POLYMER STRUCTURE
D. JAGAN MOHAN
New Technology Research Centre
University of West Bohemia
Plzen, Czech Republic
Polymers
Polymers consist of long chains, which are composed of simple
structural units (mers) strung together.
“poly’’ = many
mer
mer
mer
mer
mer
mer
mer
mer
Polymers – Natural and Synthetic
chain-growth (addition)
Synthetic polymers
step-growth (condensation)
mer
mer
Size
Chemistry
(polymer composition)
Shape
(Molecular Weight)
Linear
(chain twisting, entanglement etc.)
Branched
Cross linked
Isomeric states
Stereoisomers
Isotactic
Syndiotactic
Geometrical isomers
Atactic
Cis
Structure
Trans
Network
Natural and Synthetic Rubber
Natural rubber is too soft to be used in most applications.
When natural rubber is stretched, the chains become elongated and slide past each other
until the material pulls apart.
In 1939, Charles Goodyear discovered that
mixing hot rubber with sulfur produced a
stronger more elastic material. This process is
disulfide bond
called vulcanization.
Vulcanization results in cross-linking of the
hydrocarbon chains by disulfide bonds.
disulfide bond
disulfide bond
When the polymer is stretched, the chains
no longer can slide past each other, and
tearing does not occur.
Vulcanized rubber is an elastomer, a polymer that stretches when stressed but then returns to its
original shape when the stress is alleviated.
Chain-growth polymers (Addition)
Prepared by chain reactions.
Monomers are added to the growing end of a polymer chain.
Ex: conversion of vinyl chloride to poly(vinyl chloride)


vinyl chloride
Monomer
Poly(vinyl chloride)
Polymer
Step-growth polymers (Condensation)
Step-growth polymers are formed when monomers containing two functional
groups come together and lose a small molecule such as H2O or HCl.
In this method, any two reactive molecules can combine, so that monomer is not
necessarily added to the end of a growing chain.
Step-growth polymerization is used to prepare polyamides, polyurethanes,
polycarbonates and polyesters.

Monomers
Polymer
Nylon 6,6

HCl
Molecular Structure
Physical properties of polymers depend not only on their molecular
weight/shape, but also on the difference in the chain structure
Network
Linear
Branched
Cross-linked
These are polymers in which monomeric units are linked together to form linear chain.
These linear polymers are well packed and have high magnitude of intermolecular
forces of attraction and therefore have high densities, high tensile (pulling) strength and
high melting points.
Some common example of linear polymers are high density polyethylene nylon,
polyester, PVC, PAN etc.
Ethylene mer units
Polymerization
by opening of
Double bonds
Polyethylene Chain
Polymer chains can branch :
Monomers are joined to form long chains with side chains or branches of different lengths.
Irregularly packed and therefore, they have low tensile strength, low density, boiling point and
melting points than linear polymers.
These branches are usually a result of side-reactions during the polymerization of the main chain
Some common examples are low density polythene, glycogen, starch etc. (Amylopectin).
Polymer chain
Crosslink
Polymer chain
A cross-link is a bond that links one polymer chain to another (Covalent or Ionic bonds).
Monomers unit are crosslinked together to form a three dimensional network polymers.
Materials often behave very differently from linear polymers
Many “rubbery” polymers are crosslinked to modify their mechanical properties; in that case
it is often called vulcanization
Generally, amorphous polymers are weak and cross-linking adds strength: vulcanized rubber is
polyisoprene with sulphur cross-links:
Polymers that are “trifunctional” instead of bifunctional
There are three points on the mer that can react
This leads to three-dimensional connectivity of the polymer backbone
Highly crosslinked polymers can also be classified as network polymers
Examples: epoxies, phenol-formaldehyde polymers
Homopolymer….
….. is a polymer made up of only one type of
monomer
( CF2
Teflon
CF2 )n
( CH2
CH2 )n
( CH2
Polyethylene
PVC
CH )n
Cl
Copolymer …
…. is a polymer made up of two or more monomers
( CH
CH2
CH2
CH
Styrene-butadiene rubber
CH
CH2 )n
Copolymers
two or more monomers polymerized together
A
Why? If monomer A has interesting properties, and monomer B has (different) interesting
properties, making a “mixture” of monomers should lead to a superior polymer
Alternating
A and B alternate in polymer chain
Block
large blocks of A units alternate with
large blocks of B units
Random
A and B randomly positioned along
chain
Graft
chains of B units grafted onto A backbone
B
Isomerism
compounds with same chemical formula can have quite different structures
Ex: Octane C8H18
H H H H H H H H
H C C C C C C C C H
= H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3
H H H H H H H H
H3C ( CH2 ) CH3
2,4 Dimethyl hexane
6
CH3
H3C CH CH2 CH CH3
Isomerism – compounds of the same chemical
CH2
composition but different atomic arrangements
CH3
(i.e. bonding connectivity)
Stereoisomers of Polymers
Polymers that have more than one type of side atom or group can have a variety of
configurations
Stereoisomerism
Atactic
Isotactic
Syndiotactic
All of the R groups are on the same side of the chain
Isotactic polymers are usually semicrystalline and
often form a helix configuration.
H
R
H
H
C
C
C
C
H
H
H
R
C
C
C
H
R
H
R
H
H
R group occupies alternate side of chain
H
R
H
H
C
C
C
C
H
H
R
H
C
C
C
H
R
R
H
H
H
 R group occupies random side of chain
 Polymers that are formed by free-radical
mechanisms such as polyvinylchloride are
usually atactic. Due to their random nature
atactic polymers are usually amorphous
H
R
H
H
C
C
C
C
H
H
H
R
C
C
C
R
H
H
R
H
H
Geometrical Isomers
CH3
H
C C
CH2
CH2
cis
cis-isoprene
H atom and CH3 group on
same side of chain
CH3
CH2
C C
CH2
H
trans
trans-isoprene
H atom and CH3 group on
opposite sides of chain
Br
Br
Cis-1,2-dibromoethane
C C
A.
H
H
H
CH3
C C
B.
Trans 2 butene
H
CH3
Cl
CH3
C.
identical
HC
H
C
Br
Cl
C C
H
Br
H
C C
No Cis-Trans
CH3
H
Br
•Alkenes cannot have
cis-trans isomers if a
carbon atom in the
double
bond
is
attached to identical
groups.
Synthesis of Polyimides
O
O
C
C
Ar
O
Several methods are possible to prepare polyimides:
H2N Ar' NH2
O
C
C
O
O
O
0~5 C 2hr, 12hr at RT
Reaction between a dianhydride and a diamine
DMF
Reaction between a dianhydride and a diisocyanate
Applications

