MONOMERS & POLYMERS
• Monomers are small molecules used to
• A polymer is a large molecule made up of
many smaller molecules (monomers).
• The chemical reaction in which the monomers
are joined together by covalent bonds is called
CLASSIFICATION OF POLYMERS
• Homopolymers – synthesised from a single
type of monomer. Example : polyethylene and
These may be represented as : -[A-A-A-A-A-A]• Copolymers – formed from two or more
different types of monomers are called
These may be represented as : -[A-B-A-B-A-B]-
Several classes of copolymer are possible
• Statistical copolymer (Random)
two or more different repeating unit
are distributed randomly
• Alternating copolymer
are made of alternating sequences
of the different monomers
• Block copolymer
long sequences of a monomer are followed
by long sequences of another monomer
• Graft copolymer
Consist of a chain made from one type of
monomers with branches of another type
Classification by Chain structure (molecular architecture)
• Linear chains : a polymer consisting of a single continuous chain
of repeat units
• Branched chains :a polymer that includes side chains of repeat
units connecting onto the main chain of repeat units
• Hyper branched polymer consist of a constitutional repeating
unit including a branching groups
• Cross linked polymer :a polymer that includes interconnections
• Network polymer :a cross linked polymer that includes numerous
interconnections between chains
Direction of increasing strength
NOMENCLATURE / NAMING
Generic source-based nomenclature for
(IUPAC Recommendations 2001)
A generic source-based name comprises two parts:
1) polymer class (generic) name followed by a
2) the actual or hypothetical monomer name(s),
always parenthesized in the case of a copolymer
• The source-based name of a homopolymer is made
by combining the prefix “poly” with the name of the
• A generic source-based name of a polymer has two
components and always parenthesized in the case of a
I. A polymer class (generic) name (polyG) followed by a
II. The actual of hypothetical monomer name(s)
• When more than one type of functional group or
heterocyclic system is present in the polymer
structure, names should be alphabetized, example,
• Polymer class names relevant only to the main chain
are specified in the name, names of side-chain
functional groups may also be included after a
hyphen if they are formed during the polymerization
• In the case of carbon-chain polymers such as vinyl
polymers or diene polymers, the generic name is to
be used only when different polymer structures may
arise from a given monomeric system.
CHARACTERISTICS OF POLYMERS
Low coefficient of friction.
Good corrosion resistance.
Good mould ability.
Excellent surface finish can be obtained.
Can be produced with close dimensional tolerances.
Poor tensile strength.
Low mechanical properties.
Poor temperature resistance.
Can be produced transparent or in different colours.
The physical properties of a polymer, such as its strength
and flexibility depend on:
• Chain length - in general, the longer the chains the
stronger the polymer;
• Side groups - polar side groups give stronger attraction
between polymer chains, making the polymer
• Branching - straight, un branched chains can pack
together more closely than highly branched chains,
giving polymers that are more crystalline and therefore
• Cross-linking - if polymer chains are linked together
extensively by covalent bonds, the polymer is harder
and more difficult to melt.
STRENGTH OF POLYMERS
In general, the longer the polymer chain, the stronger the
polymer. There are two reasons for this:
• longer chains are more tangled
• there are more intermolecular forces between the
chains because there are more points of
contact. These forces, however, are quite weak for
• Areas in a polymer where the chains are closely packed
in a regular way are said to be crystalline. The
percentage of crystallinity in a polymer is very
important in determining its properties. The more
crystalline the polymer, the stronger and less flexible it
• When a polymer is stretched (cold-drawn), a neck
forms. In the neck the polymer chains line up
producing a more crystalline region. Cold-drawing
leads to an increase in strength.
• The first polyethene which was made contained many
chains which were branched. This resulted in a
relatively disorganised structure of low strength and
density. This was called low density polyethene (ldpe).
