POLYMERS – MODULE 7
BASICS
(1) Polymer
• Polymers are complex and giant molecules which are made from joining a
large number of small and simple molecules by primary valence linkage.
• These small and simple molecules are called monomers
• The repeating chemical units are covalently linked to each other in a
macromolecule.
• The properties of a polymer are entirely different from those of the
monomers from which it is formed
• The molar masses of polymers vary from 103 to 107.
• Properties of polymers:
➢ As chain length and cross-linking increases, the tensile strength of the
polymer increases.
➢ Polymers do not melt; they change state from crystalline to semi-
crystalline.
➢ Compared to conventional molecules with different side molecules, the
polymer is enabled with hydrogen bonding and ionic bonding resulting in
better cross-linking strength.
➢ Dipole-dipole bonding side chains enable the polymer for high flexibility.
➢ Polymers with Van der Waals forces linking chains are known to be weak,
but give the polymer a low melting point.
(2) Monomer
• Monomer is defined as a simple molecule with two or more binding sites
through which it forms covalent linkages with other monomer molecules to
form the macromolecule.
• Monomers are the building blocks of polymers.
• All simple molecules cannot behave as monomers but only those with two
or more bonding sites can act as monomers.
• Thus, molecules like Ammonia, water, ethanol etc. are not monomers.
,(3) Polymerization
• The process by which the monomer molecules are linked to form a big
molecule is called polymerization.
• Monomer alone cannot undergo polymerization but requires the presence
of a chemical called initiator.
• Eg:
(4) Functionality
• The number of bonding or active sites in a monomer is called its
functionality.
• Eg: The double bonded compounds like ethene, propene is bifunctional.
(5) Degree of Polymerization
• It is defined as the number of monomer molecules forming the polymer
chain.
• Eg: For the polymer shown below, the degree of polymerization is n.
(6) Tacticity
• The physical properties of a polymer depend not only on the type of
monomer(s) that make up the polymer but also on the stereochemical
arrangements of the atoms.
• Tacticity is the relative stereochemistry of adjacent chiral centers within a
macromolecule.
• Three terms to describe Tacticity:
➢ Isotactic polymer
➢ Syndiotactic polymer
➢ Atactic polymer
, • Isotactic polymer: If all chiral centers have the same configuration, the
arrangement of the side groups is called isotactic.
• Syndiotactic polymer: If every other chiral center has the same
arrangement, it is called syndiotactic.
• Atactic polymer: a random arrangement of the side groups is called atactic
or heterotactic.
CLASSIFICATION OF POLYMERS
BASICS
(1) Polymer
• Polymers are complex and giant molecules which are made from joining a
large number of small and simple molecules by primary valence linkage.
• These small and simple molecules are called monomers
• The repeating chemical units are covalently linked to each other in a
macromolecule.
• The properties of a polymer are entirely different from those of the
monomers from which it is formed
• The molar masses of polymers vary from 103 to 107.
• Properties of polymers:
➢ As chain length and cross-linking increases, the tensile strength of the
polymer increases.
➢ Polymers do not melt; they change state from crystalline to semi-
crystalline.
➢ Compared to conventional molecules with different side molecules, the
polymer is enabled with hydrogen bonding and ionic bonding resulting in
better cross-linking strength.
➢ Dipole-dipole bonding side chains enable the polymer for high flexibility.
➢ Polymers with Van der Waals forces linking chains are known to be weak,
but give the polymer a low melting point.
(2) Monomer
• Monomer is defined as a simple molecule with two or more binding sites
through which it forms covalent linkages with other monomer molecules to
form the macromolecule.
• Monomers are the building blocks of polymers.
• All simple molecules cannot behave as monomers but only those with two
or more bonding sites can act as monomers.
• Thus, molecules like Ammonia, water, ethanol etc. are not monomers.
,(3) Polymerization
• The process by which the monomer molecules are linked to form a big
molecule is called polymerization.
• Monomer alone cannot undergo polymerization but requires the presence
of a chemical called initiator.
• Eg:
(4) Functionality
• The number of bonding or active sites in a monomer is called its
functionality.
• Eg: The double bonded compounds like ethene, propene is bifunctional.
(5) Degree of Polymerization
• It is defined as the number of monomer molecules forming the polymer
chain.
• Eg: For the polymer shown below, the degree of polymerization is n.
(6) Tacticity
• The physical properties of a polymer depend not only on the type of
monomer(s) that make up the polymer but also on the stereochemical
arrangements of the atoms.
• Tacticity is the relative stereochemistry of adjacent chiral centers within a
macromolecule.
• Three terms to describe Tacticity:
➢ Isotactic polymer
➢ Syndiotactic polymer
➢ Atactic polymer
, • Isotactic polymer: If all chiral centers have the same configuration, the
arrangement of the side groups is called isotactic.
• Syndiotactic polymer: If every other chiral center has the same
arrangement, it is called syndiotactic.
• Atactic polymer: a random arrangement of the side groups is called atactic
or heterotactic.
CLASSIFICATION OF POLYMERS
