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