other than
carbon.
Example of inorganic polymers include polysilanes (Si-Si bond),
polysiloxanes ( Si-O bonds pr silicones), polysilazanes ( Si-N bonds ),
polysulfides ( S-S bonds ).
Polysilazane Polysulfide
pentasulfur-titanocene complex
Biodegradable Polymers
The polymers which are degraded and decayed by microorganisms like
bacteria are known as biodegradable polymers. These types of polymers
are used in surgical bandages, capsule coatings and in surgery. For
example, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV]
High-Temperature Polymers
These polymers are stable at high temperatures. Due to their high
molecular weight, these are not destroyed even at very high temperatures.
They are extensively used in the healthcare industries, for making
sterilization equipment and in the manufacturing of heat and shock-
resistant objects.Example-Polyterafluoroethylene (PTFE)
Difference Between Thermoplastics and Thermosetting Plastics:
Sl No Thermoplastics Thermosetting plastics
1. Thermoplastics are linear Thermosetting Plastics are
polymers. cross-linked polymers
They undergo no chemical They undergo chemical
2. change in the molding change in the molding
operation. operation.
They can be softened again They cannot be re-softened
3.
and again. once they hard.
These plastics cannot be
4. These plastics can be reused.
reused.
5. These are soft and flexible. These are hard and brittle.
They are affected by certain They are unaffected by any
6.
solvents. solvent.
Preparation of Some polymers
Terylene
Nylon 6
Caprolactam
Epoxy resin
UPR
EVA
Silicone
Commercial Uses of Polymers
Polymer Monomer Uses of Polymer
Isoprene ( 2-methyl 1, 3- Making tyres, elastic
Rubber (polyisoprene)
butadiene) materials
BUNA – S (a) 1, 3-butadiene (b) Styrene Synthetic rubber
(a) 1, 3-butadiene (b) Vinyl
BUNA – N Synthetic rubber
Cyanide
Non-stick cookware –
Teflon Tetra Flouro Ethane
plastics
(a) Ethylene glycol (b)
Terylene Fabric
Terephthalic acid
Glyptal (a) Ethylene glycol (b) Phthalic Fabric
acid
Plastic switches, Mugs,
Bakelite (a) Phenol (b) Formaldehyde
buckets
PVC Vinyl Cyanide Tubes, Pipes
Melamine Formaldehyde (a) Melamine (b)
Ceramic plastic material
Resin Formaldehyde
Nylon-6 Caprolactum Fabric
