PLASTICS AND POLYMERS
Chapter 12
TEFLON
Describe the following terms:
Macromolecule:
A molecule that consists of a large number of
atoms.
Polymer:
A large molecule composed of smaller
monomer units covalently bonded to each
other in a repeating pattern.
Monomer:
Small organic molecules that can be covalently
bonded to each other in a repeating pattern.
Polymerisation:
A chemical reaction in which monomer
molecules join to form a polymer.
Addition polymerisation: A reaction in which small molecules join to form
very large molecules by adding on double bonds.
Addition polymer:
A polymer formed when monomers combine
through an addition reaction.
Condensation polymerisation: Molecules of two monomers with different
functional groups undergo condensation
reactions with the loss of small molecules,
usually water.
Condensation polymer:
A polymer formed by two monomers with
different functional groups that are linked
together in a condensation reaction in which a
small molecule, usually water, is lost.
Free radical:
A molecular fragment with an unpaired electron.
ADDITION POLYMERISATION
This is done by joining together monomers which have C=C bonds to end up with long-chain
molecules with C–C bonds.
By changing the monomer one gets plastics with different properties.
One can represent a polymer by abbreviating on a monomer level.
For example Teflon (page 1) can be abbreviated as:
It was made by adding together numerous tetrafluoroethene molecules.
Addition polymerization occurs in a three step process as seen in this example of forming
polythene (“polyethene”):
1. Initiation:- a free radical is generated which attacks a double bond of a monomer.
(H2O2 is often used to generate free radicals.)
R• + CH2=CH2  R–CH2–CH2•
2. Propagation:- the new free radical adds to another monomer creating a new longer
free radical and this process continues creating a long chain – a polymer.
R–CH2–CH2• + CH2=CH2  R–CH2–CH2–CH2–CH2•
etc etc
Until a long chain radical is formed……..
R–CH2–CH2– CH2–CH2– CH2–[CH2]n– CH2–CH2– CH2–CH2– CH2–CH2•
3. Termination:- two free radicals can join together to form an alkane:
R–CH2–[CH2]n– CH2• + •CH2–[CH2]n– CH2–R
 R–CH2–[CH2]n– CH2–CH2–[CH2]n– CH2–R
or a free radical can remove an H from another free radical to form
an alkane and an alkene
R–CH2–[CH2]n– CH2• + •CH2–CH2– CH2–R
 R–CH2–[CH2]n– CH3 + CH2=CH– CH2–R
Polythene is the most common plastic and is used to make shopping bags, rulers, many
containers and a myriad of other cheap items.
CONDENSATION POLYMERIZATION
This is done by having monomers which have functional groups which react together and in
the process eliminate a small molecule. The most common example is the reaction between
alcohols and carboxylic acids (both of which have functional groups at each end) to form
esters – polyesters.
H–O–CH2–[CH2]n–CH2–O–H + HOOC–[CH2]n–COOH
O
ǁ
 H–O–CH2– [CH2]n–CH2–O–OC–[CH2]n–COOH
ester linkage
Polyesters are used to make clothes, drinking bottles (PET)…
Another famous example of a condensation polymer is Nylon. It is a polyamide.
Properties of plastics
1. Light
2. Strong – the longer the molecules the stronger they tend to be.
3. Non-biodegradable – so do present a problem for disposal. Recycling has become
more common to avoid this problem.
4. Insulators of heat and electricity.
5. Flexibility – this is determined primarily by the degree of cross-linking between
chairs. The more cross-linking the more rigid the structure.
Thermoplastics:
Thermosets:
Melt on heating and when cool they set in new shapes.
e.g. polythene, nylon, polyvinyl chloride
Break down at high temperatures so cannot be remoulded
e.g. melamine
Plastics and their uses.
Plastic
polythene
nylon
PET
poly vinyl chloride PVC
Teflon
Kevlar
Aramid
poly(methyl methacrylate) PMMA
Mylar
Recycling – page 159
Uses
bags, bottles
rope, stockings
water bottles
pipes, flooring
Non-stick
body armour, tires.
brakes
windscreens
Roasting bags ++