• In the crystalline form, the methyl groups all have the
same orientation along the chain. This is called the
isotactic form. In the amorphous form, the methyl
groups are randomly orientated. This is called the
• Polymers with a regular structure are said to be
• Both classes of reaction can lead to the formation of
either linear polymers or polymer networks.
Whether the linear chains or polymer networks are
obtained only depends on the number of reactive
entities per monomer.
• In step-growth polymerization, a linear chain results
from the step-wise condensation or addition of
reactive groups of bifunctional monomers.
• Condensation : process in which two monomers
react to form a larger molecule and eliminate a
smaller molecule (usually water, ammonia, methanol
or hydrogen chloride).
• Example : Kevlar, nylon, and Terylene.
• Step-Growth polymerization occurs by consecutive reactions in
which the degree of polymerization and average molecular
weight of the polymer increase as the reaction proceeds.
Usually (although not always), the reactions involve the
elimination of a small molecule (e.g., water). Condensation
polymerization may be represented by the following reactions:
Monomer + Monomer
Dimer + H2O
Monomer + Dimer
Trimer + H2O
Monomer + Trimer
Tetramer + H2O
Dimer + Dimer
Tetramer + H2O
Dimer + Trimer
Pentamer + H2O
Trimer + Trimer
Hexamer + H2O
• Generally, the reactions are reversible, thus the eliminated
water must be removed if a high molecular weight polymer is to
• Based on the assumption that the polymerization kinetics are
independent of molecular size, the condensation reactions may
all be simplified to:
~~~~COOH + HO~~~~
~~~~COO~~~~ + H2O
• When a monocarboxylic acid reacts with an amine,
amide is formed.
• When a carboxylic acid with two –COOH groups
reacts with an amine with two –NH2 groups, a
polyamide is formed.
• When a monocarboxylic acid reacts with an alcohol,
and ester is formed.
• When a carboxylic acid with two –COOH groups
reacts with an alcohol with two –OH groups, a
polyester is formed.
• Addition : monomers with double bonds are joined
together by covalent bonds to form a large molecule
(polymer) without loss of a small molecule.
• Monomers for making addition polymers may be
alkenes (ethene and propene) or alkene derivatives
(choloroethene, CH2 = CHCl)
• In the formation of addition polymers, the carboncarbon double bond in each monomer is broken
open and replaced by a carbon-carbon single bond.
• Chain polymerization proceeds by the succession of
three steps :
– Initiation : The first active center (radical, anion or
cation) is formed and the growth of the chain is
– Propagation : Growth of the polymer chain occurs
by the successive addition of monomers to the
active center at the end of the chain.
– Termination : Growth is terminated by either
neutralization or transfer of the active center.
Vinyl monomers for addition polymerizations
The only exceptions to the unreactivity
of tri- and tetra-substituted vinyl
monomers are those with fluorine, like
tetrafluoroethylene (CF2=CF2). The
main cause of this reactivity pattern is
the steric size of the substituents.
EXAMPLES OF ADDITION
• Polyethylene (PE)
• Polyvinyl Chloride (PVC)
• The IUPAC name for polyvinyl chloride is
poly(chloroethene) while for vinyl chloride
(monomer) is chloroethene.
• Teflon (PTFE)
• The IUPAC name for Teflon is
• Polymeric materials are used in and on soil to improve
aeration, provide mulch, and promote plant growth and
• Many biomaterials, especially heart valve replacements
and blood vessels, are made of polymers like Dacron,
Teflon and polyurethane.
• Plastic containers of all shapes and sizes are light weight
and economically less expensive than the more
traditional containers. Clothing, floor coverings, garbage
disposal bags, and packaging are other polymer
• Automobile parts, windshields for fighter planes,
pipes, tanks, packing materials, insulation, wood
substitutes, adhesives, matrix for composites, and
elastomers are all polymer applications used in the
• Playground equipment, various balls, golf clubs,
swimming pools, and protective helmets are often
produced from polymers.