[ HN
O
O
C
C NH Ar'
Ar
HO C
Membranes
C OH
O
O
 Aerospace
Poly(amic acid)
 Telecommunication

Space applications

Photolithography

House hold materials, etc.
O
250C, 4hr
-H20
[N
O
O
C
C
N Ar'
Ar
C
C
O
O
Polyimide
]
]
Synthesis of Polyamide-imides
O
O
O
C
C
Ar
O
C
O
O
DMF
O
H2N
O
H2N Ar' NH C
Ar' NH2
C OH
Ar
0~5 C 2 hr, 6 hr at RT
C
O
HO C
(Diamine)
C NH Ar' NH2
O
(Anhydride)
O
Diamine amic acids
O
0~5 C 2hr, 24 hr at RT
ClOC Ar'' COCl
DMF
(Acid chloride)
O
O
[HN
Ar' NH C
C OH
Ar
HO C
O
C NH Ar' NH C Ar'' C
O
O
Poly(amide amic acid)s
O
]
Poly(amide amic acid) to Polyamide-imides
O
O
[HN
Ar' NH C
C OH
Ar
C NH Ar' NH C Ar'' C
HO C
O
O
O
]
O
Poly(amide amic acid)s
Solid
250oC, 4hr
2002O
C, 4hr
–H
[ HN Ar'
O
O
C
C
Ar
N
N Ar' NH C Ar'' C
C
C
O
O
Imide group
O
]
O
Amide group
Poly(amide imide)s
Formation of a polyamide
O
HO
O
O
OH
NH2
OH
HO
NH2
Formation of a polyamide
O
HO
O
O
NH + H2O
HO O
H2N
NH2
OH
NH2
OH
Formation of a polyamide
O
O
O
HO
NH + H2O
HO O
H2N
NH
O
NH2
OH
NH2
OH
+ H2O
Formation of a polyamide
O
O
O
HO
NH + H2O
HO O
H2N
NH
O
NH
NH2
OH
+ H2O
+ H2 O
Formation of a polyamide
O
A polyamide “backbone” forms with R groups
O
O
HO
coming off. This protein is built with amino acids.
NH
HO O
H2N
NH
O
NH
NH2
OH
Proteins
Amino acids are the basic structural units of proteins. An amino acid is a compound that
contains at least one amino group (-NH2) and at least one carboxyl group (-COOH)
General structure of an amino acid
NH2
H
R is the only variable group
R
Monomers: 20 essential amino acids
CO2H
H O
H O
+H N
3
C C O- + +H3N C C OR2
R1
Peptide bond
H O
+H N
3
H O
C C N C C O- + H2O
R1
H R2
Biodegradable polymers
A biodegradable polymer is a polymer that can be degraded by microorganisms—bacteria,
fungi, or algae—naturally present in the environment.
Several biodegradable polyesters have now been developed [e.g., polyhydroxyalkanoates
(PHAs), which are polymers of 3-hydroxybutyric acid or 3-hydroxyvaleric acid].
PHA
Polyhydroxyalkanoate
3-hydroxy carboxylic acid
R = CH3, 3-hydroxybutyric acid
R = CH2CH3, 3-hydroxyvaleric acid
PHAs can be used as films, fibers, and coatings for hot beverage cups made of paper.
Bacteria in the soil readily degrade PHAs, and in the presence of oxygen, the final degradation
products are CO2 and H2O
Plasticizers
If a polymer is too stiff and brittle to be used in practical applications, low molecular
weight compounds called plasticizers can be added to soften the polymer and give it
flexibility.
The plasticizer interacts with the polymer chains, replacing some of the intermolecular
interactions between the polymer chains.
Since plasticizers are more volatile than the high molecular weight polymers, they
slowly evaporate making the polymer brittle and easily cracked.
Plasticizers like dibutyl phthalate that contain hydrolysable functional groups are also
slowly degraded by chemical reactions.
dibutyl phthalate
Conclusion
Natural and Synthetic Polymers
Homopolymers
Copolymers- Alternating, block, random and graft
Stereoisomers of Polymers- Isotactic, syndiotactic and atactic
Geometrical Isomers – cis and trans
Synthesis of Polyamide, polyimides, poly(amide imides)s.
Biodegradable polymers, Plasticizers, Proteins etc
Thank You