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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+