Polymer Properties and Polymer Properties and StructureStructure

The age of the plastic fantasticThe age of the plastic fantastic

Learning objectivesLearning objectives

Describe basic features of a polymerDescribe basic features of a polymer Name three steps in the addition Name three steps in the addition

polymerization processpolymerization process Distinguish between addition and Distinguish between addition and

condensation polymerizationcondensation polymerization Describe essential features of condensation Describe essential features of condensation

polymerization polymerization Identify polymerization process used on basis Identify polymerization process used on basis

of polymer compositionof polymer composition

Polymers are large molecules made by Polymers are large molecules made by concatenation of many small unitsconcatenation of many small units

Building blocks are Building blocks are monomersmonomers A polymer may contain thousands of A polymer may contain thousands of

monomers and have a molar mass of hundreds monomers and have a molar mass of hundreds of thousandsof thousands Homopolymer Homopolymer – the monomers are identical– the monomers are identical CopolymerCopolymer – the monomers are different (2 or – the monomers are different (2 or

more)more)

MonomerMonomer A monomer must be capable of forming A monomer must be capable of forming two two

bonds to generate a chainbonds to generate a chain A double bond meets that requirementA double bond meets that requirement

Two main synthetic Two main synthetic approachesapproaches

Addition Addition polymerizationpolymerizationSimply adding monomers together – Simply adding monomers together –

synthetic plasticssynthetic plastics

Condensation Condensation polymerizationpolymerizationCombination by exclusion of a small Combination by exclusion of a small

molecule (usually water) – molecule (usually water) – extensively used by natureextensively used by nature

Reactive radical to initiate the Reactive radical to initiate the processprocess

Radicals are reactive – contain unpaired electronsRadicals are reactive – contain unpaired electrons

Odd + even = odd: unpaired electron survivesOdd + even = odd: unpaired electron survives

H

HH

H H

HH

H H

HH

H

R●

●

R R

Addition polymerization has three stepsAddition polymerization has three steps

CC22HH44 is stable – does not spontaneously change is stable – does not spontaneously change

into polyethylene – requires severe conditionsinto polyethylene – requires severe conditions

1.1. InitiationInitiation – create reactive species by – create reactive species by formation of free radical (unpaired electron)formation of free radical (unpaired electron)

2.2. PropagationPropagation – As chain grows by addition of – As chain grows by addition of CC22HH44 units, the radical is preserved units, the radical is preserved

3.3. TerminationTermination – radicals eliminated when they – radicals eliminated when they meetmeet

Polymer properties tuned by Polymer properties tuned by modifying added groupsmodifying added groups

DensityDensity PolarityPolarity Chain branchingChain branching Cross linkingCross linking Chain lengthChain length

Structure is functionStructure is function

HDPE: the strands pack closely togetherHDPE: the strands pack closely together LDPE: branches prevent close packingLDPE: branches prevent close packing

Polymers have revolutionized containers Polymers have revolutionized containers and other household itemsand other household items

Common addition polymers cont’dCommon addition polymers cont’d

Condensation polymers: another Condensation polymers: another route to making chainsroute to making chains

Two types of monomer required – each Two types of monomer required – each capable of making two bondscapable of making two bonds

Bonding occurs between them by elimination Bonding occurs between them by elimination of components of waterof components of water OH + H = HOH + H = H22OO

Lower temperature process than addition Lower temperature process than addition polymerizationpolymerization

Condensation polymer productsCondensation polymer products

Building Blocks of ProteinsBuilding Blocks of Proteins

Alanine

Glycine

Leucine

Nature’s building blocks contain –CO-NH-C- groups – amide links. The monomers are amino acids. Glycine is the simplest. There are twenty altogether

-CO2H -NH2

Polypeptide ChainsPolypeptide Chains

Condensation of amino acids creates polypeptide chains. Hemoglobin contains four chains, which imprison an iron atom. The iron atom binds with oxygen (or CO or cyanide ion)

The amide linkThe amide link

Why –CO-NH-C- (amide) rather than –CO-O-C- (ester)?

No facility for H-bonding in –CO-O-C- H atom in –CO-NH-C- provides H-bonding

for secondary structure control

Hair and WoolHair and WoolSecondary and tertiary structures of peptide chains (α-keratin) in the structure of hair. Hydrogen bonding plays a crucial role in this process.

Glucose and CelluloseGlucose and Cellulose

Cellulose is a condensation polymer of the simplest carbohydrate, glucose. Only C,H and O are involved. Cellulose is the most abundant organic chemical on earth.

Polymer design is unlimitedPolymer design is unlimited

ApplicationsApplications NanoelectronicsNanoelectronics SensorsSensors Catalysis Catalysis

Dendrimers