3. What is a polymer?
• A long molecule made
up from lots of small
molecules called
• monomers.
4. All the same monomer
• Monomers all same
type (A)
• A + A + A + A 🡪
• -A-A-A-A-
• eg poly(ethene)
polychloroethene
PVC
5. Different monomers
• Monomers of two
different types A + B
• A + B + A + B
• 🡪 -A-B-A-B-
• eg polyamides
• polyesters
6. Copolymers
• Copolymers are like polymer alloys.
Different mers are joined to form a mixture
in the backbone, eg. ABS.
• they can be tailored to obtain specific
properties.
9. What Makes Polymers Unique?
• Really big molecules (macromolecules) like
polymers have very different properties than
small molecules. When polymer is melted,
the chains can flow past each other.
Chain entanglement: Long polymer chains
get entangled with each other.
10. Molecular Weight of Polymers
• Unlike small molecules, polymers
• are typically a mixture of differently
• size molecules.
• Only an average molecular
weight can be defined.
11. Longer chains make stronger
polymers.
• There is a critical length
needed before strength
increases.
• An average No. of 100
repeating units is
necessary for HC
polymers but only 40 for
nylons.
12. Crystalline polymers
• Crystallinty is areas in
polymer where chains
packed in a regular way.
• Both amorphous and
crystalline areas can exist
in the same polymer.
• More crystalline polymer
causes stronger and less
flexible polymer.
13. Melting temperature (Tm)
• The (Tm) when applied to polymers
suggests not a solid-liquid phase transition,
but a transition from a crystalline phase to a
solid amorphous phase. Crystalline melting
is only discussed with thermoplastics, as
thermosets will decompose at high
temperatures rather than melt.
14. Glass transition temperature (Tg)
The glass transition temperature (Tg)
describes the temperature at which
amorphous polymers undergo a second
order phase transition from a rubbery,
viscous amorphous solid (fresh spaghetti) to
a brittle, glassy amorphous solid (3 days old
Spaghetti)
15. Tensile strength
• The tensile strength of a material quantifies how much
stress the material will endure before failing. In general
tensile strength increases with polymer chain length.
16. Plasticizers
Are small molecules which occupy position
between polymer chains (like adding water
to mud to make it easy in molding)
1.To increase flexibility, elongation and to
reduce hardness and stiffness.
2.To lower the processing temperature
(energy saving, decomposition preventing)
17. Plasticizers
Plasticizer properties:
• Low viscosity
• High stable towards water and oils.
• Low vapor pressure (Bpt is high).
• Stable towards light and heat.
• Low toxic.
• Compatible.
• Colorless.
18. Stabilizers
• Heat stabilizers (Pd soap, dibasic
phosphate).
• Antioxidants (easy to oxidize-phenols).
• UV absorbants.
• Light stabilizers: carbon black 2% = (1 to
20 years).
19. Fillers
Improves the attitude and lowers the cost (fiber , powder).
• Max. improvement for physical properties.
• Low water absorbance.
• Low specific gravity.
• High polymer wetting.
• Free from abrasives.
• Cheap and available.
• Odorless.
• Color compatible.
20. Polymer additives
• Blowing agents: physical, chemical.
• Antistatic agents: ethoxilated ammins.
• Lubricants: to allow easier processing and to
slides through dies easier {stearates}.
• Colorants: dyes or pigments.
• Reinforcing agents: (glass fiber, kevler).
• Flame retardants: (Cl/F and Br).
• Odorants
