1
UNIT-IV POLYMERS AND HETEROCYCLES 9
Polymers – Introduction - Polymerization - Types of Polymerization - Condensation, Addition,
Coordination, Copolymerization - Mechanism of Polymerization - Free Radical Mechanism -
Biopolymers - PLA and PHB - Synthesis properties and applications.
Heterocyclic compounds - Synthesis and electrophilic and nucleophilic substitution reactions of
pyrrole - furan - thiophene- pyridine- quinoline - isoquinoline.
4.1. INTRODUCTION
Polymers are macromolecules in which a large number of small molecules repeat themselves in a
regular fashion. Thus, small molecules which combine with each other to form polymer molecules are
termed monomers; and the “repeat unit” in a polymer is called as - mer.
For example, polythene is a polymer formed by linking together of a large number of ethene
(C2H4) molecules. Similarly polystyrene is formed by the linking of styrene monomer molecules.
n(CH2 =CH2) [–CH2 – CH2–]n
Ethylene (monomer) Polyethylene (Polymer)
4.1.1 Degree of polymerization
The number of repeating units (n) present in the polymer chain is known as the degree of
polymerisation.
5 CH2 = CH2 ( CH 2 –C H 2 ) 5
Degree of polymerisation = 5
Based on degree of polymerization they are into
i).Oligo polymers - having low degree of polymerization (500-5000)
ii). High polymers - are having higher degree of polymerization (10,000-2.00,000)
4.1.2. Tacticity
It is the orientation of functional groups in a polymer chain is known as Tacticity. The different
orientation of groups (tacticity) can affect the physical properties of polymer.
, 2
There are three kinds of arrangements
1. Isotactic
2. Atactic
3. Syndiotactic
1. Isotactic
It is the configuration or arrangement in which the functional groups are arranged in the same side of
the Isotactic polypropylene For example, in isotactic polypropylene all the methyl groups are on the
same side of the ring.
2. Atactic: It is the configuration or arrangement in which functional groups are arranged randomly.
In Atactic polypropylene the methyl groups are arranged in random manner with respect to carbon
backbone.
3. Syndiotactic
It is the configuration or arrangement in which functional groups are arranged in alternating fashion.
, 3
In syndiotactic polypropylene the methyl groups are arranged in an alternating manner. Generally
polypropylene, Polymethylmethacrylate (PMMA) exists as syndiotactic and isotacticforms.
4.2 Classification of Polymers
Polymers have been classified on different basis as follows:
(A) Classification on the basis of Origin/Source
On this basis, polymers have been broadly classified into two types:
1. Natural Polymers
They occur naturally and are found in plants and animals.
Examples: Proteins, Nucleic acids, Starch, Cellulose and Natural rubber.
2. Synthetic Polymers
These are man-made polymers. Plastic is the most common and widely used synthetic polymer.
e.g., Nylons, Polythene, PVC, Synthetic rubbers, etc.
(B)Classification on the basis of nature of Monomers
On this basis, polymers have been broadly classified into two types:
1. Homo-polymers
Polymers which comprise of only one type of monomers are called as homo-polymers. e.g.,
Polyethene, PVC, Nylon-6 etc. This can be represented as:
-A-A-A-A-A-A-A-A-A-A-A-A-A-A-, or -(A-)n-
2. Co-polymers
Polymers which comprise of more than one (generally two) types of monomers are called as homo-
polymers. e.g., Nylon-6'6, Terylene, SBR,etc. Co-polymers have further been classified into four
types on the basis of relative arrangement of the monomer units with respect to each other. These
are:
i). Alternate Co-polymers: Polymers comprising of alternating A and B units. The order
, 4
is regularly followed throughout the chain. This can be represented as:
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-, or -(A-B)n-
ii). Block Co-polymers: Polymers comprising of regular alternating blocks of A and B
units. The order is regularly followed throughout the chain. This can be represented as:
-A-A-A-A-A-B-B-B-B-B-A-A-A-A-A-B-B-B-B-B-
iii). Graft Co-polymers: Polymers in which the main chain comprises of one type of
monomers and the other monomer forms the branches. Therefore, for being a graft co-
polymer, the polymer must be branched.
This can be represented as:
B B B
-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-B
B B
iv). Random Co-polymers: Polymers in which no regular order of arrangement is followed
by the monomer units. This can be represented as:
-A-A-A-A-A-B-B-A-B-B-B-B-B-B-B-A-A-A-
4.3 Polymerization
The process of formation of a polymer from its monomer units is termed as polymerization.It involves
union of two or more small, same or different monomer molecules to form a single large macro-molecule,
called polymer. The conversion of a monomer into a polymer is an exothermic process and if heat is not
dissipated or properly controlled, explosion may result.
4.3.1 Types of polymerization processes
i) Addition or chain polymerization
ii) Co-polymerization
iii) Condensation or step polymerization.
(i) Addition or chain polymerization:
When monomer units are repeatedly added to form a long chain polymer without the elimination of
any by-product molecule, the product formed is called addition polymer and the process involved is called
addition polymerization.
