Transcript Polymers History of Polymers

Polymers
Polymerisation - Methods of sticking Mers together
The process of sticking mers together is called
polymerisation. The two ways of doing this are;
1- Additional polymerisation, this is the most
important of the two because most important
polymers are made this way and,
2- Condensation polymerisation. This method
tends to yield rigid plastics.
Polymers
Addition Polymerisation
The basic idea of sticking mers together like this
is similar to a zip. The mers are added onto
the end of a growing chain. There are three
basic parts to the process:
Initiation - Polyethylene C2H4, has a double
bond between the carbon atoms. One of
these bonds is stronger, while the other is
weak. Each bond contains two electrons. The
weak bond is attacked by a radical.
Polymers
Addition Polymerisation
This radical grabs an electron and leaves one
electron behind.
Propagation -When other ethylene molecules
come near the ethylene radical they too are
attacked and a mer is attached. The combined
molecule is a growing chain radical. The
process continues by adding other ethylene
molecules in a similar fashion.
Polymers
Addition Polymerisation
Termination - Possible stops to the growing
chains could simply be running out of mers
or radicals.
Polymers
Condensation Polymerisation
This process depends on splicing rather than zipping.
The starting molecules are spliced or joined together
with small molecules, like water, being condensed
out of the reaction at the end of polymerisation.
The remaining structure is a comples 3D structure
which is rigid and has a significant cross-linking
feature.
Polymers
Condensation Polymerisation
H
.
Formaldehyde
OH
C=O
H
Phenol
OH H
OH
C
H
+H2O
Polymers
Types of Polymers
Thermoplastics:
These are thermosoftening polymers and make
up about 85 - 90% of the bulk of polymers.
They include;
High Density Polyethylene --HDPE
Low Density Polyethylene --LDPE
Poly Vinyl Chloride
--PVC
Polystyrene
-- PS
Polypropylene
-- PP
Polymers
Types of Polymers
Thermosetting:
The important ones in this group include;
Phenolics - This is a group of polymers based on
phenol formaldehyde (PF) the original
developed by bakeland. It is a cheap, brittle,
muddy-brown (or black or blue) polymer.
Urea-formaldehyde - A white polymer that can be
easily coloured. Uses include electric plugs,
sockets, and other fittings.
Polymers
Types of Polymers
Melamine-formaldehyde. This is harder, more
scratch resistant and clearer. It can be found in
‘melaware’ and formica table tops
Polyesters - This is the resin used in fibreglass
production.
Epoxies - This polymer is used in adhesives.
Polyurethanes - Are hard to classify as they can
exist as hard glassy polymer or as a soft flexible
sponge.
Polymers
Additives for Polymers
Just as metals are alloyed to improve their
properties, substances are added to polymers to
improve theirs. A typical example is