Organic Chemistry VIntroduction to Polymer Chemistry

Indra Yudhipratama

Outline

Defining the terms in polymer Type of polymers Polymer synthesis (Polymerisation) and the properties of its

product Addition polymerisation

Polyalkenes Condensation polymerisation

Polyesters Polyamides

Enhancing the polymers

Introduction Polymers in daily life

All of those are synthetic polymers. Mother nature also produces polymers.

Defining Polymer

Polymers Poly (many) + mer (unit) Hence polymer is a macromolecule that is built from

smaller unit (monomer) Proteins are built from many amino acids. Proteins are

polymers, amino acids are the monomers A polymer can be built from the same monomer

Homopolymer e.g. Poly(tetrafluoroethene) Also can be built from different monomers Copolymer

e.g. ABS (Acrylonitrile-Butadiene-Styrene)

Type of Polymers

Poly(tetrafluoroethene) ABS

Polymerisation

Addition polymerisation Involving radicals chemistry Three main steps:

Initiation An initiator is required to start reaction

Propagation The chain is propagated to form a long chain

Termination Reacts with another radical species to stop the reaction

Addition Polymerisation E.g. Synthesis of Poly(chloroethene) or PVC Initiation step

Propagation step

Termination step

ClR ClR

ClClR

R

Cl Cl

R

Cl Cl

x

R

Cl Cl

x

R

ClCl

y

R

Cl Cl

Cl Cl

R

x y

Cl

n

Addition Polymerisation The product of addition polymerisation

From alkene alkane, hence stronger in structure. More rigid/solid structure

The products could have different arrangement: Regular structure provides rigid, tough, heat resistant polymers.

Known as Isotactic

Commonly used for food containers, hospital equipments.

H Cl H Cl H Cl H Cl H Cl H Cl H Cl H Cl

Addition Polymerisation The product could have different arrangement:

Irregular structure provides more flexible and softer polymers. Known as atactic.

Used as sealants and coatings. Third type, the functional group alternates between one side and

others, known as syndiotactic. This also has regular structure.

H Cl H Cl Cl H H ClCl HCl H H Cl H Cl

Cl H H Cl Cl H H ClCl H H Cl Cl H H Cl

Condensation Polymerisation Producing small molecules as side products. Commonly water is the small molecules, hence the process known as

condensation.

Polyester formation Difunctional groups are required to form condensation polymers. Dicarboxylic acids with diols to form polyesters

HO R

O

OH

O

HO R' OHn n+

R

O

O

O

R' O

nwhere R and R' are alkyl or aromatic carbon chains.

PolyestersPolyesters in daily life Poly(ethylene terephtalate) or known as PET. The monomers are phtalic acid and ethane-1,2-diol.

A rigid structure due to benzene rings. Used as plastic bottle

OH

O

HO

O

+ HOOH Sb(III) catalyst

280oC

O O

O

O

n

Polyamides Has amide linkage, occur in nature e.g. proteins. Formed from amino acids

Synthesised in laboratory from diacyl chlorides and diamines Problem in synthesis with dicarboxylic acids and diamines

H2NOH

O

R

nNH

HN

O

R

R

O

n

Cl R

O

Cl

O

H2N R' NH2n n+

R

O

NH

O

R' NH

nwhere R and R' are alkyl or aromatic carbon chains.

Polyamides Polyamides in daily life Nylon

Two types of nylon: Nylon-6 Synthesised from caprolactam

HO

O

NH2NH

O

O

NH

n

caprolactam6-aminohexanoic acid nylon-6

Polyamides Two types of nylon:

Nylon-6,6 Synthesised from hexane-1,6-dioic acid and 1,6-diaminohexane

Long alkyl chain gives the flexibility of nylon. Strong structure of polyamides due to hydrogen bonding and amide

bonds No strong hydrogen bonding in polyesters

HO

O

OH

O

+ H2NNH2

n n

O

NH

OHN

n

Enhancing the Polymers’ Properties Some polymers are synthesised to meet the

market requirements. Properties of polymers determine its

function on the market Example: Hardness, hydrophilicity

Changing the monomers would change the properties of polymers Some methods to change the hardness of

the polymers: Using cross-linker Shortening the monomer chain Using the aromatic functional group

Enhancing the Polymers’ Properties

Forming crosslink Natural rubber (rubber band) vs Tyres

Both of them are poly(isoprene)

Tyres manufacturing using sulphur as cross-linker Vulcanisation process

Bind different polymer chains covalently

n

Enhancing the Polymers Vulcanisation process Sulphur as cross-linker

The covalent bonds of sulphur keeps the shape

Enhancing the Polymers

Forming crosslink Manipulating the monomers Difunctional monomers are used

Case of contact lenses Can be polymerised at both ends Forming polymer networks

hydrogels

O

O

O

O

Enhancing the Polymers Shortening the monomers

Case of pacemaker (polyurethanes) Polyurethanes are copolymer Consists of different monomers

Shorter chain (blue) gives the rigidity while the longer chain (red) gives the flexibility over the pacemaker The flexibility over sp3 carbon chain (free rotation)

Enhancing the Polymers Using aromatic functional group

Case of Nylon vs Kevlar

The planar structure of benzene ring causes the polymer can be packed more closely.

Increase rigidity of the polymer

O

NH

OHN

n

Nylon-6,6

O

NH

O

HN

n

Kevlar

Inorganic Polymers

Non-carbon based polymers can also be synthesised Silicone

Si-based polymers PDMS

Poly(dimethylsiloxane) Hydrophobic liquid

polymer with highly flexible chains

Widely used in shampoo formulation

Known as dimethicone

SiO

n

Inorganic Polymers

Silicone hybrid Used in contact lenses Combined with carbon-based polymers

O

O

OSi

O

On

mn

N O+