UNIT-IV POLYMERS AND HETEROCYCLES 9
Polymers – Introduction - Polymerization - Types of Polymerization - Condensation, Addition,
Coordination, Copolymerization - Mechanism of Polymerization - Free Radical Mechanism -
Biopolymers - PLA and PHB - Synthesis properties and applications.
Heterocyclic compounds - Synthesis and electrophilic and nucleophilic substitution reactions of
pyrrole - furan - thiophene- pyridine- quinoline - isoquinoline.
4.1. INTRODUCTION
Polymers are macromolecules in which a large number of small molecules repeat themselves in a
regular fashion. Thus, small molecules which combine with each other to form polymer molecules are
termed monomers; and the “repeat unit” in a polymer is called as - mer.
For example, polythene is a polymer formed by linking together of a large number of ethene
(C2H4) molecules. Similarly polystyrene is formed by the linking of styrene monomer molecules.
n(CH2 =CH2) [–CH2 – CH2–]n
Ethylene (monomer) Polyethylene (Polymer)
4.1.1 Degree of polymerization
The number of repeating units (n) present in the polymer chain is known as the degree of
polymerisation.
5 CH2 = CH2 ( CH 2 –C H 2 ) 5
Degree of polymerisation = 5
Based on degree of polymerization they are into
i).Oligo polymers - having low degree of polymerization (500-5000)
ii). High polymers - are having higher degree of polymerization (10,000-2.00,000)
4.1.2. Tacticity
It is the orientation of functional groups in a polymer chain is known as Tacticity. The different
orientation of groups (tacticity) can affect the physical properties of polymer.
, 2
There are three kinds of arrangements
1. Isotactic
2. Atactic
3. Syndiotactic
1. Isotactic
It is the configuration or arrangement in which the functional groups are arranged in the same side of
the Isotactic polypropylene For example, in isotactic polypropylene all the methyl groups are on the
same side of the ring.
2. Atactic: It is the configuration or arrangement in which functional groups are arranged randomly.
In Atactic polypropylene the methyl groups are arranged in random manner with respect to carbon
backbone.
3. Syndiotactic
It is the configuration or arrangement in which functional groups are arranged in alternating fashion.
, 3
In syndiotactic polypropylene the methyl groups are arranged in an alternating manner. Generally
polypropylene, Polymethylmethacrylate (PMMA) exists as syndiotactic and isotacticforms.
4.2 Classification of Polymers
Polymers have been classified on different basis as follows:
(A) Classification on the basis of Origin/Source
On this basis, polymers have been broadly classified into two types:
1. Natural Polymers
They occur naturally and are found in plants and animals.
Examples: Proteins, Nucleic acids, Starch, Cellulose and Natural rubber.
2. Synthetic Polymers
These are man-made polymers. Plastic is the most common and widely used synthetic polymer.
e.g., Nylons, Polythene, PVC, Synthetic rubbers, etc.
(B)Classification on the basis of nature of Monomers
On this basis, polymers have been broadly classified into two types:
1. Homo-polymers
Polymers which comprise of only one type of monomers are called as homo-polymers. e.g.,
Polyethene, PVC, Nylon-6 etc. This can be represented as:
-A-A-A-A-A-A-A-A-A-A-A-A-A-A-, or -(A-)n-
2. Co-polymers
Polymers which comprise of more than one (generally two) types of monomers are called as homo-
polymers. e.g., Nylon-6'6, Terylene, SBR,etc. Co-polymers have further been classified into four
types on the basis of relative arrangement of the monomer units with respect to each other. These
are:
i). Alternate Co-polymers: Polymers comprising of alternating A and B units. The order
, 4
is regularly followed throughout the chain. This can be represented as:
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-, or -(A-B)n-
ii). Block Co-polymers: Polymers comprising of regular alternating blocks of A and B
units. The order is regularly followed throughout the chain. This can be represented as:
-A-A-A-A-A-B-B-B-B-B-A-A-A-A-A-B-B-B-B-B-
iii). Graft Co-polymers: Polymers in which the main chain comprises of one type of
monomers and the other monomer forms the branches. Therefore, for being a graft co-
polymer, the polymer must be branched.
This can be represented as:
B B B
-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-B
B B
iv). Random Co-polymers: Polymers in which no regular order of arrangement is followed
by the monomer units. This can be represented as:
-A-A-A-A-A-B-B-A-B-B-B-B-B-B-B-A-A-A-
4.3 Polymerization
The process of formation of a polymer from its monomer units is termed as polymerization.It involves
union of two or more small, same or different monomer molecules to form a single large macro-molecule,
called polymer. The conversion of a monomer into a polymer is an exothermic process and if heat is not
dissipated or properly controlled, explosion may result.
4.3.1 Types of polymerization processes
i) Addition or chain polymerization
ii) Co-polymerization
iii) Condensation or step polymerization.
(i) Addition or chain polymerization:
When monomer units are repeatedly added to form a long chain polymer without the elimination of
any by-product molecule, the product formed is called addition polymer and the process involved is called
addition polymerization.
