1. POLYMER STRUCTURE D. JAGAN MOHAN New Technology Research Centre
University of West Bohemia
Plzen, Czech Republic

2. Polymers – Natural and Synthetic
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
mer
mer
Polymers – Natural and Synthetic
chain-growth (addition)
Synthetic polymers
step-growth (condensation)

3. Molecular characteristics
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

4. 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 called vulcanization.
disulfide bond
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.

5. 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
Poly(vinyl chloride)
Monomer
Polymer

6. 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

7. Molecular Structure Structures
Physical properties of polymers depend not only on their molecular weight/shape, but also on the difference in the chain structure
Structures
Network
Linear
Cross-linked
Branched

8. Linear Polymers
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

9. Branched Polymers 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).

10. Cross-linked Polymers
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:

11. Network Polymers
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

12. ( CF2 CF2 )n ( CH2 CH2 )n ( CH2 CH )n Cl Homopolymer….
….. is a polymer made up of only one type of monomer
( CF2 CF2 )n
Teflon
( CH2 CH2 )n
Polyethylene
( CH2 CH )n Cl
PVC

13. Copolymer …
…. is a polymer made up of two or more monomers
( CH CH2 CH2 CH CH CH2 )n
Styrene-butadiene rubber

14. two or more monomers polymerized together
Copolymers
two or more monomers polymerized together A B
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
large blocks of A units alternate with large blocks of B units
Block
Random
A and B randomly positioned along chain
Graft
chains of B units grafted onto A backbone

15. Isomerism
compounds with same chemical formula can have quite different structures
Ex: Octane C8H18
2,4 Dimethyl hexane
Isomerism – compounds of the same chemical composition but different atomic arrangements (i.e. bonding connectivity)

16. 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

17. Isotactic All of the R groups are on the same side of the chain
Isotactic polymers are usually semicrystalline and often form a helix configuration.

18. Syndiotactic
R group occupies alternate side of chain

19. Atactic 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

20. Geometrical Isomers cis cis-isoprene trans trans-isoprene
H atom and CH3 group on same side of chain
H atom and CH3 group on opposite sides of chain

21. Cis-1,2-dibromoethane
Trans 2 butene
Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.
identical
No Cis-Trans

22. Synthesis of PolyimidesC Ar 2 N
Ar' NH H ] [ -H
0~5 C 2hr, 12hr at RT
DMF
Poly(amic acid)
250C, 4hr
Polyimide
Several methods are possible to prepare polyimides:
Reaction between a dianhydride and a diamine
Reaction between a dianhydride and a diisocyanate
Applications
Membranes
Aerospace
Telecommunication
Space applications
Photolithography
House hold materials, etc.

23. Synthesis of Polyamide-imides2 N
Ar' NH O C Ar Ar
DMF
0~5 C 2 hr, 6 hr at RT
(Diamine)
(Anhydride)
Diamine amic acids
(Acid chloride) Ar
Poly(amide amic acid)s

24. Poly(amide amic acid) to Polyamide-imides[ C O H NH
Ar' HN ]
Ar'' Ar
Poly(amide amic acid)s
Solid
250C, 4hr
–H2O Ar
Poly(amide imide)s
Amide group
Imide group

25. Formation of a polyamide

26. Formation of a polyamide
+ H2O

27. Formation of a polyamide
+ H2O
+ H2O

28. Formation of a polyamide
+ H2O
+ H2O
+ H2O

29. Formation of a polyamide
A polyamide “backbone” forms with R groups coming off. This protein is built with amino acids.

30. Monomers: 20 essential amino acids
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
R is the only variable group
Monomers: 20 essential amino acids
+H3N C C O- + +H3N C C O- H R1 R2 O
+H3N C C N C C O- + H2O H R1 R2 O
Peptide bond

31. 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
3-hydroxy carboxylic acid
Polyhydroxyalkanoate
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

32. 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

33. 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

34. Thank You