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D. JAGAN MOHAN
New Technology Research Centre
University of West Bohemia
Plzen, Czech Republic
POLYMER STRUCTURE
mer mer
mer mer
mer
mer
mer mer mer mer
Polymers consist of long chains, which are composed of simple
structural units (mers) strung together.
Polymers
“poly’’ = many
Synthetic polymers
Polymers – Natural and Synthetic
chain-growth (addition)
step-growth (condensation)
Chemistry(polymer composition)
Size(Molecular Weight)
Shape (chain twisting, entanglement etc.) Structure
Linear Branched Cross linked Network
Isomeric states
Stereoisomers Geometrical isomers
Isotactic Syndiotactic Atactic Cis Trans
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
called vulcanization.
Vulcanization results in cross-linking of the
hydrocarbon chains by disulfide bonds.
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.
disulfide bond
disulfide bond
disulfide bond
Natural and Synthetic Rubber
Ex: conversion of vinyl chloride to poly(vinyl chloride)
Prepared by chain reactions.
Monomers are added to the growing end of a polymer chain.
vinyl chloride Poly(vinyl chloride)
Monomer Polymer
Step-growth polymerization is used to prepare polyamides, polyurethanes, polycarbonates and polyesters.
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.
Monomers
Polymer
Nylon 6,6 HCl
Linear
BranchedCross-linked
Network
Molecular Structure
Physical properties of polymers depend not only on their molecular
weight/shape, but also on the difference in the chain structure
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
Polymerizationby 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).
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:
Monomers unit are crosslinked together to form a three dimensional network polymers.
A cross-link is a bond that links one polymer chain to another (Covalent or Ionic bonds).
Polymer chain
Polymer chain
Crosslink
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
….. is a polymer made up of only
one type of monomer
( CF2 CF2 )n
Teflon
( CH2 CH2 )n
Polyethylene
( CH2 CH )n
ClPVC
Homopolymer….
…. is a polymer made up of two or more monomers
Styrene-butadiene rubber
( CH CH2 CH2 CH CH CH2 )n
Copolymer …
Alternating
Block
Random
Graft
A B
A and B alternate in polymer chain
large blocks of A units alternate with
large blocks of B units
A and B randomly positioned along chain
chains of B units grafted onto A backbone
Copolymers
two or more monomers polymerized together
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
Isomerism
compounds with same chemical formula can have quite different structures
C C C C C C C CH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3=
Ex: Octane C8H18
H3C CH2 CH3( )6
H3C CH
CH3
CH2 CH
CH2
CH3
CH3
2,4 Dimethyl hexane
Isomerism – compounds of the same chemical
composition but different atomic arrangements
(i.e. bonding connectivity)
Polymers that have more than one type of side atom or group can have a variety of configurations
Stereoisomerism
Stereoisomers of Polymers
Isotactic
Syndiotactic
Atactic
All of the R groups are on the same side of the chain
C
C
C
C
C
C
C
R R R R
H H H
H H H H
HHH
Isotactic polymers are usually semicrystalline and often form a helix configuration.
R group occupies alternate side of chain
C
C
C
C
C
C
C
R H R H
H H H
H R H R
HHH
R group occupies random side of chain
C
C
C
C
C
C
C
R R H R
H H H
H H R H
HHH
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 atom and CH3 group on same side of chain
H atom and CH3 group on opposite sides of chain
transtrans-isoprene
ciscis-isoprene
Geometrical Isomers
C CCH3
CH2
CH2
H
C CHCH3
CH2 CH2
Cis-1,2-dibromoethane
Trans 2 butene
C C
CH3 H
CH3H
C C
Br Br
H H
A.
B.
C C
CH3 Cl
ClH
C.
C C
H Br
H CH3
C C
H Br
BrH
No Cis-Transidentical
•Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.
O
O O
O
O
CC
C C
O Ar 2N Ar' NH2
O
O O
O
OCC
C C
O
Ar
H
NH Ar'
H
NH ][
O
O O
O
CC
C C
Ar Ar'N ][ N
O
-H20
0~5 C 2hr, 12hr at RTO
DMF
Poly(amic acid)
H
250C, 4hr
Polyimide
Synthesis of Polyimides
Membranes
Aerospace
Telecommunication
Space applications
Photolithography
House hold materials, etc.
Several methods are possible to prepare
polyimides:
Reaction between a dianhydride and a diamine
Reaction between a dianhydride and a diisocyanateApplications
Diamine amic acids
Poly(amide amic acid)s
OO
O O
O
CC
C C
OH2N Ar' NH2Ar
H2N Ar' NH
OH
OH
NH2NH Ar'
OO
O O
CC
C C
O
Ar
DMF
O
[ C
C
O
O
HO
NHAr'HN
ClOC Ar'' COCl
]
C
C
O
O
Ar''NH
HO
C
O
C
O
Ar' NH
0~5 C 2hr, 24 hr at RT
Ar
0~5 C 2 hr, 6 hr at RT
DMF
Synthesis of Polyamide-imides
(Anhydride)
(Diamine)
(Acid chloride)
CNHAr' Ar'
OO
O O
CC
C C][ N N
200 C, 4hro
O
HN Ar'' C
O
Poly(amide imide)s
Poly(amide amic acid)s
[ C
C
O
O
HO
NHAr'HN
]
C
C
O
O
Ar''NH
HO
C
O
C
O
Ar' NH
250C, 4hr –H2O
Solid
Imide group Amide group
Ar
Ar
Poly(amide amic acid) to Polyamide-imides
O O
OHOH
NH2
O
NH2
OH OH
Formation of a polyamide
O O
OHOH
NH
O
NH2
OH+ H2OO
NH2
NH2OH
Formation of a polyamide
O
NH2
NH2 NH
O O
OHOH
NH
O
OH+ H2O
+ H2OO
NH2
OH
Formation of a polyamide
O
NH2
NH
O
NH2 NH
O O
OHOH
NH
O
OH+ H2O
+ H2O
+ H2O
Formation of a polyamide
O
NH2
NH
O
NH2 NH
O O
OHOH
NH
O
OH
A polyamide “backbone” forms with R groups
coming off. This protein is built with amino acids.
Formation of a polyamide
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
CO2H
RH R is the only variable group
+H3N C C O- + +H3N C C O-
H
R1
H
R2
O O
Monomers: 20 essential amino acids
+H3N C C N C C O- + H2O
H
R1
H
R2
O O
H
Peptide bond
Proteins
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].
Polyhydroxyalkanoate R = CH3, 3-hydroxybutyric acid
R = CH2CH3, 3-hydroxyvaleric acid
3-hydroxy carboxylic acidPHA
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
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
Plasticizers
Conclusion
Natural and Synthetic Polymers
Homopolymers
Copolymers- Alternating, block, random and graft
Synthesis of Polyamide, polyimides, poly(amide imides)s.
Biodegradable polymers, Plasticizers, Proteins etc
Stereoisomers of Polymers- Isotactic, syndiotactic and atactic
Geometrical Isomers – cis and trans
Thank You
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