2. 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
3. Introduction
Polymers in daily life
All of those are synthetic polymers.
Mother nature also produces polymers.
4. 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)
6. 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
7. Addition Polymerisation
E.g. Synthesis of Poly(chloroethene) or PVC
Initiation step
Propagation step
Termination step
8.
9. 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.
10. 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.
11. 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
12. Polyesters
Polyesters 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
13. 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
14. Polyamides
Polyamides in daily life
Nylon
Two types of nylon:
Nylon-6
Synthesised from caprolactam
15. 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
16. 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
17. 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
18. Enhancing the Polymers
Vulcanisation process
Sulphur as cross-linker
The covalent bonds of sulphur keeps the shape
19. 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
20. 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)
21. 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
22. 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